Publications

A catalogue of the deMello Group publications

2018

Stavrakis, S.; Holzner, G.; Choo, J.; deMello, A. High-throughput microfluidic imaging flow cytometry. Current Opinion in Biotechnology 2019, 55, 36–43

Recently, microfluidic-based flow cytometry platforms have been shown to be powerful tools for the manipulation and analysis of single cells and micron-sized particles in flow. That said, current microfluidic flow cytometers are limited in both their analytical throughput and spatial resolution, due to their reliance on single point interrogation schemes. Conversely, high-speed imaging techniques can be applied to a wide variety of problems in which analyte molecules are manipulated at high linear velocities. Such an approach allows a detailed visualization of dynamic events through acquisition of a series of image frames captured with high temporal and spatial resolution. Herein, we describe some of the most significant recent advances in the development of multi-parametric, optofluidic imaging flow cytometry for the enumeration of complex cellular populations.

Yang, T.; Choo, J.; Stavrakis, S.; De Mello. Fluoropolymer Coated PDMS Microfluidic Devices for Application in Organic Synthesis. Chemistry - A European Journal 2018

In recent years there has been huge interest in the development of microfluidic reactors for the synthesis of small molecules and nanomaterials. Such reaction platforms represent a powerful and versatile alternative to traditional formats since they allow for the precise, controlled and flexible management of reactive processes. To date, the majority of microfluidic reactors used in small molecule synthesis have been manufactured using conventional lithographic techniques, from materials such as glasses, ceramics, stainless steel and silicon. Surprisingly, the fabrication of microfluidic devices from such rigid materials remains ill‐defined, complex, and expensive. Accordingly, the microfluidic toolkit for chemical synthesis would significantly benefit from the development of solvent‐resistant microfluidic devices that can be manufactured using soft‐lithographic prototyping methods. Whilst significant advances in the development of solvent‐resistant polymers have been made, only modest steps have been taken towards simplifying their use as microfluidic reactors. Herein, we emphasize the benefits of using a commercially available, amorphous perfluorinated polymer, CYTOP, as a coating with which to transform PDMS into a chemically inert material for use in organic synthesis applications. Its efficacy is demonstrated through the subsequent performance of photooxidation reactions and reactions under extremely acidic or basic conditions.

Wang, X.; Liu, J.; Wang, P.; deMello, A.; Feng, L.; Zhu, X.; Wen, W.; Kodzius, R.; Gong, X. Synthesis of Biomaterials Utilizing Microfluidic Technology. Genes 2018, 9, 283

Recently, microfluidic technologies have attracted an enormous amount of interest as potential new tools for a large range of applications including materials synthesis, chemical and biological detection, drug delivery and screening, point-of-care diagnostics, and in-the-field analysis. Their ability to handle extremely small volumes of fluids is accompanied by additional benefits, most notably, rapid and efficient mass and heat transfer. In addition, reactions performed within microfluidic systems are highly controlled, meaning that many advanced materials, with uniform and bespoke properties, can be synthesized in a direct and rapid manner. In this review, we discuss the utility of microfluidic systems in the synthesis of materials for a variety of biological applications. Such materials include microparticles or microcapsules for drug delivery, nanoscale materials for medicine or cellular assays, and micro- or nanofibers for tissue engineering.

Lignos, I.; Morad, V.; Shynkarenko, Y.; Bernasconi, C.; Maceiczyk, R. M.; Protesescu, L.; Bertolotti, F.; Kumar, S.; Ochsenbein, S. T.; Masciocchi, N.; Guagliardi, A.; Shih, C.-J.; Bodnarchuk, M. I.; deMello, A. J.; Kovalenko, M. Exploration of Near-Infrared-Emissive Colloidal Multinary Lead Halide Perovskite Nanocrystals Using an Automated Microfluidic Platform. ACS Nano 2018, 12, 5504–5517

Hybrid organic–inorganic and fully inorganic lead halide perovskite nanocrystals (NCs) have recently emerged as versatile solution-processable light-emitting and light-harvesting optoelectronic materials. A particularly difficult challenge lies in warranting the practical utility of such semiconductor NCs in the red and infrared spectral regions. In this context, all three archetypal A-site monocationic perovskites—CH3NH3PbI3, CH(NH2)2PbI3, and CsPbI3—suffer from either chemical or thermodynamic instabilities in their bulk form. A promising approach toward the mitigation of these challenges lies in the formation of multinary compositions (mixed cation and mixed anion). In the case of multinary colloidal NCs, such as quinary CsxFA1–xPb(Br1–yIy)3 NCs, the outcome of the synthesis is defined by a complex interplay between the bulk thermodynamics of the solid solutions, crystal surface energies, energetics, dynamics of capping ligands, and the multiple effects of the reagents in solution. Accordingly, the rational synthesis of such NCs is a formidable challenge. Herein, we show that droplet-based microfluidics can successfully tackle this problem and synthesize CsxFA1–xPbI3 and CsxFA1–xPb(Br1–yIy)3 NCs in both a time- and cost-efficient manner. Rapid in situ photoluminescence and absorption measurements allow for thorough parametric screening, thereby permitting precise optical engineering of these NCs. In this showcase study, we fine-tune the photoluminescence maxima of such multinary NCs between 700 and 800 nm, minimize their emission line widths (to below 40 nm), and maximize their photoluminescence quantum efficiencies (up to 89%) and phase/chemical stabilities. Detailed structural analysis revealed that the CsxFA1–xPb(Br1–yIy)3 NCs adopt a cubic perovskite structure of FAPbI3, with iodide anions partially substituted by bromide ions. Most importantly, we demonstrate the excellent transference of reaction parameters from microfluidics to a conventional flask-based environment, thereby enabling up-scaling and further implementation in optoelectronic devices. As an example, CsxFA1–xPb(Br1–yIy)3 NCs with an emission maximum at 735 nm were integrated into light-emitting diodes, exhibiting a high external quantum efficiency of 5.9% and a very narrow electroluminescence spectral bandwidth of 27 nm.

Bezinge, L.; Maceiczyk, R. M.; Lignos, I.; Kovalenko, M. V.; deMello, A. J. Pick a Color MARIA: Adaptive Sampling Enables the Rapid Identification of Complex Perovskite Nanocrystal Compositions with Defined Emission Characteristics. ACS Applied Materials & Interfaces 2018, 10, 18869–18878

Recent advances in the development of hybrid organic–inorganic lead halide perovskite (LHP) nanocrystals (NCs) have demonstrated their versatility and potential application in photovoltaics and as light sources through compositional tuning of optical properties. That said, due to their compositional complexity, the targeted synthesis of mixed-cation and/or mixed-halide LHP NCs still represents an immense challenge for traditional batch-scale chemistry. To address this limitation, we herein report the integration of a high-throughput segmented-flow microfluidic reactor and a self-optimizing algorithm for the synthesis of NCs with defined emission properties. The algorithm, named Multiparametric Automated Regression Kriging Interpolation and Adaptive Sampling (MARIA), iteratively computes optimal sampling points at each stage of an experimental sequence to reach a target emission peak wavelength based on spectroscopic measurements. We demonstrate the efficacy of the method through the synthesis of multinary LHP NCs, (Cs/FA)Pb(I/Br)3 (FA = formamidinium) and (Rb/Cs/FA)Pb(I/Br)3 NCs, using MARIA to rapidly identify reagent concentrations that yield user-defined photoluminescence peak wavelengths in the green–red spectral region. The procedure returns a robust model around a target output in far fewer measurements than systematic screening of parametric space and additionally enables the prediction of other spectral properties, such as, full-width at half-maximum and intensity, for conditions yielding NCs with similar emission peak wavelength.

Berger, S.; Lattmann, E.; Aegerter-Wilmsen, T.; Hengartner, M.; Hajnal, A.; deMello, A.; Casadevall i Solvas, X. Long-term C. elegans immobilization enables high resolution developmental studies in vivo. Lab on a Chip 2018, 18, 1359–1368

Live-imaging of C. elegans is essential for the study of conserved cellular pathways (e.g. EGFR/Wnt signaling) and morphogenesis in vivo. However, the usefulness of live imaging as a research tool has been severely limited by the need to immobilize worms prior to and during imaging. Conventionally, immobilization is achieved by employing both physical and chemical interventions. These are known to significantly affect many physiological processes, and thus limit our understanding of dynamic developmental processes. Herein we present a novel, easy-to-use microfluidic platform for the long-term immobilization of viable, normally developing C. elegans, compatible with image acquisition at high resolution, thereby overcoming the limitations associated with conventional worm immobilization. The capabilities of the platform are demonstrated through the continuous assessment of anchor cell (AC) invasion and distal tip cell (DTC) migration in larval C. elegans and germ cell apoptosis in adult C. elegans in vivo for the first time.

Sevim, S.; Sorrenti, A.; Franco, C.; Furukawa, S.; Pané, S.; deMello, A. J. Self-assembled materials and supramolecular chemistry within microfluidic environments: From common thermodynamic states to non-equilibrium structures. Chemical Society Reviews 2018, 47, 3788–3803

Self-assembly processes are crucial in the bottom-up fabrication of hierarchical supramolecular structures and advanced functional materials. Their control has traditionally relied on encoded building blocks bearing suitable moieties for recognition and interaction, while targeting the thermodynamic equilibrium state. On the other hand, nature founds the creation of hierarchical organized materials with surprisingly complex biological functions on the ultimate control of reaction diffusion processes. Indeed, under non-equilibrium conditions (kinetic control), the spatio-temporal command of chemical gradients and reactant mixing during self-assembly (e.g. creation of non-uniform chemical environments) can strongly affect the outcome of self-assembly process (i.e. the materials prepared), thus enabling an ultimate control over materials properties and functions. In this tutorial review, we will show how the unique microscale physical conditions offered by microfluidic technologies, in the first place mixing only based on reagent diffusion, can advantageously be used to control the self-assembly of materials, and of supramolecular aggregates in solution, making possible the isolation of intermediate states, unprecedented non-equilibrium structures, as well as the emergence of novel functions. In particular, the selected examples will confirm that microfluidic devices are a valuable toolbox technology to unveil, understand and steer self-assembly pathways to a desired structure and/or property/function, as well as advanced processing tools for device fabrication and integration.

Müller, D.; Nogueira, M.; Cattaneo, S.; Meier, F.; Drexel, R.; Contado, C.; Pagnoni, A.; de Vries, T.; Cohen, D.; Portugal-Cohen, M.; deMello, A. Integration of inverse Supercritical Fluid Extraction and miniaturized Asymmetrical Flow Field-Flow Fractionation for the rapid analysis of nanoparticles in sunscreens. Analytical Chemistry 2018, 90, 3189–3195

We report the use of inverse Supercritical Fluid Extraction (inverse SFE) and miniaturized Asymmetrical Flow Field-Flow Fractionation (mAF4) for the preparation and subsequent analysis of titanium dioxide nanoparticles in model and commercial sunscreens. The approach allows for the fast and reliable fractionation and sizing of TiO2-nanoparticles and their quantitation in commercial products. This new method represents a powerful and efficient tool for the verification of nanoparticle-content in a wide range of matrices, as demanded by recently introduced regu-latory requirements. Furthermore, the use of carbon dioxide as an environmentally friendly solvent is in line with the increasing need for ecologically compatible analytical techniques.

Huber, D.; Oskooei, A.; Casadevall i Solvas, X.; deMello, A.; Kaigala, G. V. Hydrodynamics in cell studies. Chemical Reviews 2018, 118, 2042–2079

Hydrodynamic forces are ubiquitous in living organisms and can be used to manipulate cells or recapitulate physiological microenvironments experienced in vivo. Hydrodynamic effects influence multiple cellular properties and processes, including cell morphology, intracellular processes, cell-cell signalling cascades and reaction kinetics, and play an important role at both the single cell and organ levels. Selected hydrodynamic effects can also be leveraged to control mechanical stresses, analyte transport as well as local temperature within cellular microenvironments. With a better understanding of fluid mechanics at the micron scale and the advent of microfluidic technologies, a new generation of experimental tools that provide for control over cellular microenvironments and recapitulate physiological conditions with exquisite accuracy are now emerging. Accordingly, we believe that it is timely to assess the concepts underlying the hydrodynamic control of cellular microenvironments and their applications, and provide some perspective on the future of such tools in in vitro cell-culture models. Generally, we elucidate the interplay between living cells, hydrodynamic stressors, and fluid-flow-induced effects imposed on the cells. This interplay results in a broad range of chemical, biological and physical phenomena in and around cells. More specifically, we describe and formulate the underlying physics of hydrodynamic phenomena that affect both adherent and non-adherent cells. Moreover, we provide an overview of representative studies that leverage hydrodynamic effects in the context of cell studies within microfluidic systems.\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\r\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n

Lignos, I.; Protesescu, L.; Emiroglu, D. B.; Maceiczyk, R.; Schneider, S.; Kovalenko, M. V.; deMello, A. J. Unveiling the Shape Evolution and Halide-Ion-Segregation in Blue-Emitting Formamidinium Lead Halide Perovskite Nanocrystals Using an Automated Microfluidic Platform. Nano Letters 2018, 18, 1246–1252

Hybrid organic-inorganic perovskites and in particular formamidinium lead halide (FAPbX3, X = Cl, Br, I) perovskite nanocrystals (NCs) have shown great promise for their implementation in optoelectronic devices. Specifically, the Br and I counterparts have shown unprecedented photoluminescence properties, including precise wavelength tuning (530-790 nm), narrow emission linewidths ( less than 100 meV) and high photoluminescence quantum yields (70-90%). However, the controlled formation of blue emitting FAPb(Cl1-xBrx)3 NCs lags behind their green and red counterparts and the mechanism of their formation remains unclear. Herein, we report the formation of FAPb(Cl1-xBrx)3 NCs with stable emission between 440-520 nm in a fully automated droplet-based microfluidic reactor and subsequent reaction upscaling in conventional laboratory glassware. The thorough parametric screening allows for the elucidation of parametric zones (FA-to-Pb and Br-to-Cl molar ratios, temperature and excess oleic acid) for the formation of nanoplatelets and/or NCs. In contrast to CsPb(Cl1-xBrx)3 NCs, based on on-line parametric screening and offline structural characterization, we demonstrate that the controlled synthesis of Cl-rich perovskites (above 60 at% Cl) with stable emission remains a challenge due to fast segregation of halide ions.

Pérez del Pino, A.; González-Campo, A.; Giraldo, S.; Peral, J.; György, E.; Logofatu, C.; deMello, A. J.; Puigmartí-Luis, J. Synthesis of graphene-based photocatalysts for water splitting by laser-induced doping with ionic liquids. Carbon 2018, 130, 48–58

The synthesis of metal-free graphene-based photocatalysts has received great attention recently due to their expected contributions to the development of solar-based hydrogen generation via water-splitting in a low cost and ecological manner. In this work, a new method for the generation of nitrogen-doped graphene-based powder employing an alternative solution to commonly used toxic and hazardous organic solvents is presented. The procedure involves ultraviolet pulsed laser irradiation of graphene oxide (GO) flakes dispersed in 1-butyl-3-methylimidazolium [bmim]-based ionic liquids using both chloride and acetate anions. The structural and compositional analysis using transmission electron mi- croscopy, X-ray photoelectron and infrared spectroscopy indicate that the irradiated GO becomes partially reduced and doped with graphitic, pyrrolic and pyridinic nitrogen species. Interestingly, the relative content of the nitrogen functionalities is controlled by the anion in the ionic liquid and its concentration, with the obtained graphene-based powders showing higher photocatalytic activity than GO. Furthermore, a remarkable synergistic effect is observed for GO-[bmim]-acetate powder (acting as co-catalyst) in combination with anatase TiO2 nanoparticles. The presented method opens new research avenues for the cost-effective mass production of graphene-based photocatalysts for water splitting applications.

Ugrinic, M.; Zambrano, A.; Berger, S.; Mann, S.; Tang, T.-Y. D.; deMello, A. Microfluidic Formation of Proteinosomes. Chemical Communications 2018, 54, 287–290

Herein we describe a novel microfluidic method for the generation of proteinosome micro-droplets, based on bovine serum albumin and glucose oxidase conjugated to PNIPAAm chains. The size of such water-in-oil droplets is regulated via control of the input reagent flow rate, with generated proteinosome populations exhibiting narrower size distributions than those observed when using standard bulk methodologies. Importantly, proteinosomes transferred from an oil- to an aqueous-environment remain intact, become fully hydrated and exhibit an increase in average size. Moreover, functional proteinosomes prepared via microfluidics exhibit lower Km values and higher enzymatic activities than proteinosomes produced by bulk methodologies.

Hoop, M.; Walde, C. F.; Riccò, R.; Mushtaq, F.; Terzopoulou, A.; Chen, X.-Z.; deMello, A. J.; Doonan, C. J.; Falcaro, P.; Nelson, B. J.; Puigmartí-Luis, J.; Pané, S. Biocompatibility characteristics of the metal organic framework ZIF-8 for therapeutical applications. Applied Materials Today 2018, 11, 13–21

Metal–organic frameworks (MOFs) are a class of crystalline materials constructed from organic linkers and inorganic nodes. MOFs typically possess ultra-high surface areas and pore volumes; thus, they are ideal candidates for biomedical applications. Zinc Imidazolate Framework 8 (ZIF-8) has been widely established in the literature as a potential candidate for on-demand drug delivery applications. Indeed, ZIF-8 has a remarkable loading capacity, stability in physiological environments, and tunable drug release properties. However, the use of ZIF-8 for in vivo applications requires a clear understanding of the interaction of ZIF-8 with biological tissue. In this work, we investigated the biocompatibility of ZIF-8 toward six different cell lines representing various body parts (kidney, skin, breast, blood, bones, and connective tissue). Our results suggest that ZIF-8 has no significant cytotoxicity up to a threshold value of 30 μg mL−1. Above 30 μg mL−1, the cytotoxicity is shown to result from the influence of released Zinc ions (Zn2+) on the mitochondrial ROS production. This adverse effect is responsible for cell cycle arrest in the G2/M phase due to irreversible DNA damage, ultimately initiating cellular apoptosis pathways. Due to this insight, we encapsulated a hormone, insulin, into ZIF-8 particles and then compared its drug delivery capabilities to the aforementioned cytotoxicity values. Our results suggest that ZIF-8 is suitable for therapeutic applications. Furthermore, this study establishes a clear understanding of the interaction of ZIF-8 and its constituents with various cell lines and highlights the important biocompatibility factors that must be considered for future in vivo testing.

2017

Yang, T.; Stavrakis, S.; deMello, A. A High-Sensitivity, Integrated Absorbance and Fluorescence Detection Scheme for Probing Picoliter-Volume Droplets in Segmented Flows. Analytical Chemistry 2017, 89, 12880–12887

Droplet-based microfluidic systems that incorporate flowing streams of pL-volume droplets surrounded by a continuous and immiscible carrier phase have attracted significant recent attention due to their utility in complex chemical and biological experimentation. Analysis of pL-droplets, generated at kHz frequencies and moving at high linear velocities, is almost exclusively achieved using fluorescence-based detection schemes. To extend the applicability of such optical detection schemes we herein report the development of a simple and cost-effective optofluidic platform ,integrating liquid core PDMS waveguides, that allows the accurate measurement of absorbance within individual pL-volume droplets moving within segmented flows. Using such an approach, differential measurements of “sample “and “reference” droplets can be acquired at 1 kHz and yields detection limits of 400 nM for fluorescein in water. Significantly, the presented technique enables simultaneous fluorescence and absorbance interrogation of rapidly moving droplets in a fully automated manner. Proof of principle is demonstrated through the titration and monitoring of pH gradients in real time.

Holzner, G.; Stavrakis, S.; deMello, A. Elasto-Inertial Focusing of Mammalian Cells and Bacteria Using Low Molecular, Low Viscosity PEO Solutions. Analytical Chemistry 2017, 89, 11653–11663

The ability to manipulate biological cells is critical in a diversity of biomedical and industrial applications. Microfluidic-based cell manipulations provide unique opportunities for sophisticated and high-throughput biological assays such as cell sorting, rare cell detection, and imaging flow cytometry. In this respect, cell focusing is an extremely useful functional operation preceding downstream biological analysis, since it allows the accurate lateral and axial positioning of cells moving through microfluidic channels, and thus enables sophisticated cell manipulations in a passive manner. Herein, we explore the utility of viscoelastic carrier fluids for enhanced elasto-inertial focusing of biological species within straight, rectangular cross section microfluidic channels. Since the investigated polymer solutions possess viscosities close to that of water and exhibit negligible shear thinning, focusing occurs over a wide range of elasticity numbers and a large range of Reynolds numbers. With a view to applications in the robust focusing of cells and bacteria, we assess and characterize the influence of accessible focusing parameters, including blockage ratio, volumetric flow rate, cell concentration, and polymer chain length.

Rane, A. S.; Rutkauskaite, J.; deMello, A.; Stavrakis, S. High-Throughput Multi-parametric Imaging Flow Cytometry. Chem 2017, 3, 588–602

Flow cytometry, incorporating either point- or imaging-based detection schemes, is recognized to be the gold-standard tool for high-throughput manipulation and analysis of single cells in flow but is typically limited in either the number of cells that can be interrogated per unit of time or the resolution with which individual cells can be imaged. To address these limitations, we present a sheathless, microfluidic imaging flow cytometer incorporating stroboscopic illumination for blur-free cellular analysis at throughputs exceeding 50,000 cells/s. By combining inertial focusing of cells in parallel microchannels and stroboscopic illumination, the chip-based cytometer is able to extract multi-color fluorescence, bright-field, and dark-field images and perform accurate sizing of individual cells and analysis of heterogeneous cell suspensions while maintaining operational simplicity. To showcase the efficacy of the approach, we apply the method to the rapid enumeration of apoptotic cells and the high-throughput discrimination of cell-cycle phases.

Weidenbacher, L.; Abrishamkar, A.; Rottmar, M.; Guex, A. G.; Maniura-Weber, K.; deMello, A. J.; Ferguson, S. J.; Rossi, R. M.; Fortunato, G. Electrospraying of microfluidic encapsulated cells for the fabrication of cell-laden electrospun hybrid tissue constructs. Acta Biomaterialia 2017, 64, 137–147

The fabrication of functional 3D tissues is a major goal in tissue engineering. While electrospinning is a promising technique to manufacture a structure mimicking the extracellular matrix, cell infiltration into elec- trospun scaffolds remains challenging. The robust and in situ delivery of cells into such biomimetic scaffolds would potentially enable the design of tissue engineered constructs with spatial control over cellular distri- bution but often solvents employed in the spinning process are problematic due to their high cytotoxicity. Herein, microfluidic cell encapsulation is used to establish a temporary protection vehicle for the in situ delivery of cells for the development of a fibrous, cell-laden hybrid biograft. Therefore a layer-by-layer process is used by alternating fiber electrospinning and cell spraying procedures.Both encapsulation and subsequent electrospraying of capsules has no negative effect on the viability and myogenic differentiation of murine myoblast cells. Propidium iodide positive stained cells were analyzed to quantify the amount of dead cells and the presence of myosin heavy chain positive cells after the processes was shown. Furthermore, encapsulation successfully protects cells from cytotoxic solvents (such as dimethyl- formamide) during in situ delivery of the cells into electrospun poly(vinylidene fluoride-co-hexafluoropropylene) scaffolds. The resulting cell-populated biografts demonstrate the clear potential of this approach in the creation of viable tissue engineering constructs.

Maceiczyk, R. M.; Hess, D.; Chiu, F. W. Y.; Stavrakis, S.; deMello, A. J. Differential detection photothermal spectroscopy: towards ultra-fast and sensitive label-free detection in picoliter & femtoliter droplets. Lab on a Chip 2017, 17, 3654–3663

Despite the growing importance of droplet-based microfluidics in high-throughput experimentation, few current methods allow the sensitive measurement of absorbance within rapidly moving droplets. To address this significant limitation, we herein present the application of differential detection photothermal interferometry (DDPI) for single-point absorbance quantification in pL- and fL-volume droplets. To assess the efficacy of our approach, we initially measure absorbance in 100 pL droplets at frequencies in excess of 1 kHz and determine a detection limit of 1.4 μmol L−1 for Erythrosin B (A = 3.8 × 10−4). Subsequently, we apply the method to the analysis of fL-volume droplets and droplets generated at frequencies in excess of 10 kHz. Finally, we demonstrate the utility of DDPI as a detection scheme for colorimetric assays. Specifically, we extract the Michaelis–Menten constant for the reaction of β-galactosidase and chlorophenol-red-β-D-galactopyranoside and monitor the metabolomic activity of a population of HL-60 cells at the single cell level. Results establish single-point absorbance detection as a powerful, sensitive and rapid alternative to fluorescence for a wide range of assays within segmented flows.

Maceiczyk, R. M.; Dümbgen, K.; Lignos, I.; Protesescu, L.; Kovalenko, M. V.; deMello, A. J. Microfluidic Reactors Provide Preparative and Mechanistic Insights into the Synthesis of Formamidinium Lead Halide Perovskite Nanocrystals. Chemistry of Materials 2017, 29, 8433–8439

Formamidinium lead bromide and iodide (FAPbX3, X = Br, I) in the form of colloidal nanocrystals (NCs) exhibit outstanding photoluminescence properties in the green and infrared regions of the electromagnetic spectrum, characterized by narrow emission line widths (below 90 meV) and high quantum yields (above 90%). The controlled formation of Br-I mixed halide NCs is a facile strategy for tuning band-gap energies, in particular between 700 and 800 nm, not accessible with CsPbX3 NCs. Herein, we report a mechanistic and high-throughput parametric screening study of the synthesis of such NCs using droplet-based microfluidic platforms, equipped with in situ optical characterization. We establish the growth conditions that fully suppress the formation of nanoplatelet impurities in the final colloid and demonstrate that the formation mechanism of FAPbBr3 NCs proceeds via the formation of nanoplatelets as transient species, whereas FAPbI3 forms directly as cubic-shaped NCs. In contrast to CsPb(Br/I)3 NCs, the stability of FAPb(Br/I)3 NCs increases with iodine content. Such NCs form by first nucleating pure FAPbI3 NCs, followed by incorporation of bromide ions.

Choi, N.; Lee, J.; Ko, J.; Jeon, J. H.; Rhie, G.; deMello, A. J.; Choo, J. An Integrated SERS-based Microdroplet Platform for the Automated Immunoassay of F1 Antigens in Yersinia pestis. Analytical Chemistry 2017, 89, 8413–8420

The development of surface-enhanced Raman scattering (SERS)-based microfluidic platforms has attracted significant recent attention in the biological sciences. SERS is a highly sensitive detection modality, with microfluidic platforms providing many advantages over microscale methods, including high analytical throughput, facile automation and reduced sample requirements. Accordingly, the integration of SERS with microfluidic platforms offers significant utility in chemical and biological experimentation. Herein, we report a fully integrated SERS-based microdroplet platform for the automatic immunoassay of specific antigen fraction 1 (F1) in Yersinia pestis. Specifically, highly efficient and rapid immunoreactions are achieved through sequential droplet generation, transport and merging, whilst wash-free immunodetection is real-ized through droplet-splitting. Such integration affords a novel multifunctional platform capable of performing complex multi-step immunoas-says in nL-volume droplets. The limit of detection of the F1 antigen for Yersinia pestis using the integrated SERS-based microdroplet platform is 59.6 pg/mL, a value approximately two orders of magnitude more sensitive than conventional enzyme-linked immunosorbent assays. This assay system has additional advantages including reduced sample consumption (less than 100 μL), rapid assay times (less than 10 minutes) and fully automated fluid control. We anticipate that this integrated SERS-based microdroplet device will provide new insights in the development of facile assay platforms for various hazardous materials.

Abrishamkar, A.; Rodríguez-San-Miguel, D.; Rodríguez Navarro, J. A.; Rodriguez-Trujillo, R.; Amabilino, D. B.; Mas-Ballesté, R.; Zamora, F.; deMello, A. J.; Puigmarti-Luis, J. Microfluidic-based Synthesis of Covalent Organic Frameworks (COFs): A Tool for Continuous Production of COF Fibers and Direct Printing on a Surface. Journal of Visualized Experiments 2017

Covalent Organic Frameworks (COFs) are a class of porous covalent materials which are frequently synthesized as unprocessable crystalline powders. The first COF was reported in 2005 with much effort centered on the establishment of new synthetic routes for its preparation.To date, most available synthetic methods for COF synthesis are based on bulk mixing under solvothermal conditions. Therefore, there is increasing interest in developing systematic protocols for COF synthesis that provide for fine control over reaction conditions and improve COF processability on surfaces, which is essential for their use in practical applications. Herein, we present a novel microfluidic-based method for COF synthesis where the reaction between two constituent building blocks, 1,3,5-benzenetricarbaldehyde (BTCA) and 1,3,5-tris(4- aminophenyl)benzene (TAPB), takes place under controlled diffusion conditions and at room temperature. Using such an approach yields sponge-like, crystalline fibers of a COF material, hereafter called MF-COF. The mechanical properties of MF-COF and the dynamic nature of the approach allow the continuous production of MF-COF fibers and their direct printing onto surfaces. The general method opens new potential applications requiring advanced printing of 2D or 3D COF structures on flexible or rigid surfaces.

Andrew deMello. Microfluidics for Ultra High-Throughput Experimentation: Droplets, Dots & Photons. Nobel Symposium 162, Stockholm, Sweden, 2017

The past 25 years have seen considerable progress in the development of microfabricated systems for use in the chemical and biological sciences. Interest in “microfluidic” technology has driven by concomitant advances in the areas of genomics, proteomics, nanoscale science, drug discovery, high-throughput screening and diagnostics, with a clearly defined need to perform rapid measurements on small sample volumes. At a fundamental level, microfluidic activities have been stimulated by the fact that physical processes can be more easily controlled when instrumental dimensions are reduced to the micron scale. The relevance of such technology is significant and characterized by an array of features that accompany system miniaturization. These features include the ability to process small volumes of fluid, enhanced analytical performance, reduced instrumental footprints, low unit costs, facile integration of functional components and the capacity to exploit atypical fluid behaviour to control chemical and biological entities in both time and space.

Ioannis Lignos, Richard Maceiczyk & Andrew J. deMello. Microfluidic Technology: Uncovering the Mechanisms of Nanocrystal Nucleation and Growth. Accounts of Chemical Research 2017, 50, 1248–1257

The controlled and reproducible formation of colloidal semiconductor nanocrystals (or quantum dots) is of central importance in nanoscale science and technology. The tunable size- and shape-dependent properties of such materials make them ideal candidates for the development of efficient and low-cost displays, solar cells, light-emitting devices, and catalysts. The formidable difficulties associated with the macroscale preparation of semi-conductor nanocrystals (possessing bespoke optical and chemical properties) result from the fact that underlying reaction mechanisms are complex and that the reactive environment is difficult to control. Automated microfluidic reactors coupled with monitoring systems and optimization algorithms aim to elucidate complex reaction mechanisms that govern both nucleation and growth of nanocrystals. Such platforms are ideally suited for the efficient optimization of reaction parameters, assuring the reproducible synthesis of nanocrystals with user-defined properties. This Account aims to inform the nanomaterials community about how microfluidic technologies can supplement flask experimentation for the ensemble investigation of formation mechanisms and design of semiconductor nanocrystals. We present selected studies outlining the preparation of quantum dots using microfluidic systems with integrated analytics. Such microfluidic reaction systems leverage the ability to extract real-time information regarding optical, structural, and compositional characteristics of quantum dots during nucleation and growth stages. The Account further highlights our recent research activities focused on the development and application of droplet-based microfluidics with integrated optical detection systems for the efficient and rapid screening of reaction conditions and a better understanding of the mechanisms of quantum dot synthesis. We describe the features and operation of fully automated microfluidic reactors and their subsequent application to high-throughput parametric screening of metal chalcogenides (CdSe, PbS, PbSe, CdSeTe), ternary and core/shell heavy metal-free quantum dots (CuInS2, CuInS2/ZnS), and all-inorganic perovskite nanocrystals (CsPbX3, X = Cl, Br, I) syntheses. Critically, concurrent absorption and photoluminescence measurements on millisecond to second time scales allow the extraction of basic parameters governing nanocrystal formation. Moreover, experimental data obtained from such microfluidic platforms can be directly supported by theoretical models of nucleation and growth. To this end, we also describe the use of metamodeling algorithms able to accurately predict optimized conditions of CdSe synthesis using a minimal number of sample parameters.Importantly, we discuss future challenges that must be addressed before microfluidic technologies are in a position to be widely adopted for the on-demand formation of nanocrystals. From a technology perspective, these challenges include the development of novel engineering platforms for the formation of complex architectures, the integration of monitoring systems able to harvest photophysical and structural information, the incorporation of continuous purification systems, and the application of optimization algorithms to multicomponent quantum dot systems.

Vigolo, D.; Zhao, J.; Handschin, S.; Cao, X.; deMello, A. J.; Mezzenga, R. Continuous Isotropic-Nematic Transition in Amyloid Fibril Suspensions Driven by Thermophoresis. Scientific Reports 2017, 7

The isotropic and nematic (I+N) coexistence for rod-like colloids is a signature of the first-order thermodynamics nature of this phase transition. However, in the case of amyloid fibrils, the biphasic region is too small to be experimentally detected, due to their extremely high aspect ratio. Herein, we study the thermophoretic behaviour of fluorescently labelled β-lactoglobulin amyloid fibrils, by inducing a temperature gradient across a microfluidic channel. We discover that fibrils accumulate towards the hot side of the channel at the temperature range studied, thus presenting a negative Soret coefficient. By exploiting this thermophoretic behaviour, we show that it becomes possible to induce a continuous I-N transition with the I and N phases at the extremities of the channel, starting from an initially single N phase, by generating an appropriate concentration gradient along the width of the microchannel. Accordingly, we introduce a new methodology to control liquid crystal phase transitions in anisotropic colloidal suspensions. Because the induced order-order transitions are achieved under stationary conditions, this may have important implications in both applied colloidal science, such as in separation and fractionation of colloids, as well as in fundamental soft condensed matter, by widening the accessibility of target regions in the phase diagrams.

Dressler, O. J.; Casadevall i Solvas, X.; deMello, A. J. Chemical and Biological Dynamics Using Droplet-Based Microfluidics. Annual Review of Analytical Chemistry 2017, 10, 1–24

Recent years have witnessed an increased use of droplet-based microfluidic techniques in a wide variety of chemical and biological assays. Nevertheless, obtaining dynamic data from these platforms has remained challenging, as this often requires reading the same droplets (possibly thousands of them) multiple times over a wide range of intervals (from milliseconds to hours). In this review, we introduce the elemental techniques for the formation and manipulation of microfluidic droplets, together with the most recent developments in these areas. We then discuss a wide range of analytical methods that have been successfully adapted for analyte detection in droplets. Finally, we highlight a diversity of studies where droplet-based microfluidic strategies have enabled the characterization of dynamic systems that would otherwise have remained unexplorable.

Ding, Y.; Choo, J.; deMello, A. J. From single-molecule detection to next-generation sequencing: microfluidic droplets for high-throughput nucleic acid analysis. Microfluidics and Nanofluidics 2017, 21

Droplet-based microfluidic technologies have proved themselves to be of significant utility in the performance of high-throughput chemical and biological experiments. By encapsulating and isolating reagents within femtoliter–nanoliter droplet, millions of (bio) chemical reactions can be processed in a parallel fashion and on ultra-short timescales. Recent applications of such technologies to genetic analysis have suggested significant utility in low-cost, efficient and rapid workflows for DNA amplification, rare mutation detection, antibody screening and next-generation sequencing. To this end, we describe and highlight some of the most interesting recent developments and applications of droplet-based microfluidics in the broad area of nucleic acid analysis. In addition, we also present a cursory description of some of the most essential functional components, which allow the creation of integrated and complex workflows based on flowing streams of droplets.

Chiu, D. T.; deMello, A. J.; Di Carlo, D.; Doyle, P. S.; Hansen, C.; Maceiczyk, R. M.; Wootton, R. C. R. Small but Perfectly Formed? Successes, Challenges, and Opportunities for Microfluidics in the Chemical and Biological Sciences. Chem 2017, 2, 201–223

Microfluidic systems are pervasive in many areas of experimental science, but what are the real advantages of this technology? We describe some of the fea- tures and properties that make microfluidic devices unique experimental tools. In addition to pointing out some of the less effective uses of this technology, we assess the most successful applications of microfluidics over the last two de- cades and highlight the areas where they had the greatest impact. We also pro- pose applications where microfluidic systems could be applied to the greatest effect in the future.

Maceiczyk, R.; Shimizu, H.; Müller, D.; Kitamori, T.; deMello, A. A Photothermal Spectrometer for Fast and Background-Free Detection of Individual Nanoparticles in Flow. Analytical Chemistry 2017, 89, 1994–1999

Sensitive detection and quantification of individual plasmonic nanoparticles is critical in a range of applications in the biological, nanomaterials, and analytical sciences. Although a wide range of techniques can be applied to the analysis of immobilized particles, high-throughput analysis of nanoscale species in flow is surprisingly underdeveloped. To address this shortcoming, we present an ultrasensitive, background-free technique based on the photothermal effect and termed differential detection photothermal interferometry (DDPI). We show, both theoretically and experimentally, that DDPI can specifically extract either the phase or amplitude of a photothermal signal. We then quantitatively detect 10 and 20 nm diameter gold nanoparticles at femtomolar concentrations and at linear flow speeds of 10 mm/s. In the case of 50 nm gold particles, we operate at an even higher linear flow speed of 100 mm/s, corresponding to an analyzed volume of more than 1 nL/s. This allows quantification of particle content at attomolar to femtomolar concentrations and counting rates between 0.1 and 400 particles per second. Finally, we confirm that the signal follows the size-dependent variations predicted by Mie theory.

2016

Choi, J.-W.; Jo, B.-G.; deMello, A. J.; Choo, J.; Kim, H. Y. Streptavidin-triggered signal amplified fluorescence polarization for analysis of DNA-protein interaction. The Analyst 2016, 141, 6499–6502

Fluorescence polarization (FP) is a sensitive, robust, and homogeneous assay format, able to probe a diversity of biological molecules and their interactions. Herein, we describe a new FP strategy based on the use of streptavidin as a signal amplifier. Such signal amplified fluorescence polarization (SAFP) was used to monitor the binding affinity of human angiogenin and a single-stranded DNA aptamer. Streptavidin was bound to a biotinylated single-stranded DNA aptamer and the interaction between this complex and Alexa Fluor 488 labelled human angiogenin was measured. A dissociation constant of 135.3 ± 32.9 nM and a limit of detection of 6.3 nM were successfully extracted only when the FP signal was increased (without binding hindrance) via streptavidin. Moreover, the demonstrated approach was specific to target molecules without any non-specific binding. The streptavidin-triggered SAFP method unlike amplification strategies that utilize nanomaterials (such as graphene oxides, carbon nanotubes, and metal nanoparticles) is not compromised by fluorescence quenching, and it is able to operate within nanomolar concentration regimes. Furthermore, unlike the other FP signal amplification strategies that use dual binding DNA probes, the presented method is simple to implement with signal amplification only requiring the binding of streptavidin with biotinylated DNA. This method could be expanded to analyze molecular interactions and it may be a useful tool for FP measurement by reducing the concentration of rare and expensive protein samples.

Casadevall i Solvas, X.; deMello, A. Particle concentration influences inertial focusing in Multiorifice Flow Fractionation microfluidic devices. Matters 2016

Multiorifice Flow Fractionation (MOFF) devices have been used for the separation of microparticles and cells according to their size and the degree of inertia (i.e. Re number). Herein an additional parameter, particle concentration, is reported to affect the performance of MOFF when the remaining conditions are unchanged. Particularly, at low concentrations focusing occurs efficiently at the center of these devices, while at higher concentrations particles tend to accumulate near the channel walls. This indicates that particle-particle interactions are a key component in the performances of these devices.

Bawazer, L. A.; McNally, C. S.; Empson, C. J.; Marchant, W. J.; Comyn, T. P.; Niu, X.; Cho, S.; McPherson, M. J.; Binks, B. P.; deMello, A.; Meldrum, F. C. Combinatorial microfluidic droplet engineering for biomimetic material synthesis. Science Advances 2016, 2, e1600567–e1600567

Although droplet-based systems are used in a wide range of technologies, opportunities for systematically customizing their interface chemistries remain relatively unexplored. This article describes a new microfluidic strategy for rapidly tailoring emulsion droplet compositions and properties. The approach uses a simple platform for screening arrays of droplet-basedmicrofluidic devices and couples thiswith combinatorial selection of the droplet compositions. Through the application of genetic algorithms over multiple screening rounds, droplets with target properties can be rapidly generated. The potential of this method is demonstrated by creating droplets with enhanced stability, where this is achieved by selecting carrier fluid chemistries that promote titanium dioxide formation at the droplet interfaces. The interface is a mixture of amorphous and crystalline phases, and the resulting composite droplets are biocompatible, supporting in vitro protein expression in their interiors. This general strategy will find widespread application in advancing emulsion properties for use in chemistry, biology, materials, and medicine.

Rubio-Martinez, M.; Imaz, I.; Domingo, N.; Abrishamkar, A.; Mayor, T. S.; Rossi, R. M.; Carbonell, C.; deMello, A. J.; Amabilino, D. B.; Maspoch, D.; Puigmartí-Luis, J. Freezing the Nonclassical Crystal Growth of a Coordination Polymer Using Controlled Dynamic Gradients. Advanced Materials 2016, 28, 8150–8155

Manually engineered self-assembled structures have for many years been investigated under equilibrium conditions so that their most stable forms are reached, until recently. There has been a growing interest in obtaining and studying non-equilibrium self-assembled structures. The primary reason for this is that non-equilibrium structures (which are typically formed transiently under a constant influx of energy) can offer a broad number of intriguing opportunities in the development of novel materials and systems with advanced functionalities. For example, transient and/or steady-state self-assembled structures generated far from equilibrium are the basis of many sophisticated functions observed in living systems, e.g. DNA replication and/or cell division. Nonetheless, the controlled synthesis and study of intermediate, self-assembled structures is still a major challenge, which currently limits advancements in materials development and technology. Herein we show for first time a methodology that can be efficiently used to synthesize, isolate and study out-of-equilibrium crystal structures employing controlled and diffusion limited microfluidic environments. Unlike studies conducted with conventional mixing procedures in a flask, we prove experimentally and with numerical simulations that microfluidic technologies can undoubtedly fine-tune reaction times and reagents concentration profiles; factors that enable obtaining out of-equilibrium self-assembled crystal forms.

Yashina, A.; Lignos, I.; Stavrakis, S.; Choo, J.; deMello, A. J. Scalable production of CuInS2/ZnS quantum dots in a two-step droplet-based microfluidic platform. Journal of Materials Chemistry C 2016, 4, 6401–6408

We report the scalable formation of CuInS2/ZnS nanocrystals using a two-stage microfluidic reactor integrated with a real-time optical detection system, which is able to monitor reaction parameters prior and subsequent to the addition of the shell material. By injecting a ZnS single source precursor in droplets containing CuInS2 cores and without the need of purification steps, we are able to obtain core-shell nanocrystal populations emitting between 580 and 760 nm with significant narrower size distributions (90–95 nm) than for the same material systems synthesized on the macroscale. In-line monitoring allowed for rapid assessment of optimum reaction parameters (Cu/In, S/(Cu+In), Zn/(Cu+In) molar ratios, temperatures and reaction time) and enabled the formation of CuInS2/ZnS nanocrystals with high photoluminescence quantum yields (∼ 55%) within a few seconds. We believe that this synthetic methodology will be of significant utility in controllable production of ternary and quaternary metal chalcogenides, complex core-shell and doped nanostructures.

Martino, C.; deMello, A. J. Droplet-based microfluidics for artificial cell generation: a brief review. Interface Focus 2016, 6, 20160011

Artificial cells are best defined as micrometre-sized structures able to mimic many of the morphological and functional characteristics of a living cell. In this mini-review, we describe progress in the application of droplet-based microfluidics for the generation of artificial cells and protocells.

Maceiczyk, R. M.; Bezinge, L.; deMello, A. J. Kinetics of nanocrystal synthesis in a microfluidic reactor: theory and experiment. Reaction Chemistry & Engineering 2016, 1, 261–271

The processes occurring during nanocrystal nucleation and growth are currently not well understood. Herein, we theoretically and experimentally investigate the growth kinetics in colloidal nanocrystal synthesis. Using a novel microfluidic reactor integrating independent modules for nucleation and growth, we demonstrate the controlled, direct synthesis of high quality nanocrystals in high yield. For CdSe nanocrystals, we find that size tuning solely by variation of the reaction time and temperature does not yield product populations of optimal size dispersion or yield. Instead, we present an improved method for the synthesis of bespoke nanocrystals that relies on the controlled addition of precise amounts of additional precursor subsequent to nucleation and fine tuning of the reaction time and temperature in the second stage. Real-time spectroscopic monitoring of the produced crystals in conjunction with kinetic simulations confirms the close correspondence between the model and the experiment and elegantly quantifies the effects of temperature, concentration, additives and surfactants on conversion, growth and diffusion rates within the model framework. We show that the conversion of the precursor to a monomer follows a first order rate law and that the growth rate has a stronger temperature dependence than the conversion rate. Moreover, the surfactant concentration retards the reaction by inhibiting diffusion to the growing crystals whilst maintaining a uniform conversion rate. Finally, we demonstrate that diphenylphosphine, a common additive in CdSe synthesis, enhances the reaction rate by accelerating precursor conversion.
» REACTION CHEMISTRY AND ENGINEERING COVER 2016

Martino, C.; Vigolo, D.; Solvas, X. C. i; Stavrakis, S.; deMello, A. J. Real-Time PEGDA-Based Microgel Generation and Encapsulation in Microdroplets. Advanced Materials Technologies 2016, 1, 1600028

Herein, a method is reported that combines droplet-based microfluidics and microscope projection photolithography for the generation of poly ethylene glycol diacrylate microgels and their encapsulation within pL-volume droplets. By implementing continuous-flow photolithography in the vicinity of a cross junction, the real-time generation and in situ encapsulation of fiber-like structures within pL-volume aqueous microdroplets is demonstrated. The effect of UV excitation is assessed at varying distances from the cross junction for both constant and pulsed UV excitation modes, as a route to controlling microfiber length. Finally, UV excitation within trapped droplets is explored and how the combination of the two techniques can lead to the generation of 3D patterned microstructures is demonstrated, opening new avenues for the rapid generation of inner scaffolding of artificial cell facsimiles.

Andrew deMello, John Rogers & Zhong Lin Wang. Advanced Materials Technologies — When a Material really is a Material. Advanced Materials Technologies 2016, 1

The first articles in the newest journal in the Advanced Materials family have been published. The work appearing in Advanced Materials Technologies will have an emphasis on device design, integration, configuration, optimization, and function, rather than on the materials themselves.

Müller, D.; Cattaneo, S.; Meier, F.; Welz, R.; de Vries, T.; Portugal-Cohen, M.; Antonio, D. C.; Cascio, C.; Calzolai, L.; Gilliland, D.; de Mello, A. Inverse supercritical fluid extraction as a sample preparation method for the analysis of the nanoparticle content in sunscreen agents. Journal of Chromatography A 2016, 1440, 31–36

We demonstrate the use of inverse supercritical carbon dioxide (scCO2) extraction as a novel method of sample preparation for the analysis of complex nanoparticle-containing samples, in our case a model sunscreen agent with titanium dioxide nanoparticles. The sample was prepared for analysis in a simplified process using a lab scale supercritical fluid extraction system. The residual material was easily dispersed in an aqueous solution and analyzed by Asymmetrical Flow Field-Flow Fractionation (AF4) hyphenated with UV- and Multi-Angle Light Scattering detection. The obtained results allowed an unambiguous determination of the presence of nanoparticles within the sample, with almost no background from the matrix itself, and showed that the size distribution of the nanoparticles is essentially maintained. These results are especially relevant in view of recently introduced regulatory requirements concerning the labeling of nanoparticle-containing products. The novel sample preparation method is potentially applicable to commercial sunscreens or other emulsion-based cosmetic products and has important ecological advantages over currently used sample preparation techniques involving organic solvents.

Cao, X.; deMello, A. J.; Elvira, K. S. Enhanced versatility of fluid control on centrifugal microfluidic platforms using two degrees of freedom. Lab on a Chip 2016, 16, 1197–1205

Centrifugal microfluidic platforms have significant potential in commercial applications because of their operational flexibility and minimal external infrastructure requirements. However, the dynamic and real-time control of fluid flow within traditional centrifugal microfluidic platforms is problematic. To address this significant limitation, we propose a two degrees of freedom platform, in which a digital servo is located at each end of an arm driven by a motor. This allows for reversible inward pumping between multiple chambers with perfect efficiency. Furthermore, the addition of a second degree of freedom allows position-based pressure controlled burst valves to be accessed and operated in an independent fashion. To demonstrate the efficacy of this technical innovation, we show rapid and configurable flow switching between three target chambers within a centrifugal microfluidic device.

Ding, Y.; Qiu, F.; Casadevall i Solvas, X.; Chiu, F.; Nelson, B.; deMello, A. Microfluidic-Based Droplet and Cell Manipulations Using Artificial Bacterial Flagella. Micromachines 2016, 7, 25

Herein, we assess the functionality of magnetic helical microswimmers as basic tools for the manipulation of soft materials, including microdroplets and single cells. Their ability to perform a range of unit operations is evaluated and the operational challenges associated with their use are established. In addition, we also report on interactions observed between the head of such helical swimmers and the boundaries of droplets and cells and discuss the possibilities of assembling an artificial swimming microorganism or a motorized cell.

Lignos, I.; Stavrakis, S.; Nedelcu, G.; Protesescu, L.; deMello, A. J.; Kovalenko, M. V. Synthesis of Cesium Lead Halide Perovskite Nanocrystals in a Droplet-Based Microfluidic Platform: Fast Parametric Space Mapping. Nano Letters 2016, 16, 1869–1877

Prior to this work, fully inorganic nanocrystals of cesium lead halide perovskite (CsPbX3, X = Br, I and Cl and Cl/Br and Br/I mixed halide systems), exhibiting bright and tunable photoluminescence, have been synthesized using conventional batch (flask-based) reactions. Unfortunately, our understanding of the parameters governing the formation of these nanocrystals is still very limited due to extremely fast reaction kinetics and multiple variables involved in ion-metathesis-based synthesis of such multinary halide systems. Herein, we report the use of a droplet-based microfluidic platform for the synthesis of CsPbX3 nanocrystals. The combination of online photoluminescence and absorption measurements and the fast mixing of reagents within such a platform allows the rigorous and rapid mapping of the reaction parameters, including molar ratios of Cs, Pb and halide precursors, reaction temperatures and reaction times. This translates into enormous savings in reagent usage and screening times when compared to analogous batch synthetic approaches. The early-stage insight into the mechanism of nucleation of metal halide nanocrystals suggests similarities with multinary metal chalcogenide systems, albeit with much faster reaction kinetics in the case of halides. Furthermore, we show that microfluidics-optimized synthesis parameters are also directly transferrable to the conventional flask-based reaction.

Gao, R.; Cheng, Z.; deMello, A. J.; Choo, J. Wash-free magnetic immunoassay of the PSA cancer marker using SERS and droplet microfluidics. Lab on a Chip 2016, 16, 1022–1029

We report a novel wash-free magnetic immunoassay technique for prostate-specific antigen (PSA) that uses a surface-enhanced Raman scattering (SERS)-based microdroplet sensor. The magnetic bar embedded in a droplet-based microfluidic system segregates the free and bound SERS tags by splitting the droplets into two smaller parts. The presence of PSA targets leads more SERS tags to immunocomplex in one droplet so that fewer SERS tags remain in another supernatant solution droplet. Thus, SERS signal measurement enables the quantitative evaluation of PSA markers. This approach can provide a rapid and sensitive assay that is applicable for PSA cancer markers in serum without any washing. Specifically, SERS signals were measured at 174 droplets per minute and averaged for quantitative evaluation of PSA. The limit of detection (LOD) determined by our SERS-based microdroplet sensor was estimated to be below 0.1 ng mL−1, which is significantly below the clinical cut-off value for the diagnosis of prostate cancer. In addition, because the entire assay can be carried out automatically, only a minimal amount of sample is needed. Accordingly, the approach is expected to be useful as a potential clinical tool for the early diagnosis of prostate cancer.

Abrishamkar, A.; Paradinas, M.; Bailo, E.; Rodriguez-Trujillo, R.; Pfattner, R.; Rossi, R. M.; Ocal, C.; deMello, A. J.; Amabilino, D. B.; Puigmartí-Luis, J. Microfluidic Pneumatic Cages: A novel approach for in-chip crystal trapping, manipulation and controlled chemical treatment. Journal of Visualized Experiments 2016

The precise localization and controlled chemical treatment of structures on a surface are significant challenges for common laboratory technologies. Herein, we introduce a microfluidic-based technology, employing a double-layer microfluidic device, which can trap and localize in situ and ex situ synthesized structures on microfluidic channel surfaces. Crucially, we show how such a device can be used to conduct controlled chemical reactions onto on-chip trapped structures and we demonstrate how the synthetic pathway of a crystalline molecular material and its positioning inside a microfluidic channel can be precisely modified with this technology. This approach provides new opportunities for the controlled assembly of structures on surface and for their subsequent treatment.

Martino, C.; Statzer, C.; Vigolo, D.; deMello, A. J. Controllable Generation and Encapsulation of Alginate Fibers Using Droplet-Based Microfluidics. Lab on a Chip 2016, 16, 59–64

Herein we demonstrate the segmentation of alginate solution streams to generate alginate fibers of precisely controllable lengths between 200 and 1000 μm. Moreover, we demonstrate the subsequent encapsulation of the formed fibers within pL-volume microdroplets, produced within the same microfluidic device, in a direct manner. Finally, we show immediate and complete on- chip gelation of alginate fibers in a rapid and reproducible fashion.

Stanley, C. E.; Grossmann, G.; Casadevall i Solvas, X.; deMello, A. J. Soil-on-a-Chip: Microfluidic platforms for environmental organismal studies. Lab on a Chip 2016, 16, 228–241

Soil is the habitat of countless organisms and encompasses an enormous variety of dynamic environmental conditions. While it is evident that a thorough understanding of how organisms interact with the soil environment may have substantial ecological and economical impact, current laboratory-based methods depend on reductionist approaches that are incapable of simulating natural diversity. The application of Lab-on-a-Chip or microfluidic technologies to organismal studies is an emerging field, where the unique benefits afforded by system miniaturisation offer new opportunities for the experimentalist. Indeed, precise spatiotemporal control over the microenvironments of soil organisms in combination with high-resolution imaging has the potential to provide an unprecedented view of biological events at the single-organism or single-cell level, which in turn opens up new avenues for environmental and organismal studies. Herein we review some of the most recent and interesting developments in microfluidic technologies for the study of soil organisms and their interactions with the environment. We discuss how so-called “Soil-on-a-Chip” technology has already contributed significantly to the study of bacteria, nematodes, fungi and plants, as well as inter-organismal interactions, by advancing experimental access and environmental control. Most crucially, we highlight where distinct advantages over traditional approaches exist and where novel biological insights will ensue.

Choi, J.-W.; Min, K.-M.; Hengoju, S.; Kim, G.-J.; Chang, S.-I.; deMello, A. J.; Choo, J.; Kim, H. Y. A droplet-based microfluidic immunosensor for high efficiency melamine analysis. Biosensors and Bioelectronics 2016, 80, 182–186

We report a droplet-based microfluidic immunosensor for the rapid and accurate detection of melamine, an organic base that has been implicated in widescale adulteration of food products such as milk. Our melamine assay is based on the competitive reaction between native melamine and a melamine-fluorescein isothiocyanate (FITC) conjugate against an anti-hapten antibody. The adoption of fluorescence polarization, allows the quantification of melamine in a more direct and rapid manner than established heterogeneous methods based on liquid chromatography, mass spectrometry, and enzyme-linked immunosorbent assay (ELISA). The detection protocol provides a limit of detection of 300 ppb, which is below the maximum allowable melamine levels (2.5 ppm) defined by the U.S. Food and Drug Administration and the European Commission to a significant extent.

2015

Kang, D.-K.; Gong, X.; Cho, S.; Kim, J.; Edel, J. B.; Chang, S.-I.; Choo, J.; deMello, A. J. 3D Droplet Microfluidic Systems for High-Throughput Biological Experimentation. Analytical Chemistry 2015, 87, 10770–10778

Herein, we describe the development of a multilayer droplet microfluidic system for creating concentration gradients and generating microdroplets of varying composition for high-throughput biochemical and cell-based screening applications. The 3D droplet-based microfluidic device consists of multiple PDMS layers, which are used to generate logarithmic concentration gradient reagent profiles. Parallel flow focusing structures are used to form picoliter-sized droplets of defined volumes but of varying composition. As proof of concept, we demonstrate rapid enzymatic activity assays and drug cytotoxicity assays on bacteria. The 3D droplet-based microfluidic platform has the potential to allow for high-efficiency and high-throughput analysis, overcoming the structural limitations of single layer microfluidic systems.

Chon, H.; Wang, R.; Lee, S.; Bang, S.-Y.; Lee, H.-S.; Bae, S.-C.; Hong, S. H.; Yoon, Y. H.; Lim, D. W.; deMello, A. J.; Choo, J. Clinical validation of surface-enhanced Raman scattering-based immunoassays in the early diagnosis of rheumatoid arthritis. Analytical and Bioanalytical Chemistry 2015, 407, 8353–8362

We assess the clinical feasibility of surface-enhanced Raman scattering (SERS) based immunoassays in the early diagnosis of rheumatoid arthritis (RA). Specifically, an autoantibody against citrullinated peptide (anti-CCP) is used as a biomarker, magnetic beads conjugated with CCP used as substrates and anti-human IgG-conjugated HGNs used as SERS nano-tags. Anti-CCP serum levels are successfully determined by monitoring characteristic Raman intensities of the SERS nano-tags. At high concentrations of anti-CCP (>25 U/mL), levels determined using the SERS assay are consistent with those obtained via an ELISA-based assay. Nevertheless, quantitation via our SERS-based assay is significantly more accurate at low concentrations (<25 U/mL). Anti-CCP assays are performed on 74 clinical blood samples, using both the SERS-based assay and a commercial ELISA kit. Results demonstrate a good correlation between the ELISA and SERS-based assays in the anti-CCP positive group (n=31, >25 U/mL). However, in the anti-CCP negative group (n=43, <25 U/mL), the SERS-based assay is shown to be more reproducible. Accordingly, we suggest that SERS-based assays are potentially novel and useful tools in the early diagnosis of RA.

Chiu, F. W. Y.; Bagci, H.; Fisher, A. G.; deMello, A. J.; Elvira, K. S. A microfluidic toolbox for cell fusion. Journal of Chemical Technology & Biotechnology 2016, 91, 16–24

Cellular fusion is a key process in many fields ranging from historical gene mapping studies and monoclonal antibody production, through to cell reprogramming. Traditional methodologies for cell fusion rely on the random pairing of different cell types and generally result in low and variable fusion efficiencies. These approaches become particularly limiting where substantial numbers of bespoke one-to-one fusions are required, for example for in-depth studies of nuclear reprogramming mechanisms. In recent years, microfluidic technologies have proven valuable in creating platforms where the manipulation of single cells is highly efficient, rapid and controllable. These technologies also allow the integration of different experimental steps and characterisation processes into a single platform. Although the application of microfluidic methodologies to cell fusion studies is promising, current technologies that rely on static trapping are limited both in terms of the overall number of fused cells produced and their experimental accessibility. Here we review some of the most exciting breakthroughs in core microfluidic technologies that will allow the creation of integrated platforms for controlled cell fusion at high throughput.

Collins, D. J.; Neild, A.; deMello, A.; Liu, A.-Q.; Ai, Y. The Poisson distribution and beyond: methods for microfluidic droplet production and single cell encapsulation. Lab on a Chip 2015, 15, 3439–3459

In recent years there has been an explosion of methods for encapsulating cells in droplets. This review examines the state-of-the-art, including methods for active encapsulation.

Müller, D.; Cattaneo, S.; Meier, F.; Welz, R.; de Mello, A. J. Nanoparticle separation with a miniaturized asymmetrical flow field-flow fractionation cartridge. Frontiers in Chemistry 2015, 3

Asymmetrical Flow Field-Flow Fractionation (AF4) is a separation technique applicable to particles over a wide size range. Despite the many advantages of AF4, its adoption in routine particle analysis is somewhat limited by the large footprint of currently available separation cartridges, extended analysis times and significant solvent consumption. To address these issues, we describe the fabrication and characterization of miniaturized AF4 cartridges. Key features of the down-scaled platform include simplified cartridge and reagent handling, reduced analysis costs and higher throughput capacities. The separation performance of the miniaturized cartridge is assessed using certified gold and silver nanoparticle standards. Analysis of gold nanoparticle populations indicates shorter analysis times and increased sensitivity compared to conventional AF4 separation schemes. Moreover, nanoparticulate titanium dioxide populations exhibiting broad size distributions are analyzed in a rapid and efficient manner. Finally, the repeatability and reproducibility of the miniaturized platform are investigated with respect to analysis time and separation efficiency.

Dora. Tang, T.-Y.; van Swaay, D.; deMello, A.; Ross Anderson, J. L.; Mann, S. In vitro gene expression within membrane-free coacervate protocells. Chemical Communications 2015, 51, 11429–11432

Cell-free gene expression of a fluorescent protein (mCherry) is demonstrated within the molecularly crowded matrix of a polysaccharide/polypeptide coacervate.

van Swaay, D.; Tang, T.-Y. D.; Mann, S.; de Mello, A. Microfluidic Formation of Membrane-Free Aqueous Coacervate Droplets in Water. Angewandte Chemie International Edition 2015, 54, 8398–8401

We report on the formation of coacervate droplets from poly(diallyldimethylammonium chloride) with either adenosine triphosphate or carboxymethyl-dextran using a microfluidic flow-focusing system. The formed droplets exhibit improved stability and narrower size distributions for both coacervate compositions when compared to the conventional vortex dispersion techniques. We also demonstrate the use of two parallel flow-focusing channels for the simultaneous formation and co-location of two distinct populations of coacervate droplets containing different DNA oligonucleotides, and that the populations can coexist in close proximity up to 48 h without detectable exchange of genetic information. Our results show that the observed improvements in droplet stability and size distribution may be scaled with ease. In addition, the ability to encapsulate different materials into coacervate droplets using a microfluidic channel structure allows for their use as cell-mimicking compartments.

Lignos, I.; Stavrakis, S.; Kilaj, A.; deMello, A. J. Millisecond-Timescale Monitoring of PbS Nanoparticle Nucleation and Growth Using Droplet-Based Microfluidics. Small 2015, 11, 4009–4017

The early-time kinetics (<1 s) of lead sulfide (PbS) quantum dot formation are probed using a novel droplet-based microfluidic platform, which allows for high-throughput and real-time optical analysis of the reactive process with millisecond time resolution. The reaction platform enables the concurrent investigation of the emission characteristics of PbS quantum dots and a real-time estimation of their size and concentration during nucleation and growth. These investigations reveal a two-stage mechanism for PbS nanoparticle formation. The first stage corresponds to the fast conversion of precursor species to PbS crystals, followed by the growth of the formed particles. The growth kinetics of the PbS nanoparticles follow the Lifshitz–Slyozov–Wagner model for Ostwald ripening, allowing direct estimation of the rate constants for the process. In addition, the extraction of absorption spectra of ultrasmall quantum dots is demonstrated for first time in an online manner. The droplet-based microfluidic platform integrated with online spectroscopic analysis provides a new tool for the quantitative extraction of high temperature kinetics for systems with rapid nucleation and growth stages.

Dressler, O. J.; Yang, T.; Chang, S.-I.; Choo, J.; Wootton, R. C. R.; deMello, A. J. Continuous and low error-rate passive synchronization of pre-formed droplets. RSC Advances 2015, 5, 48399–48405

A microfluidic droplet-handling architecture for the synchronization of asynchronous, mis-matched, pre-formed droplet streams is demonstrated. This architecture is shown to be robust to variations in droplet input frequencies, whilst still producing highly reliable synchronisation. The operational phase space with regards to droplet size disparity is explored and the long-term operational stability of the system confirmed. Specifically, the microfluidic platform to synchronise droplet streams at a rate of 33 Hz over extended periods of time and with an error rate less than 0.2%.
» Continuous synchronisation of droplets

Poulsen, C. E.; Wootton, R. C. R.; Wolff, A.; deMello, A. J.; Elvira, K. S. A microfluidic platform for the rapid determination of distribution coefficients by gravity assisted droplet-based liquid-liquid extraction. Analytical Chemistry 2015, 87, 6265–6270

The determination of pharmacokinetic properties of drugs, such as the distribution coefficient (D) is a crucial measurement in pharmaceutical research. Surprisingly, the conventional (gold standard) technique used for D measurements, the shake-flask method, is antiquated and unsuitable for the testing of valuable and scarce drug candidates. Herein, we present a simple microfluidic platform for the determination of distribution coefficients using droplet-based liquid–liquid extraction. For simplicity, this platform makes use of gravity to enable phase separation for analysis and is 48 times faster and uses 99% less reagents than performing an equivalent measurement using the shake-flask method. Furthermore, the D measurements achieved in our platform are in good agreement with literature values measured using traditional shake-flask techniques. Since D is affected by volume ratios, we use the apparent acid dissociation constant, pK′, as a proxy for intersystem comparison. Our platform determines a pK′ value of 7.24 ± 0.15, compared to 7.25 ± 0.58 for the shake-flask method in our hands and 7.21 for the shake-flask method in the literature. Devices are fabricated using injection molding, the batchwise fabrication time is <2 min per device (at a cost of $1 U.S. per device), and the interdevice reproducibility is high.

Gao, R.; Ko, J.; Cha, K.; Ho Jeon, J.; Rhie, G.; Choi, J.; deMello, A. J.; Choo, J. Fast and sensitive detection of an anthrax biomarker using SERS-based solenoid microfluidic sensor. Biosensors and Bioelectronics 2015, 72, 230–236

We report the application of a fully automated surface-enhanced Raman scattering (SERS)-based solenoid-embedded microfluidic device to the quantitative and sensitive detection of anthrax biomarker poly-γ-d-glutamic acid (PGA) in solution. Analysis is based on the competitive reaction between PGA and PGA-conjugated gold nanoparticles with anti-PGA-immobilized magnetic beads within a microfluidic environment. Magnetic immunocomplexes are trapped by yoke-type solenoids embedded within the device, and their SERS signals were directly measured and analyzed. To improve the acccuracy of measurement process, external standard values for PGA-free serum were also measured through use of a control channel. This additional measurement greatly improves the reliability of the assay by minimizing the influence of extraneous experimental variables. The limit of detection (LOD) of PGA in serum, determined by our SERS-based microfluidic sensor, is estimated to be 100 pg/mL. We believe that the defined method represents a valuable analytical tool for the detection of anthrax-related aqueous samples.

Hess, D.; Rane, A.; deMello, A. J.; Stavrakis, S. High-Throughput, Quantitative Enzyme Kinetic Analysis in Microdroplets using Stroboscopic Epifluorescence Imaging. Analytical Chemistry 2015, 87, 4965–4972

Droplet-based microfluidic systems offer a range of advantageous features for the investigation of enzyme kinetics, including high time resolution and the ability to probe extremely large numbers of discrete reactions while consuming low sample volumes. Kinetic measurements within droplet-based microfluidic systems are conventionally performed using single point detection schemes. Unfortunately, such an approach prohibits the measurement of an individual droplet over an extended period of time. Accordingly, we present a novel approach for the extensive characterization of enzyme–inhibitor reaction kinetics within a single experiment by tracking individual and rapidly moving droplets as they pass through an extended microfluidic channel. A series of heterogeneous and pL-volume droplets, containing varying concentrations of the fluorogenic substrate resorufin β-d-galactopyranoside and a constant amount of the enzyme β-galactosidase, is produced at frequencies in excess of 150 Hz. By stroboscopic manipulation of the excitation laser light and adoption of a dual view detection system, “blur-free” images containing up to 150 clearly distinguishable droplets per frame are extracted, which allow extraction of kinetic data from all formed droplets. The efficiency of this approach is demonstrated via a Michaelis–Menten analysis which yields a Michaelis constant, Km, of 353 μM. Additionally, the dissociation constant for the competitive inhibitor isopropyl β-d-1-thiogalactopyranoside is extracted using the same method.

Pirbodaghi, T.; Vigolo, D.; Akbari, S.; deMello, A. Investigating the fluid dynamics of rapid processes within microfluidic devices using bright-field microscopy. Lab on a Chip 2015, 15, 2140–2144

The widespread application of microfluidic devices in the biological and chemical sciences requires the implementation of complex designs and geometries, which in turn leads to atypical fluid dynamic phenomena. Accordingly, a complete understanding of fluid dynamics in such systems is key in the facile engineering of novel and efficient analytical tools. Herein, we present an inexpensive and accurate approach for studying the fluid dynamics of rapid processes within microfluidic devices using bright-field microscopy with white light illumination. Specifically, we combine Ghost Particle Velocimetry and the detection of moving objects in automated video surveillance to track submicron size tracing particles via cross correlation between the speckle patterns of successive images. The efficacy of the presented technique is demonstrated by measuring the flow field over a square pillar (80 μm × 80 μm) in a 200 μm wide microchannel at high volumetric flow rates. Experimental results are in excellent agreement with those obtained via computational fluid dynamics simulations. The method is subsequently used to study the dynamics of droplet generation at a flow focusing microfluidic geometry. A unique feature of the presented technique is the ability to perform velocimetry analysis of ultra high-speed phenomena, which is not possible using micron-resolution particle image velocimetry (μPIV) approaches based on confocal or fluorescence microscopy.

Martino, C.; Lee, T. Y.; Kim, S.-H.; deMello, A. J. Microfluidic Generation of PEG-b-PLA Polymersomes Containing Alginate-based Core Hydrogel. Biomicrofluidics 2015, 9, 024101

Herein, we demonstrate a novel method for the generation of monodisperse cell-like structures containing a biocompatible hydrogel matrix surrounded by a membrane responsive to chemical cues. Specifically, we employ droplet-based microfluidics to generate PEG-PLA polymersomes encapsulating alginate in liquid form. We investigate alginate core gelation by creating an osmotic pressure gradient across the polymeric membrane that, through expansion, allows the passage of calcium ions. The effects of calcium concentration on the core gelation are explored.

Maceiczyk, R. M.; Lignos, I. G.; deMello, A. J. Online detection and automation methods in microfluidic nanomaterial synthesis. Current Opinion in Chemical Engineering 2015, 8, 29–35

Microfluidic reactors are increasingly being recognized as a promising tool for the synthesis of bespoke and high quality nanomaterials. Herein, we discuss currently available methods for interfacing microfluidic reactors with online analysis systems such as photothermal, fluorescence, absorbance, X-ray, backscattering and correlation spectroscopies. Integration of appropriate on-line detection methods enables the facile extraction of information relating to size, shape and chemical composition of the formed nanoparticles, thus greatly enhancing control over the synthetic process. Furthermore, we discuss recent approaches aimed at implementing ‘intelligent’ algorithms that use such extracted information for optimization and parameter space evaluation. Lastly, we provide brief opinion about future directions of this emerging field.

2014

Robert C. R. Wootton, Katherine Elvira and Andrew J. deMello. A simple theoretical basis for droplet induced surface fatigue. MicroTAS 2014, the 18th International Conference on Miniaturized Systems for Chemistry and Life Sciences, San Antonio, USA, pp. 1196–1198.

Surface wetting is a major source of droplet failure and contamination. We propose a simple theoretical treatment to model the effect of droplet wear on surface surfactant coverage, itself a major cause of surface degradation in use. The model showed good concordance with effects predicted by a numerical iterative treatment in MatLab Simbiology.

Ding, Y.; Casadevall i Solvas, X.; deMello, A. The “V-junction”: a novel structure for high-speed generation of bespoke droplet flows. The Analyst 2015, 140, 414–421

We present the use of microfluidic “V-junctions” as a droplet generation strategy that incorporates enhanced performance characteristics when compared to more traditional “T-junction” formats. This includes the ability to generate target-sized droplets from the very first one, efficient switching between multiple input samples, the production of a wide range of droplet sizes (and size gradients) and the facile generation of droplets with residence time gradients. Additionally, the use of V-junction droplet generators enables the suspension and subsequent resumption of droplet flows at times defined by the user. The high degree of operational flexibility allows a wide range of droplet sizes, payloads, spacings and generation frequencies to be obtained, which in turn provides for an enhanced design space for droplet-based experimentation. We show that the V-junction retains the simplicity of operation associated with T-junction formats, whilst offering functionalities normally associated with droplet-on-demand technologies.
» Analyst 2015 Cover

Robinson, T.; Valluri, P.; Kennedy, G.; Sardini, A.; Dunsby, C.; Neil, M. A. A.; Baldwin, G. S.; French, P. M. W.; de Mello, A. J. Analysis of DNA binding and nucleotide flipping kinetics using two-color two-photon fluorescence lifetime imaging microscopy. Analytical Chemistry 2014, 86, 10732–10740

Uracil DNA glycosylase plays a key role in DNA maintenance via base excision repair. Its role is to bind to DNA, locate unwanted uracil, and remove it using a base flipping mechanism. To date, kinetic analysis of this complex process has been achieved using stopped-flow analysis but, due to limitations in instrumental dead-times, discrimination of the “binding” and “base flipping” steps is compromised. Herein we present a novel approach for analyzing base flipping using a microfluidic mixer and two-color two-photon (2c2p) fluorescence lifetime imaging microscopy (FLIM). We demonstrate that 2c2p FLIM can simultaneously monitor binding and base flipping kinetics within the continuous flow microfluidic mixer, with results showing good agreement with computational fluid dynamics simulations.

Martino, C.; Berger, S.; Wootton, R. C. R.; deMello, A. J. A 3D-Printed Microcapillary Assembly for Facile Double Emulsion Generation. Lab on a Chip 2014, 14, 4178–4182

The design, fabrication and testing of facile microcapillary device assembly, suitable for monodisperse double emulsion production is reported. The interface is fabricated in a direct and rapid manner via 3D printing and shown to be robust in the controllable generation of both single and double emulsions at high generation frequencies.

Stanley, C. E.; Stöckli, M.; van Swaay, D.; Sabotič, J.; Kallio, P. T.; Künzler, M.; deMello, A. J.; Aebi, M. Probing bacterial-fungal interactions at the single cell level. Integrative Biology, 2014, 6, 935–945

Interactions between fungi and prokaryotes are abundant in many ecological systems. A wide variety of biomolecules regulate such interactions and many of them have found medicinal or biotechnological applications. However, studying a fungal-bacterial system at a cellular level is technically challenging. New microfluidic devices provided a platform for microscopic studies and for long-term, time-lapse experiments. Application of these novel tools revealed insights into in the dynamic interactions between the basidiomycete Coprinopsis cinerea and Bacillus subtilis. Direct contact was mediated by polar attachment of bacteria to only a subset of fungal hyphae suggesting a differential competence of fungal hyphae and thus differentiation of hyphae within a mycelium. The fungicidal activity of Bacillus subtilis was monitored at a cellular level and showed a novel mode of action on fungal hyphae.

Maceiczyk, R. M.; deMello, A. J. Fast and Reliable Metamodeling of Complex Reaction Spaces Using Universal Kriging. The Journal of Physical Chemistry C 2014, 118, 20026–20033

We report the application of metamodeling algorithms based on Universal Kriging for the controlled synthesis of compound semiconductor nanoparticles. Application of such a metamodel allows the prediction of reaction outcomes at arbitrary points within sparsely sampled parameter spaces as a function of reaction conditions. To demonstrate the applicability of Universal Kriging to chemical reaction screening within microfluidic reaction systems CdSe and CdSeTe quantum dots were synthesized by using a segmented flow capillary reactor. Variation of input reagent flows (to control reagent concentrations and reaction residence times) and online spectroscopic monitoring of product characteristics was achieved in a fully automated manner. The resulting fluorescence spectra are analyzed to extract the fwhm, wavelength maximum, and intensity of the band-edge emission. These values are subsequently used as inputs for the Universal Kriging metamodeling algorithm to predict the reactor output at arbitrary points within accessible parameter space. Results demonstrate that the algorithm can predict reaction outcomes with high accuracy and reliability.

Phillips, T. W.; Lignos, I. G.; Maceiczyk, R. M.; deMello, A. J.; deMello, J. C. Nanocrystal synthesis in microfluidic reactors: where next?. Lab on a Chip 2014, 14, 3172-3180

The past decade has seen a steady rise in the use of microfluidic reactors for nanocrystal synthesis, with numerous studies reporting improved reaction control relative to conventional batch chemistry. However, flow synthesis procedures continue to lag behind batch methods in terms of chemical sophistication and the range of accessible materials, with most reports having involved simple one- or two-step chemical procedures directly adapted from proven batch protocols. Here we examine the current status of microscale methods for nanocrystal synthesis, and consider what role microreactors might ultimately play in laboratory-scale research and industrial production.

Choi, J.-W.; Lee, S.; Lee, D.-H.; Kim, J.; deMello, A. J.; Chang, S.-I. Integrated pneumatic micro-pumps for high-throughput droplet-based microfluidics. RSC Advance, 2014, 4, 20341–20345

Droplet-based microfluidic systems have recently emerged as powerful experimental tools in the chemical and biological sciences. In conventional droplet-based microfluidics, controlled droplet generation is normally achieved using precision syringe pumps, where the sample is delivered to the microdevice using external tubing that possesses an appreciable dead volume. Accordingly, there is an unmet need for a droplet generation system that does not require the use of syringe pumps. Herein, we report the integration of pneumatic micro-pumps with droplet-based microfluidic systems and their subsequent use in high-throughput biological experimentation. The efficacy of the system is demonstrated by investigating the interaction and the binding inhibition between angiogenin and the anti-angiogenin antibody with a dissociation constant (KD) value of 9.1 ± 3.5 nM and a half maximal inhibitory concentration (IC50) value of 12.2 ± 2.5 nM, respectively.

Lignos, I.; Protesescu, L.; Stavrakis, S.; Piveteau, L.; Speirs, M. J.; Loi, M. A.; Kovalenko, M. V.; deMello, A. J. Facile Droplet-based Microfluidic Synthesis of Monodisperse IV–VI Semiconductor Nanocrystals with Coupled In-Line NIR Fluorescence Detection. Chemistry of Materials 2014, 26, 2975–2982

We describe the realization of a droplet-based microfluidic platform for the controlled and reproducible synthesis of lead chalcogenide (PbS, PbSe) nanocrystal quantum dots (QDs). Monodisperse nanocrystals were synthesized over a wide range of experimental conditions, with real-time assessment and fine-tuning of material properties being achieved using NIR fluorescence spectroscopy. Importantly, we show for the first time that real-time monitoring of the synthetic process allows for rapid optimization of reaction conditions and the synthesis of high quality PbS nanocrystals, emitting in the range of 765–1600 nm, without any post-synthetic processing. The segmented-flow capillary reactor exhibits stable droplet generation and reproducible synthesis of PbS nanocrystals with high photoluminescence quantum yields (28%) over extended periods of time (3–6 h). Furthermore, the produced NIR-emitting nanoparticles were successfully used in the fabrication of Schottky solar cells, exhibiting a power conversion efficiency of 3.4% under simulated AM 1.5 illumination. Finally, the droplet-based microfluidic platform was used to synthesize PbSe nanocrystals having photoluminescence peaks in the range of 860–1600 nm, showing the exceptional control and stability of the reactor.

Kim, J.; Chang, S.-I.; deMello, A. J.; O’Hare, D. Integration of monolithic porous polymer with droplet-based microfluidics on a chip for nano picoliter volume sample analysis. Nano Convergence 2014, 1

In this paper, a porous polymer nanostructure has been integrated with droplet-based microfluidics in a single planar format. Monolithic porous polymer (MPP) was formed selectively within a microfluidic channel. The resulting analyte bands were sequentially comartmentalised into droplets. This device reduces band broadening and the effects of post-column dead volume by the combination of the two techniques. Moreover it offers the precise control of nano/picoliter volume samples.

Berger, S.; Stawikowska, J.; van Swaay, D.; deMello, A. Continuous Suspension of Lipids in Oil by the Selective Removal of Chloroform via Microfluidic Membrane Separation. Industrial & Engineering Chemistry Research 2014, 53, 9256–9261

A continuous flow method for the suspension of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) lipids in oil using a microfluidic platform is presented. The system consists of a microfluidic device housing a semipermeable membrane, a vacuum pump, and a syringe pump. Separation is achieved using a counter current flow of chloroform and a lipid containing oil stream, driven by the syringe pump and vacuum. Using such a system, a high efficiency extraction method was realized through the use of a semipermeable polydimethylsiloxane (PDMS) membrane on an anodized aluminum oxide (AAO) support. For a liquid flow rate of 5 μL/min, an air flow rate of 100 mL/min, and initial chloroform concentrations between 0.245 and 1.619 M, extraction rates of 93.5% to 97.9% and a retentate stream purity of between 99.79% and 99.29% were achieved.

Zhao, Y.; Pereira, F.; deMello, A. J.; Morgan, H.; Niu, X. Droplet-based in situ compartmentalization of chemically separated components after isoelectric focusing in a Slipchip. Lab on a Chip 2014, 14, 555–561

Isoelectric focusing (IEF) is a powerful and widely used technique for protein separation and purification. There are many embodiments of microscale IEF that use capillary or microfluidic chips for the analysis of small sample volumes. Nevertheless, collecting the separated sample volumes without causing remixing remains a challenge. Herein, we describe a microfluidic Slipchip device that is able to efficiently compartmentalize focused analyte bands in situ into microdroplets. The device contains a microfluidic “zig-zag” separation channel that is composed of a sequence of wells formed in the two halves of the Slipchip. The analytes are focused in the channel and then compartmentalised into droplets by slipping the chip. Importantly, sample droplets can be analysed on chip or collected for subsequent analysis using electrophoresis or mass spectrometry for example. To demonstrate this approach, we perform IEF separation using standard markers and protein samples, with on-chip post-processing. Compared to alternative approaches for sample collection, the method avoids remixing, is scalable and is easily hyphenated with the other analytical methods.

Gong, X.; Patil, A. V.; Ivanov, A. P.; Kong, Q.; Gibb, T.; Dogan, F.; deMello, A. J.; Edel, J. B. Label-Free In-Flow Detection of Single DNA Molecules using Glass Nanopipettes. Analytical Chemistry 2014, 86, 835–841

With the view of enhancing the functionality of label-free single molecule nanopore-based detection, we have designed and developed a highly robust, mechanically stable, integrated nanopipette-microfluidic device which combines the recognized advantages of microfluidic systems and the unique properties/advantages of nanopipettes. Unlike more typical planar solid-state nanopores, which have inherent geometrical constraints, nanopipettes can be easily positioned at any point within a microfluidic channel. This is highly advantageous, especially when taking into account fluid flow properties. We show that we are able to detect and discriminate between DNA molecules of varying lengths when motivated through a microfluidic channel, upon the application of appropriate voltage bias across the nanopipette. The effects of applied voltage and volumetric flow rates have been studied to ascertain translocation event frequency and capture rate. Additionally, by exploiting the advantages associated with microfluidic systems (such as flow control and concomitant control over analyte concentration/presence), we show that the technology offers a new opportunity for single molecule detection and recognition in microfluidic devices.

Dressler, O. J.; Maceiczyk, R. M.; Chang, S.-I.; deMello, A. J. Droplet-Based Microfluidics: Enabling Impact on Drug Discovery. Journal of Biomolecular Screening 2014, 19, 483–496

Over the past two decades, the application of microengineered systems in the chemical and biological sciences has transformed the way in which high-throughput experimentation is performed. The ability to fabricate complex microfluidic architectures has allowed scientists to create new experimental formats for processing ultra-small analytical volumes in short periods and with high efficiency. The development of such microfluidic systems has been driven by a range of fundamental features that accompany miniaturization. These include the ability to handle small sample volumes, ultra-low fabrication costs, reduced analysis times, enhanced operational flexibility, facile automation, and the ability to integrate functional components within complex analytical schemes. Herein we discuss the impact of microfluidics in the area of high-throughput screening and drug discovery and highlight some of the most pertinent studies in the recent literature.

L.D. van Vliet , F. Gielen , A. Sinha , B.T. Koprowski , J.B. Edel , X. Niu , A.J. deMello. Droplet-on-Demand Platform For Biochemical Screening and Drug Discovery. Micro Total Analysis Systems 2014

We present new biochemical applications for an automated droplet screening system (the Mitos Dropix). This droplet-on-demand robotic platform was previously shown to perform automated dilution gradients that can be detected by absorbance or fluorescence in a time-resolved fashion without the need for a chip. We now present reproducibility data for the Dropix and show that it can be integrated with microfluidic devices to merge and split specific sequences of droplets. It can also be used to encapsulate cells and multi-cellular organisms.

O.J. Dressler, T. Yang, S. Chang, R.C.R. Wootton, A.J. deMello. Investigating Inter-Droplet Mass Transfer in Flow Utilizing High Accuracy Synchronization. Micro Total Analysis Systems 2014

We report a microfluidic system for the measurement of mass transfer between microfluidic droplets in flow. A high-accuracy droplet synchronization structure allows for the passive ordering of two droplet types which enabled quantification of both osmotic and diffusive transfer between droplets.

2013

van Swaay, D.; Mächler, J.-P.; Stanley, C.; deMello, A. A chip-to-world connector with a built-in reservoir for simple small-volume sample injection. Lab on a Chip 2014, 14, 178–181

We present a novel connector that allows for easy handling and injection of sample volumes between 1 and 20 μl. All tubing connections between external pumps and the microfluidic device are established before the sample is introduced into a sealable reservoir built into the connector. This approach allows for multiple injections of small sample volumes without the need to dismantle the chip-tubing assembly. We demonstrate that the connector reservoir seal can withstand pressures of up to 6 bar, that opening or closing the reservoir does not dislocate the sample by more than 35 nl, and that the connector can be used for injecting samples into both miscible and immiscible carrier fluids.

Anandkumar Rane, Xavier Casadevall i Solvas and Andrew deMello. Particle Ordering Using Dean Force-Based Inertial Microfluidics. MicroTAS 2013, the 17th International Conference on Miniaturized Systems for Chemistry and Life Sciences, Freiburg, Germany, p735.

Herein, we have studied the effect of channel width, particle size and concentration on particle ordering in Dean force-based devices. We observed that once the particles are focused to their equilibrium position in the channel, they tend to order at an equilibrium inter-particle distance (β). β is independent of width of the device and particle concentra-tion, and is observed to be 18-22 μm for 10 μm and 12 μm particles.

Yun Ding, Stavros Stavrakis, Xevier Casadevall i Solvas, and Andrew J. deMello. A High Throughput Droplet-Based Microfluidic Barcode Generator. MicroTAS 2013, the 17th International Conference on Miniaturized Systems for Chemistry and Life Sciences, Freiburg, Germany, p299.

The labelling (or barcoding) of microdroplets so that each unit can individually be identified and monitored is an important missing link for the application of droplet-based microfluidic platforms in high throughput chemical and biological assays. We present an efficient droplet barcode generator based on a simple T-junction design modified with four aqueous phase inlets. Codes are generated by combining two fluorophores at different concentrations, which is achieved by dynamically adjusting the ratio of the four aqueous flow-rates (two dyes, two buffers) using programmable syringe pumps. In a proof-of-concept experiment over 500 distinguishable codes were generated in less than 20 seconds.

Ioannis Lignos, Katherine S. Elvira, Robert C. R. Wootton and Andrew J. deMello. Gas-liquid microfluidic reactors for the oxidative homocoupling of phenylacetylene. MicroTAS 2013, the 17th International Conference on Miniaturized Systems for Chemistry and Life Sciences, Freiburg, Germany, pp. 593–595.

We report a new approach for performing oxidative homocoupling reactions. Specifically, a gas-liquid microfluidic reactor was developed to carry out the Glaser-Hay reaction of phenylacetylene. A range of reaction conditions were sampled to find those that produced the highest yields of 1,4-diphenylbutadiyne. Product yields of up to 100% were attained in very short residence times (7-30 min) and under standard experimental conditions when compared to conventional synthetic methods. These studies represent the first multiphase microfluidic method for the synthesis of diynes.

Elvira, K. S.; i Solvas, X. C.; Wootton, R. C. R.; deMello, A. J. The past, present and potential for microfluidic reactor technology in chemical synthesis. Nature Chemistry 2013, 5, 905–915

The past two decades have seen far-reaching progress in the development of microfluidic systems for use in the chemical and biological sciences. Here we assess the utility of microfluidic reactor technology as a tool in chemical synthesis in both academic research and industrial applications. We highlight the successes and failures of past research in the field and provide a catalogue of chemistries performed in a microfluidic reactor. We then assess the current roadblocks hindering the widespread use of microfluidic reactors from the perspectives of both synthetic chemistry and industrial application. Finally, we set out seven challenges that we hope will inspire future research in this field.

Niu, X.; Pereira, F.; Edel, J. B.; de Mello, A. J. Droplet-Interfaced Microchip and Capillary Electrophoretic Separations. Analytical Chemistry 2013, 85, 8654–8660

Both capillary and chip-based electrophoresis are powerful separation methods widely used for the separation of complex analytical mixtures in the fields of genomics, proteomics, metabolomics, and cellular analysis. However their utility as basic tools in high-throughput analysis and multidimensional separations has been hampered by inefficient or biased sample injection methods. Herein, we address this problem through the development of a simple separation platform that incorporates droplet-based microfluidic module for the encapsulation of analytes prior to the analytical separation. This method allows for the precise and reproducible injection of pL to nL volume isolated plugs into an electrophoretic separation channel. The developed platform is free from inter sample contamination, allows for small sample size, high-throughput analysis, and can provide quantitative analytical information.

Cho, S.; Kang, D.-K.; Sim, S.; Geier, F.; Kim, J.-Y.; Niu, X.; Edel, J. B.; Chang, S.-I.; Wootton, R. C. R.; Elvira, K. S.; deMello, A. J. Droplet-based microfluidic platform for high-throughput, multi-parameter screening of photosensitizer activity. Analytical Chemistry 2013, 85, 8866–8872

We present a fully integrated droplet-based microfluidic platform for the high-throughput assessment of photodynamic therapy photosensitizer (PDT) efficacy on Escherichia coli. The described platform is able to controllably encapsulate cells and photosensitizer within pL-volume droplets, incubate the droplets over the course of several days, add predetermined concentrations of viability assay agents, expose droplets to varying doses of electromagnetic radiation, and detect both live and dead cells online to score cell viability. The viability of cells after encapsulation and incubation is assessed in a direct fashion, and the viability scoring method is compared to model live/dead systems for calibration. Final results are validated against conventional colony forming unit assays. In addition, we show that the platform can be used to perform concurrent measurements of light and dark toxicity of the PDT agents and that the platform allows simultaneous measurement of experimental parameters that include dark toxicity, photosensitizer concentration, light dose, and oxygenation levels for the development and testing of PDT agents.

Pereira, F.; Niu, X.; deMello, A. J. A Nano LC-MALDI Mass Spectrometry Droplet Interface for the Analysis of Complex Protein Samples. PLoS ONE 2013, 8, e63087

The integration of matrix-assisted laser desorption ionization (MALDI) mass spectrometry with an upstream analytical separations (such as liquid chromatography and electrophoresis) has opened up new opportunities for the automated investigation of complex protein and peptide mixtures. The ability to efficiently analyze complex proteomic mixtures in this manner is primarily determined by the ability to preserve spatial discrimination of sample components as they leave the separation column. Current interfacing methods are problematic in this respect since minimum fraction volumes are limited to several microliters. Herein we show for the first time an LC-MALDI interface based on the formation, processing and destruction of a segmented flow. The interface consists of a droplet-generator to fractionate LC effluent into nL-volume droplets and a deposition probe that transfers the sample (and MALDI matrix) onto a conventional MALDI-MS target. The efficacy of the method is demonstrated through the analysis of Trypsin digests of both BSA and Cytochrome C, with a 50% enhancement in analytical performance when compared to conventional interface technology.

Gielen, F.; van Vliet, L.; Koprowski, B. T.; Devenish, S. R. A.; Fischlechner, M.; Edel, J. B.; Niu, X.; deMello, A. J.; Hollfelder, F. A Fully Unsupervised Compartment-on-demand Platform for Precise Nanolitre Assays of Time-Dependent Steady-State Enzyme Kinetics and Inhibition. Analytical Chemistry 2013, 85, 4761–4769

The ability to miniaturize biochemical assays in water-in-oil emulsion droplets allows a massive scale-down of reaction volumes, so that high-throughput experimentation can be performed more economically and more efficiently. Generating such droplets in compartment-on-demand (COD) platforms is the basis for rapid, automated screening of chemical and biological libraries with minimal volume consumption. Herein, we describe the implementation of such a COD platform to perform high precision nanoliter assays. The coupling of a COD platform to a droplet absorbance detection system results in a fully automated analytical platform. Michaelis-Menten parameters of 4-nitrophenyl glucopyranoside hydrolysis by sweet almond β-glucosidase can be generated based on 24 time courses taken at different substrate concentrations with a total volume consumption of only 1.4 µL. Importantly, kinetic parameters can be derived in a fully unsupervised manner within 20 minutes; droplet production (5 minutes), initial reading of the droplet sequence (5 minutes), droplet fusion to initiate the reaction and read-out over time (10 minutes). Similarly the inhibition of the enzymatic reaction by conduritol B epoxide and 1-deoxynojirimycin was measured and Ki values were determined. In both cases the kinetic parameters obtained in droplets were identical within error to values obtained in titer plates, despite by >104-fold volume reduction, from micro- to nanoliters.

van Swaay, D.; deMello, A. Microfluidic methods for forming liposomes. Lab on a Chip 2013, 13, 752

Liposome structures have a wide range of applications in biology, biochemistry, and biophysics. As a result, several methods for forming liposomes have been developed. This review provides a critical comparison of existing microfluidic technologies for forming liposomes and, when applicable, a comparison with their analogous macroscale counterparts. The properties of the generated liposomes, including size, size distribution, lamellarity, membrane composition, and encapsulation efficiency, form the basis for comparison. We hope that this critique will allow the reader to make an informed decision as to which method should be used for a given biological application.

Elvira, K. S.; Wootton, R. C. R.; Reis, N. M.; Mackley, M. R.; deMello, A. J. Through-wall mass transport as a modality for safe generation of singlet oxygen in continuous flows. ACS Sustainable Chemistry & Engineering 2013, 1, 209–213

Singlet oxygen, a reactive oxygen species, has been a basic synthetic tool in the laboratory for many years. It can be generated either through a chemical process or most commonly via a photochemical process mediated by a sensitizing dye. The relative paucity of singlet oxygen employment in fine chemical industrial settings can be attributed to many factors, not least the requirement for excessive quantities of oxygenated organic solvents and the dangers that these represent. Microcapillary films (MCFs) are comprised of multiple parallel channels embedded in a plastic film. In this study, MCFs are employed as flow reactor systems for the singlet oxygen mediated synthesis of ascaridole. No gaseous oxygen is supplied directly to the reaction, rather mass transport occurs exclusively through the reactor walls. The rate of production of ascaridole was found to be strongly dependent on the partial pressure of oxygen present within the reaction system. This methodology significantly simplifies reactor design, allows for increased safety of operation, and provides for space–time yields over 20 times larger than the corresponding bulk synthesis.

Yan Zhao, Fiona Pereira, Andrew de Mello, Hywel Morgan, Xize Niu. Droplet-Based Compartmentalization After Isoelectric Focusing in a Slipchip. Micro Total Analysis Systems 2013

Isoelectric focusing (IEF) is a widely used technique for protein separation. We describe a novel Slipchip device that allows ‘in situ’ compartmentalization of separated analytes into droplets after IEF in microfluidic channel. The device prevents remixing of separated components and provides facile hyphenations for subsequent analysis. The droplets can be analyzed either on chip or collected for off line analysis, such as electrophoresis or mass spectrometry. We demonstrate IEF separation using standard markers and proteins, with on chip pH calibration. Compared with other approaches of sample collections, this method is diffusion free, scalable and can be easily hyphenated with the other analytical methods.

2012

Yamazaki, M.; Krishnadasan, S.; deMello, A. J.; deMello, J. C. Non-emissive plastic colour filters for fluorescence detection. Lab on a Chip 2012, 12, 4313–4320

We report the fabrication of non-emissive short- and long-pass filters on plastic for high sensitivity fluorescence detection. The filters were prepared by overnight immersion of titania-coated polyethylene terephthalate (PET) in an appropriate dye solution – xylene cyanol for short-pass filtering and fluorescein disodium salt for long-pass filtering – followed by repeated washing to remove excess dye. The interface between the titania and the dye molecule induces efficient quenching of photo-generated excitons in the dye molecule, reducing auto-fluorescence to negligible values and so overcoming the principal weakness of conventional colour filters. Using the filters in conjunction with a 505 nm cyan light-emitting diode and a Si photodiode, dose-response measurements were made for T8661 Transfluosphere beads in the concentration range 1 × 10^9 to 1 × 10^5 beads μL−1, yielding a limit of detection of 3 × 10^4 beads μL−1. The LED/short-pass filter/T8661/long-pass filter/Si-photodiode combination reported here offers an attractive solution for sensitive, low cost fluorescence detection that is readily applicable to a wide range of bead-based immunodiagnostic assays.

Niu, X.; deMello, A. J. Building droplet-based microfluidic systems for biological analysis. Biochemical Society Transactions 2012, 40, 615–623

In the present paper, we review and discuss current developments and challenges in the field of droplet-based microfluidics. This discussion includes an assessment of the basic fluid dynamics of segmented flows, material requirements, fundamental unit operations and how integration of functional components can be applied to specific biological problems.

Kim, J.-Y.; Cho, S.-W.; Kang, D.-K.; Edel, J. B.; Chang, S.-I.; deMello, A. J.; O’Hare, D. Lab-chip HPLC with integrated droplet-based microfluidics for separation and high frequency compartmentalisation. Chemical Communications 2012, 48, 9144–9146

We demonstrate the integration of a droplet-based microfluidic device with high performance liquid chromatography (HPLC) in a monolithic format. Sequential operations of separation, compartmentalisation and concentration counter were conducted on a monolithic chip. This describes the use of droplet-based microfluidics for the preservation of chromatographic separa- tions, and its potential application as a high frequency fraction collector.

Elani, Y.; deMello, A. J.; Niu, X.; Ces, O. Novel technologies for the formation of 2-D and 3-D droplet interface bilayer networks. Lab on a Chip 2012, 12, 3514–3520

Droplet interface bilayer (DIB) networks have vast potential in the field of membrane biophysics, synthetic biology, and functional bio-electronics. However a technological bottleneck exists in network fabrication: existing methods are limited in terms of their automation, throughput, versatility, and ability to form well-defined 3-D networks. We have developed a series of novel and low-cost methodologies which address these limitations. The first involves building DIB networks around the contours of a microfluidic chip. The second uses flow rate and droplet size control to influence droplet packing geometries within a microfluidic chamber. The latter method enables the controlled formation of various 3-D network arrays consisting of thousands of interconnected symmetric and asymmetric lipid bilayers for the first time. Both approaches allow individual droplet position and composition to be controlled, paving the way for complex on-chip functional network synthesis.

Goyder, M. S.; Willison, K. R.; Klug, D. R.; DeMello, A. J.; Ces, O. Affinity chromatography and capillary electrophoresis for analysis of the yeast ribosomal proteins. BMB Reports 2012, 45, 233–238

We present a top down separation platform for yeast ribosomal proteins using affinity chromatography and capillary electro- phoresis which is designed to allow deposition of proteins onto a substrate. FLAG tagged ribosomes were affinity purified, and rRNA acid precipitation was performed on the ribosomes fol- lowed by capillary electrophoresis to separate the ribosomal proteins. Over 26 peaks were detected with excellent reprodu- cibility (<0.5% RSD migration time). This is the first reported separation of eukaryotic ribosomal proteins using capillary electrophoresis. The two stages in this workflow, affinity chro- matography and capillary electrophoresis, share the advantages that they are fast, flexible and have small sample requirements in comparison to more commonly used techniques. This meth- od is a remarkably quick route from cell to separation that has the potential to be coupled to high throughput readout plat- forms for studies of the ribosomal proteome.

Yashina, A.; Meldrum, F.; deMello, A. Calcium carbonate polymorph control using droplet-based microfluidics. Biomicrofluidics 2012, 6, 022001

Calcium carbonate (CaCO3) is one of the most abundant minerals and of high importance in many areas of science including global CO2 exchange, industrial water treatment energy storage, and the formation of shells and skeletons. Industrially, calcium carbonate is also used in the production of cement, glasses, paints, plastics, rubbers, ceramics, and steel, as well as being a key material in oil refining and iron ore purification. CaCO3 displays a complex polymorphic behaviour which, despite numerous experiments, remains poorly characterised. In this paper, we report the use of a segmented-flow microfluidic reactor for the controlled precipitation of calcium carbonate and compare the resulting crystal properties with those obtained using both continuous flow microfluidic reactors and conventional bulk methods. Through combination of equal volumes of equimolar aqueous solutions of calcium chloride and sodium carbonate on the picoliter scale, it was possible to achieve excellent definition of both crystal size and size distribution. Furthermore, highly reproducible control over crystal polymorph could be realised, such that pure calcite, pure vaterite, or a mixture of calcite and vaterite could be precipitated depending on the reaction conditions and droplet-volumes employed. In contrast, the crystals precipitated in the continuous flow and bulk systems comprised of a mixture of calcite and vaterite and exhibited a broad distribution of sizes for all reaction conditions investigated.

Elvira, K. S.; Leatherbarrow, R.; Edel, J.; deMello, A. Droplet dispensing in digital microfluidic devices: Assessment of long-term reproducibility. Biomicrofluidics 2012, 6, 022003

We report an in-depth study of the long-term reproducibility and reliability of droplet dispensing in digital microfluidic devices (DMF). This involved dispensing droplets from a reservoir, measuring the volume of both the droplet and the reservoir droplet and then returning the daughter droplet to the original reservoir. The repetition of this process over the course of several hundred iterations offers, for the first time, a long-term view of droplet dispensing in DMF devices. Results indicate that the ratio between the spacer thickness and the electrode size influences the reliability of droplet dispensing. In addition, when the separation between the plates is large, the volume of the reservoir greatly affects the reproducibility in the volume of the dispensed droplets, creating “reliability regimes.” We conclude that droplet dispensing exhibits superior reliability as inter-plate device spacing is decreased, and the daughter droplet volume is most consistent when the reservoir volume matches that of the reservoir electrode.

Choi, J.-W.; Kang, D.-K.; Park, H.; deMello, A. J.; Chang, S.-I. High-Throughput Analysis of Protein–Protein Interactions in Picoliter-Volume Droplets Using Fluorescence Polarization. Analytical Chemistry 2012, 84, 3849–3854

Droplet-based microfluidic systems have emerged as a powerful platform for performing high-throughput biological experimentation. In addition, fluorescence polarization has been shown to be effective in reporting a diversity of bimolecular events such as protein–protein, DNA–protein, DNA–DNA, receptor–ligand, enzyme–substrate, and protein–drug interactions. Herein, we report the use of fluorescence polarization for high-throughput protein–protein interaction analysis in a droplet-based microfluidic system. To demonstrate the efficacy of the approach, we investigate the interaction between angiogenin (ANG) and antiangiogenin antibody (anti-ANG Ab) and demonstrate the efficient extraction of dissociation constants (KD = 10.4 ± 3.3 nM) within short time periods.

Stanley, C. E.; Wootton, R. C. R.; deMello, A. J. Continuous and segmented flow microfluidics: Applications in high-throughput chemistry and biology. CHIMIA International Journal for Chemistry 2012, 66, 88–98

This account highlights some of our recent activities focused on developing microfluidic technologies for application in high-throughput and high-information content chemical and biological analysis. Specifically, we discuss the use of continuous and segmented flow microfluidics for artificial membrane formation, the analysis of single cells and organisms, nanomaterial synthesis and DNA amplification via the polymerase chain reaction. In addition, we report on recent developments in small-volume detection technology that allow access to the vast amounts of chemical and biological information afforded by microfluidic systems.

Wootton, R. C. R.; deMello, A. J. Microfluidics: Analog-to-digital drug screening. Nature 2012, 483, 43–44

Current methods for screening libraries of compounds for biological activity are rather cumbersome, slow and imprecise. A method that breaks up a continuous flow of a compound\\\'s solution into droplets offers radical improvements.

Gong, X.; Miller, P. W.; Gee, A. D.; Long, N. J.; de Mello, A. J.; Vilar, R. Gas–Liquid Segmented Flow Microfluidics for Screening Pd-Catalyzed Carbonylation Reactions. Chemistry - A European Journal 2012, 18, 2768–2772

Go with the (segmented) flow: A gas–liquid microfluidic reactor system has been developed to study Pd-catalyzed carbonylation reactions over a range of flow regimes and reaction conditions (see picture). The segmented gas–liquid flow regime, in comparison to annular flow, enables reactions to be studied over longer reaction times and without the buildup of unwanted Pd particles.

Kumar, K.; Nightingale, A. M.; Krishnadasan, S. H.; Kamaly, N.; Wylenzinska-Arridge, M.; Zeissler, K.; Branford, W. R.; Ware, E.; deMello, A. J.; deMello, J. C. Direct synthesis of dextran-coated superparamagnetic iron oxide nanoparticles in a capillary-based droplet reactor. Journal of Materials Chemistry 2012, 22, 4704–4708

We describe the controlled synthesis of dextran-coated superparamagnetic iron oxide nanoparticles (SPIONs) using a stable passively-driven capillary-based droplet reactor. High quality highly crystalline particles were obtained with a narrow size distribution of mean diameter 3.6 nm and standard deviation 0.8 nm. The particles were evaluated for use in MRI, and found to exhibit a large saturation magnetisation of 58 emu/g and a high T2 relaxivity of 66 mM−1s−1 at 4.7 T, signifying good MRI contrast enhancement properties.

Soongwon Cho, Dong-Ku Kang, Steven Sim, Florian Geier, Florian Geier, Jin-Young Kim, Soo-Ik Chang, Joshua Edel, Robert Wootton, Andrew deMello. A Droplet-Based Microfluidic System for Highthroughput Screening of Photosensitisers Against Microbial Organisms. Micro Total Analysis Systems 2012

Herein, we present a modular droplet-based microfluidic approach for performing high throughput cytotoxicity screening of photosensitizers against microbial organisms. Multiple novel fluidic operation modalities such as large-scale chamber based light irradiation, reinjection and low voltage driven electrocoalescence are introduced. Also, photosensitiser drug cytotoxicity on E.coli cells are evaluated in microfluidic device using fluorescent viability assay indicator and compared with conventional colony forming unit counting cytotoxicity assay.

Jae-Won Choi, Dong-Ku Kan, Hyun Park, Andrew J. deMello. High-throughput Analysis of Protein-Protein Interactions In Droplet-Based Microfluidics Using Fluorescence Polarization. Micro Total Analysis Systems 2012

In recent years droplet-based (or segmented-flow) microfluidic systems have emerged as a powerful technological platform for performing high-throughput chemical and biological experimentation. Herein, we have demonstrated the combination of fluorescence polarization and droplet-based microfluidics for the rapid analysis of protein-protein interactions. Fluorescence polarization is powerful technique for analysis of biomolecular interaction since it is truly homogenous assay format. In this study, specifically, the interaction between angiogenin and anti-angiogenin antibody was successfully analyzed in short times of 40 hertz and with high precision. Angiogenin is a small polypeptide implicated in angiogenesis and in tumor growth.

Gielen, F.; deMello, A. J.; Edel, J. B. Dielectric Cell Response in Highly Conductive Buffers. Analytical Chemistry 2012, 84, 1849–1853

We present a novel method for the identification of live and dead T-cells, dynamically flowing within highly conductive buffers. This technique discriminates between live and dead (heat treated) cells on the basis of dielectric properties variations. The key advantage of this technique lies in its operational simplicity, since cells do not have to be resuspended in isotonic low conductivity media. Herein, we demonstrate that at 40 MHz, we are able to statistically distinguish between live and dead cell populations.

2011

Cho, S.-W.; Kang, D.-K.; Choo, J.-B.; Demllo, A. J.; Chang, S.-I. Recent advances in microfluidic technologies for biochemistry and molecular biology. BMB Reports 2011, 44, 705–712

Advances in the fields of proteomics and genomics have necessitated the development of high-throughput screening methods (HTS) for the systematic transformation of large amounts of biological chemical data into an organized database of knowledge. Microfluidic systems are ideally suited for high-throughput biochemical experimentation since they offer high analytical throughput, consume minute quantities of expensive biological reagents, exhibit superior sensitivity and functionality compared to traditional micro-array techniques and can be integrated within complex experimental work flows. A range of basic biochemical and molecular biological operations have been transferred to chip-based microfluidic formats over the last decade, including gene sequencing, emulsion PCR, immunoassays, electrophoresis, cell-based assays, expression cloning and macromolecule blotting. In this review, we highlight some of the recent advances in the application of microfluidics to biochemistry and molecular biology.

Casadevall i Solvas, X.; Niu, X.; Leeper, K.; Cho, S.; Chang, S.-I.; Edel, J. B.; deMello, A. J. Fluorescence detection methods for microfluidic droplet platforms. Journal of Visualized Experiments 2011

The development of microfluidic platforms for performing chemistry and biology has in large part been driven by a range of potential benefits that accompany system miniaturisation. Advantages include the ability to efficiently process nano- to femoto- liter volumes of sample, facile integration of functional components, an intrinsic predisposition towards large-scale multiplexing, enhanced analytical throughput, improved control and reduced instrumental footprints.1\\\\r\\\\nIn recent years much interest has focussed on the development of droplet-based (or segmented flow) microfluidic systems and their potential as platforms in high-throughput experimentation.2-4 Here water-in-oil emulsions are made to spontaneously form in microfluidic channels as a result of capillary instabilities between the two immiscible phases. Importantly, microdroplets of precisely defined volumes and compositions can be generated at frequencies of several kHz. Furthermore, by encapsulating reagents of interest within isolated compartments separated by a continuous immiscible phase, both sample cross-talk and dispersion (diffusion- and Taylor-based) can be eliminated, which leads to minimal cross-contamination and the ability to time analytical processes with great accuracy. Additionally, since there is no contact between the contents of the droplets and the channel walls (which are wetted by the continuous phase) absorption and loss of reagents on the channel walls is prevented.\\\\r\\\\nOnce droplets of this kind have been generated and processed, it is necessary to extract the required analytical information. In this respect the detection method of choice should be rapid, provide high-sensitivity and low limits of detection, be applicable to a range of molecular species, be non-destructive and be able to be integrated with microfluidic devices in a facile manner. To address this need we have developed a suite of experimental tools and protocols that enable the extraction of large amounts of photophysical information from small-volume environments, and are applicable to the analysis of a wide range of physical, chemical and biological parameters. Herein two examples of these methods are presented and applied to the detection of single cells and the mapping of mixing processes inside picoliter-volume droplets. We report the entire experimental process including microfluidic chip fabrication, the optical setup and the process of droplet generation and detection.

Fiona Pereira, Xize Niu, Petra S. Dittrich and Andrew J. deMello. Droplet-Based Sample Injection for Chip-Based Analytical Separations. Chromatography Today, 2011, 12-14.

The advent of capillary and chip-based electrophoresis has opened up new possibilities for high-throughput analysis of a diversity of biological systems. The high-resolution separations typical of chip-based electrophoresis are in large part defined by the ability to introduce small sample volumes into the separation channel. This is not a trivial process and standard electrokinetic and hydrodynamic methods are far from ideal. Herein, we review recent studies that integrate droplet-based and continuous flow microfluidics to provide an alternative injection mechanism that is simple to implement and enables reproducible transport of defined sample volumes without bias.

Kim, J.; deMello, A. J.; Chang, S.-I.; Hong, J.; O’Hare, D. Thermoset polyester droplet-based microfluidic devices for high frequency generation. Lab on a Chip 2011, 11, 4108–4112

The vast majority of droplet-based microfluidic devices are made from polydimethylsiloxane (PDMS). Unfortunately PDMS is not suitable for high frequency droplet generation at high operating pressure due to its low shear modulus. In this paper, we report the fabrication and testing of microfluidic devices using thermoset polyester (TPE). The optical characteristics of the fabricated devices were assessed and substrate resistance to pressure also investigated. TPE devices bonded using an O(2) plasma treated PET substrate at 76 °C were shown to function efficiently at pressures up to 18 MPa. TPE material retains many of the attractive features of PDMS such as ease of fabrication but significantly, has superior mechanical properties. The improved resistance of TPE to high pressures enabled investigation of high frequency droplet generation as a function of a wide range of flow-rates with three different oils as continuous phase.

Chansin, G. A. T.; Hong, J.; Dusting, J.; deMello, A. J.; Albrecht, T.; Edel, J. B. Resizing Metal-Coated Nanopores Using a Scanning Electron Microscope. Small 2011, 7, 2736–2741

Electron beam-induced shrinkage provides a convenient way of resizing solid-state nanopores in Si3N4 membranes. Here, a scanning electron microscope (SEM) has been used to resize a range of different focussed ion beam-milled nanopores in Al-coated Si3N4 membranes. Energy-dispersive X-ray spectra and SEM images acquired during resizing highlight that a time-variant carbon deposition process is the dominant mechanism of pore shrinkage, although granular structures on the membrane surface in the vicinity of the pores suggest that competing processes may occur. Shrinkage is observed on the Al side of the pore as well as on the Si3N4 side, while the shrinkage rate is observed to be dependent on a variety of factors.

Xavier Casadevall i Solvas, Florian M. Geier, Armand M. Leroi, Jake G. Bundy, Joshua B. Edel and Andrew J. deMello. High-throughput age synchronisation of Caenorhabditis elegans. Chemical Communications, 2011, 47, 9801–9803.

We present a passive microfluidic strategy for sorting adult\r\nC. elegans nematodes on the basis of age and size. The separation\r\nmechanism takes advantage of phenotypic differences\r\nbetween ‘adult’ and ‘juvenile’ organisms and their behaviour in\r\nmicrofluidic architectures. In brief, the microfluidic device allows\r\nworms to sort themselves in a passive manner.
» A microfluidic worm sorter.

Xize Niu, Fabrice Gielen, Joshua B. Edel and Andrew J. deMello. A microdroplet dilutor for high-throughput screening. Nature Chemistry, 2011, 3, 437-442.

Pipetting and dilution are universal processes used in chemical and biological laboratories to assay and experiment. In microfluidics such operations are equally in demand, but difficult to implement. Recently, droplet-based microfluidics has emerged as an exciting new platform for high-throughput experimentation. However, it is challenging to vary the concentration of droplets rapidly and controllably. To this end, we developed a dilution module for high-throughput screening using droplet-based microfluidics. Briefly, a nanolitre-sized sample droplet of defined concentration is trapped within a microfluidic chamber. Through a process of droplet merging, mixing and re-splitting, this droplet is combined with a series of smaller buffer droplets to generate a sequence of output droplets that define a digital concentration gradient. Importantly, the formed droplets can be merged with other reagent droplets to enable rapid chemical and biological screens. As a proof of concept, we used the dilutor to perform a high-throughput homogeneous DNA-binding assay using only nanolitres of sample.
» A microfluidic droplet dilutor
» Nature Chemistry 2011 Cover

Andrew K.L Chan, Xize Niu, Andrew J. deMello and Sergei G. Kazarian. Generation of Chemical Movies: FT-IR Spectroscopic Imaging of Segmented Flows. Analytical Chemistry, 2011, 83, 3606–3609.

We have previously demonstrated that FT-IR spectroscopic imaging can be used as a powerful, label-free detection method for studying laminar flows. However, to date, the speed of image acquisition has been too slow for the efficient detection of moving droplets within segmented flow systems. In this paper, we demonstrate the extraction of fast FT-IR images with acquisition times of 50 ms. This approach allows efficient interrogation of segmented flow systems where aqueous droplets move at a speed of 2.5 mm/s. Consecutive FT-IR images separated by 120 ms intervals allow the generation of chemical movies at eight frames per second. The technique has been applied to the study of microfluidic systems containing moving droplets of water in oil and droplets of protein solution in oil. The presented work demonstrates the feasibility of the use of FT-IR imaging to study dynamic systems with subsecond temporal resolution.

Cecchini, M. P.; Hong, J.; Lim, C.; Choo, J.; Albrecht, T.; deMello, A. J.; Edel, J. B. Ultrafast Surface Enhanced Resonance Raman Scattering Detection in Droplet-Based Microfluidic Systems. Analytical Chemistry 2011, 83, 3076–3081

The development of ultrafast Raman-based detection is one of the most interesting challenges underpinning the application of droplet-based microfluidics. Herein, we describe the use of surface-enhanced resonance Raman spectroscopy (SERRS) with submillisecond time resolution as a powerful detection tool in microdroplet reactors. Individual droplets containing silver nanoparticle aggregates functionalized with Raman reporters are interrogated and characterized by full spectra acquisitions with high spatial resolution in real time. Whereas previous works coupling SERRS with droplet-based microfluidics acquire a single spectrum over single or multiple droplets, we build upon these results by increasing our temporal resolution by 2 orders of magnitude. This allows us to interrogate multiple points within one individual droplet. The SERRS signals emitted from the aggregates are utilized to access the influence of flow rate on droplet size and throughput. Accordingly, our approach allows for high-throughput analysis that facilitates the study of other biological assays or molecular interactions.

deMello, A.; Morgan, H. 10th Anniversary Issue: UK. Lab on a Chip 2011, 11, 1191–1192

The United Kingdom has a long history of innovation and development, much of which has its roots in the Industrial Revolution of the 18th and 19th centuries. Starting with the mechanisation of the textile manufacturing industry, major advances, particularly in the mechanical and chemical engineering fields, soon followed. One of the early pioneers of mechanical systems was James Watt who made significant improvements to steam engines, turning them into reliable, powerful, energy efficient machines that would drive the manufacturing centres of the country. His partner John Roebuck was one of the early pioneers (along with figures such as William Henry Perkin) to develop new methods for the mass production of chemicals, laying the foundations for the chemical industry as we know it today. Indeed, by the end of the 19th century Britain had large industrial plants manufacturing a large array of chemicals, and was exporting products and technology all over the world.

Ryu, G.; Huang, J.; Hofmann, O.; Walshe, C. A.; Sze, J. Y. Y.; McClean, G. D.; Mosley, A.; Rattle, S. J.; deMello, J. C.; deMello, A. J.; Bradley, D. D. C. Highly sensitive fluorescence detection system for microfluidic lab-on-a-chip. Lab on a Chip 2011, 11, 1664–1670

We demonstrate a compact, low cost and practical fluorescence detection system for lab-on-a-chip applications. The system comprises a commercially available InGaN light emitting diode (501 nm) as light source, an organic or silicon photodiode detector, absorptive dye coated colour filters and linear and reflective polarisers. An injection moulded polystyrene microfluidic chip is used as the platform for fluorescence immunoassays for cardiac markers myoglobin and CK-MB. The optical limit of detection (LOD) is measured using a TransFluoSphere® suspension at 5.6 × 104 beads µl−1 which can be equated to ∼3 nM fluorescein equivalent concentration. The LOD for the human plasma immunoassays is measured as 1.5 ng ml−1 for both myoglobin and CK-MB.

Rogers, M.; Leong, C.; Niu, X.; de Mello, A.; Parker, K. H.; Boutelle, M. G. Optimisation of a microfluidic analysis chamber for the placement of microelectrodes. Physical Chemistry Chemical Physics 2011, 13, 5298–5303

The behaviour of droplets entering a microfluidic chamber designed to house microelectrode detectors for real time analysis of clinical microdialysate is described. We have designed an analysis chamber to collect the droplets produced by multiphase flows of oil and artificial cerebral spinal fluid. The coalescence chamber creates a constant aqueous environment ideal for the placement of microelectrodes avoiding the contamination of the microelectrode surface by oil. A stream of alternating light and dark coloured droplets were filmed as they passed through the chamber using a high speed camera. Image analysis of these videos shows the colour change evolution at each point along the chamber length. The flow in the chamber was simulated using the general solution for Poiseuille flow in a rectangular chamber. It is shown that on the centre line the velocity profile is very close to parabolic, and an expression is presented for the ratio between this centre line velocity and the mean flow velocity as a function of channel aspect ratio. If this aspect ratio of width/height is 2, the ratio of flow velocities closely matches that of Poiseuille flow in a circular tube, with implications for connections between microfluidic channels and connection tubing. The droplets are well mixed as the surface tension at the interface with the oil dominates the viscous forces. However once the droplet coalesces with the solution held in the chamber, the no-slip condition at the walls allows Poiseuille flow to take over. The meniscus at the back of the droplet continues to mix the droplet and acts as a piston until the meniscus stops moving. We have found that the no-slip conditions at the walls of the chamber, create a banding effect which records the history of previous drops. The optimal position for sensors is to be placed at the plane of droplet coalescence ideally at the centre of the channel, where there is an abrupt concentration change leading to a response time ≪16 ms, the compressed frame rate of the video. Further away from this point the response time and sensitivity decrease due to convective dispersion.

Yamazaki, M.; Hofmann, O.; Ryu, G.; Xiaoe, L.; Lee, T. K.; deMello, A. J.; deMello, J. C. Non-emissive colour filters for fluorescence detection. Lab on a Chip 2011, 11, 1228–1233

We describe a simple technique for fabricating non-emissive colour filters based on the sensitisation of a highly porous nanostructured metal-oxide film with a monolayer of dye molecules. Ultrafast electron transfer at the oxide/dye interface induces efficient quenching of photogenerated excitons in the dye, reducing the photoluminescence quantum yield by many orders of magnitude. The resultant filters exhibit much less autofluorescence than conventional colour filters (where the chromophore is dispersed in a glass or polymer host), and are a viable low cost alternative to interference filters for microfluidic devices and other applications requiring non-emissive filtering.

Salehi-Reyhani, A.; Kaplinsky, J.; Burgin, E.; Novakova, M.; deMello, A. J.; Templer, R. H.; Parker, P.; Neil, M. A. A.; Ces, O.; French, P.; Willison, K. R.; Klug, D. A first step towards practical single cell proteomics: a microfluidic antibody capture chip with TIRF detection. Lab on a Chip 2011, 11, 1256–1261

We have developed a generic platform to undertake the analysis of protein copy number from single cells. The approach described here is ‘all-optical’ whereby single cells are manipulated into separate analysis chambers using an optical trap; single cells are lysed by a shock wave caused by laser-induced microcavitation, and the protein released from a single cell is measured by total internal reflection microscopy as it is bound to micro-printed antibody spots within the device. The platform was tested using GFP transfected cells and the relative precision of the measurement method was determined to be 88%. Single cell measurements were also made on a breast cancer cell line to measure the relative levels of unlabelled human tumour suppressor protein p53 using a chip incorporating an antibody sandwich assay format. These results suggest that this is a viable method for measuring relative protein levels in single cells.

2010

Miller, P. W.; Audrain, H.; Bender, D.; deMello, A. J.; Gee, A. D.; Long, N. J.; Vilar, R. Rapid Carbon-11 Radiolabelling for PET Using Microfluidics. Chemistry - A European Journal 2011, 17, 460–463

Positron emission tomography (PET) is an imaging technique routinely used for screening, diagnosing and staging chronic conditions such as cancer and neurodegenerative diseases. In addition to clinical applications, PET is also widely used to gain a fundamental understanding of the underlying biology of these diseases and to discover new treatments. All PET scans require a positron emitting radioisotope to enter the body, usually in the form of an injected radiopharmaceutical. The synthesis, preparation and purification of radiopharmaceuticals for PET imaging are not easy processes

Srisa-Art, M.; deMello, A. J.; Edel, J. B. High-Efficiency Single-Molecule Detection within Trapped Aqueous Microdroplets. The Journal of Physical Chemistry B 2010, 114, 15766–15772

Aqueous droplets were used as a tool to confine a molecular population and enable highly efficient detection at the single-molecule level. Picoliter-sized aqueous droplets were generated using classical multiphase microfluidics with an aqueous stream containing the analyte under investigation and an oil carrier phase. The droplets were then localized and isolated in specially designed trapping areas within the microfluidic channel to provide a static environment for detection of the encapsulated molecules. We show that by continuously flowing the carrier oil phase while holding the aqueous stationary, we can significantly improve on measuring repeat single-molecule events. Further, we find that the flowing oil stream induces a circulation within the trapped droplets which is proportional to the volumetric flow velocity. This circulation phenomenon allows a given molecule to be detected multiple times during an experiment and can therefore be used for performing time-dependent single-molecule analysis.

Casadevall i Solvas, X.; deMello, A. Droplet microfluidics: recent developments and future applications. Chemical Communications 2011, 47, 1936–1942

We report recent advances in the field of droplet-based microfluidics. Specifically, we highlight the unique features of such platforms for high-throughput experimentation; describe functional components that afford complex analytical processing and report on applications in synthesis, high-throughput screening, cell biology and synthetic and systems biology. Issues including the integration of high-information content detection methods, long term droplet stability and opportunities for large scale and intelligent biological experimentation are also discussed.

deMello, A. J.; Woolley, A. T. Nanotechnology. Current Opinion in Chemical Biology 2010, 14, 545–547

Over the past few decades the concept of miniaturization has been earnestly applied to chemical and biological problems. For example, much interest has been focused on the development of lab-on-a-chip or microfluidic technology. Largely, this has been driven by a need to accomplish rapid analysis of the small sample volumes that are typical in genomics, drug discovery, high-throughput screening and medical diagnostics. However, at a basic level, the appeal of microfluidic technology has been motivated by the fact that physical processes can be more easily controlled, accelerated and exploited when instrumental dimensions are reduced to a micron or submicron scale. The idea of miniaturization, pushed to an even greater extreme, has led to the emergence of the field of nanotechnology. Approaching the nanometer scale, bulk properties start to give way to molecular and atomic interactions, often leading to novel phenomena. The past decade has seen enormous growth in our understanding of and ability to characterize objects with nanometer-range dimensions. Importantly, these recent advances in nanoscience now show great promise in a diverse array of endeavors such as drug delivery, electronics, optical detection and sensing. The current issue highlights some of the emerging themes in the fields of micro- and nanotechnology and provides a glimpse of how the concept of miniaturization is beginning to impact chemical and biological sciences.

Gielen, F.; Pereira, F.; deMello, A. J.; Edel, J. B. High-Resolution Local Imaging of Temperature in Dielectrophoretic Platforms. Analytical Chemistry 2010, 82, 7509–7514

The use of dielectrophoretic forces is crucially tied to the knowledge of Joule heating within a fluid, since the use of planar microelectrodes creates a temperature gradient within which the particle of interest is manipulated. Mapping temperature with sufficient spatial resolution within a dielectrophoretic trap is recognized to be of high importance. Herein, we demonstrate local temperature measurements in the vicinity of a trapped micrometer-size particle using confocal fluorescence spectroscopy. Such measurements are shown to provide a novel calibration tool for screening temperature-mediated processes with high resolution.

Hong, J.; Choi, M.; Edel, J. B.; deMello, A. J. Passive self-synchronized two-droplet generation. Lab on a Chip 2010, 10, 2702–2709

We describe the use of two passive components to achieve controllable and alternating droplet generation in a microfluidic device. The approach overcomes the problems associated with irregularities in channel dimensions and fluid flow rates, and allows precise pairing of alternating droplets in a high-throughput manner. We study droplet generation and self-synchronization in a quantitative fashion by using high-speed image analysis.

Vijayakumar, K.; Gulati, S.; deMello, A. J.; Edel, J. B. Rapid cell extraction in aqueous two-phase microdroplet systems. Chemical Science 2010, 1, 447–452

Distinguishing specific cells is an essential technique in cell research and clinical diagnostics. We report a novel method to passively isolate and extract cells in a microfluidic device. We utilise a droplet-based microfluidic system to generate an aqueous two phase system in which aqueous droplets consist of two phases in the form of a double emulsion. Specifically, we generate PEG droplets that completely encapsulate DEX droplets within a microfluidic channel. Target cells can be introduced directly into the droplets and driven to partition to the more favourable phase, whilst still being contained within the aqueous droplet. Human T lymphoma cells, with diameters in the range of 10–15 μm, are chosen as a model cell line to demonstrate the partitioning.
» Chemical Science 2010 Cover

W. Miller, P.; J. deMello, A.; D. Gee, A. Application of Microfluidics to the Ultra-Rapid Preparation of Fluorine-18 Labelled Compounds. Current Radiopharmaceuticalse 2010, 3, 254–262

For over a decade the chemical, biological and analytical sciences have exploited microfluidic technology for applications ranging from cell culture to DNA amplification and analysis. More recently, microfluidic technology has been applied to the rapid synthesis of radiolabelled compounds and radiopharmaceuticals used in positron emission tomography (PET). Interest in the application of microfluidics for high speed radiolabelling stems from the inherent advantages such miniaturised reaction environments have over conventional methods. This mini-review introduces, to the nonspecialist, the extensive area of microfluidics and some of the main challenges associated with radiolabelling procedures using short-lived positron emitting isotopes. It will include a discussion of the application of microfluidics for 18F radiolabelling reactions; an area that is relatively immature. The field of PET imaging is currently growing rapidly, with increasing demand for the production of existing PET tracers and the creation of new ones. It is widely expected that microfluidic technologies will make an important contribution to improving radiotracer synthesis for PET imaging.

Krishnadasan, S.; Yashina, A.; deMello, A. J.; deMello, J. C. Microfluidic Reactors for Nanomaterial Synthesis. Micro Systems and Devices for (Bio)chemical Processes. In Advances in Chemical Engineering; Elsevier, 2010; Vol. 38, pp. 195–231 ISBN 9780123744586

The difficulty of preparing nanomaterials in a controlled, reproducible manner is a key obstacle to the proper exploitation of many nanoscale phenomena. An automated chemical reactor capable of producing (on demand and at the point of need) high-quality nanomaterials, with optimized physicochemical properties, would find numerous applications in nanoscale science and technology, especially in the areas of photonics, optoelectronics, bio-analysis, and targeted drug-delivery. In addition such a device would find immediate and important applications in toxicology, where it is essential to characterize the physiological effects of nanoparticles not only in terms of chemical composition but also in terms of size, shape, and surface functionalization. In this chapter, we describe recent advances in the development of microfluidic reactors for controlled nanoparticle synthesis and, more specifically, work in our group aimed at developing just such an automated reactor.

Chan, K. L. A.; Niu, X.; de Mello, A. J.; Kazarian, S. G. Rapid prototyping of microfluidic devices for integrating with FT-IR spectroscopic imaging. Lab on a Chip 2010, 10, 2170–2174

A versatile approach for the rapid prototyping of microfluidic devices suitable for use with FT-IR spectroscopic imaging is introduced. Device manufacture is based on the direct printing of paraffin onto the surface of an infrared transparent substrate, followed by encapsulation. Key features of this approach are low running costs, rapid production times, simplicity of design modifications and suitability for integration with FT-IR spectroscopic measurements. In the current experiments, the minimum width of channel walls was found to be ∼120 μm and ∼200 when a 25 μm and 12 μm spacer is used, respectively. Water and poly(ethylene glycol) are used as model fluids in a laminar flow regime, and are imaged in both transmission and attenuated total reflection (ATR) modes. It is established that adoption of transmission mode measurements yields superior sensitivity whilst the ATR mode is more suitable for quantitative analysis using strong spectral absorption bands. Results indicate that devices manufactured using this approach are suitable for use with in situ FT-IR spectroscopic imaging.

Wootton, R. C. R.; deMello, A. J. Microfluidics: Exploiting elephants in the room. Nature 2010, 464, 839–840

Microfluidic devices have many applications in chemistry and biology, but practical hitches associated with their use are often overlooked. One such device that optimizes catalysts tackles these issues head-on.

Casadevall i Solvas, X.; Srisa-Art, M.; deMello, A. J.; Edel, J. B. Mapping of Fluidic Mixing in Microdroplets with 1 μs Time Resolution Using Fluorescence Lifetime Imaging. Analytical Chemistry 2010, 82, 3950–3956

Microdroplets generated in microfluidic channels hold great promise for use as substrates in high-throughput chemical and biological analysis. These water-in-oil compartments can serve as isolated reaction vessels, and since they can be generated at rates in excess of 1 kHz, thousands of assays can be carried out quickly and reproducibly. Nevertheless, sampling the large amount of information generated from these platforms still remains a significant challenge. For example, considering the high droplet generation rates and velocities, reproducibility and micrometer resolution are challenging requirements that must be fulfilled. Herein we combine confocal fluorescence lifetime imaging microscopy with a statistical implementation that permits the analysis of mixing phenomena within microdroplets with a temporal resolution of 1 μs. Importantly, such exquisite resolution is only possible as a result of the large number of droplets sampled and their high structural reproducibility.

Hong, J.; deMello, A. J.; Jayasinghe, S. N. Bio-electrospraying and droplet-based microfluidics: control of cell numbers within living residues. Biomedical Materials 2010, 5, 021001

Bio-electrospraying (BES) has demonstrated great promise as a rapidly evolving strategy for tissue engineering and regenerative biology/medicine. Since its discovery in 2005, many studies have confirmed that cells (immortalized, primary and stem cells) and whole organisms (Danio rerio, Xenopus tropicalis, Caenorhabditis elegans to Drosophila) remain viable post-bio-electrospraying. Although this bio-protocol has achieved much, it suffers from one crucial problem, namely the ability to precisely control the number of cells within droplets and or encapsulations. If overcome, BES has the potential to become a high-efficiency biotechnique for controlled cell encapsulation, a technique most useful for a wide range of applications in biology and medicine ranging from the forming of three-dimensional cultures to an approach for treating diseases such as type I diabetes. In this communication, we address this issue by demonstrating the coupling of BES with droplet-based microfluidics for controlling live cell numbers within droplets and residues.

Stanley, C. E.; Elvira, K. S.; Niu, X. Z.; Gee, A. D.; Ces, O.; Edel, J. B.; deMello, A. J. A microfluidic approach for high-throughput droplet interface bilayer (DIB) formation. Chemical Communications 2010, 46, 1620–1622

We present a simple, automated method for high-throughput formation of droplet interface bilayers (DIBs) in a microfluidic device. We can form complex DIB networks that are able to fill predefined three dimensional architectures. Moreover, we demonstrate the flexibility of the system by using a variety of lipids including 1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC).
» Chemical Communications 2010 Cover

Lim, C.; Hong, J.; Chung, B. G.; deMello, A. J.; Choo, J. Optofluidic platforms based on surface-enhanced Raman scattering. The Analyst 2010, 135, 837–844

We report recent progress in the development of surface-enhanced Raman scattering (SERS)-based optofluidic platforms for the fast and sensitive detection of chemical and biological analytes. In the current context, a SERS-based optofluidic platform is defined as an integrated analytical device composed of a microfluidic element and a sensitive Raman spectrometer. Optofluidic devices for SERS detection normally involve nanocolloid-based microfluidic systems or metal nanostructure-embedded microfluidic systems. In the current review, recent advances in both approaches are surveyed and assessed. Additionally, integrated real-time sensing systems that combine portable Raman spectrometers with microfluidic devices are also reviewed. Such real-time sensing systems have significant utility in environmental monitoring, forensic science and homeland defense applications.
» Analyst 2010 Cover

2009

Miller, P.; Jennings, L.; deMello, A.; Gee, A.; Long, N.; Vilar, R. A Microfluidic Approach to the Rapid Screening of Palladium-Catalysed Aminocarbonylation Reactions. Advanced Synthesis & Catalysis 2009, 351, 3260–3268

The evaluation and selection of the most appropriate catalyst for a chemical transformation is an important process in many areas of synthetic chemistry. Conventional catalyst screening involving batch reactor systems can be both time‐consuming and expensive, resulting in a large number of individual chemical reactions. Continuous flow microfluidic reactors are increasingly viewed as a powerful alternative format for reacting and processing larger numbers of small‐scale reactions in a rapid, more controlled and safer fashion. In this study we demonstrate the use of a planar glass microfluidic reactor for performing the three‐component palladium‐catalysed aminocarbonylation reaction of iodobenzene, benzylamine and carbon monoxide to form N‐benzylbenzamide, and screen a series of palladium catalysts over a range of temperatures. N‐Benzylbenzamide product yields for this reaction were found to be highly dependent on the nature of the catalyst and reaction temperature. The majority of catalysts gave good to high yields under typical flow conditions at high temperatures (150 °C), however the palladium(II) chloride‐Xantphos complex [PdCl2(Xantphos)] proved to be far superior as a catalyst at lower temperatures (75–120 °C). The utilised method was found to be an efficent and reliable way for screening a large number of palladium‐catalysed carbonylation reactions and may prove useful in screening other gas/liquid phase reactions.

Srisa-Art, M.; deMello, A. J.; Edel, J. B. High-throughput confinement and detection of single DNA molecules in aqueous microdroplets. Chemical Communications 2009, 6548–6550

A droplet-based microfluidic system combined with high-sensitivity optical detection is used as a tool for high-throughput confinement and detection of single DNA molecules.

Srisa-Art, M.; Bonzani, I. C.; Williams, A.; Stevens, M. M.; deMello, A. J.; Edel, J. B. Identification of rare progenitor cells from human periosteal tissue using droplet microfluidics. The Analyst 2009, 134, 2239–2245

The isolation and characterisation of single cells from a heterogeneous population are important processes in cell biology, immunology, stem cell research, and cancer research. In the development of novel cell-based therapies, there is a considerable need to target specific cell types to allow for further analysis and amplification ex vivo. We introduce, herein, the use of droplet-based microfluidics as a platform technology for the identification and quantification of distinct cell phenotypes. Using molecular labelling of specific cell populations by antibodies and fluorescent dyes, detection of single cells encapsulated within picolitre-sized aqueous droplets can be performed using high-sensitivity confocal fluorescence detection. Specifically, rare progenitor cells were immunodetected within a heterogeneous population of cells isolated from human periosteal tissue. Using this model human cell population, the accuracy and reproducibility of the droplet system were tested and the results were verified using conventional flow cytometry. It was found that the quantitation of phenotypic subpopulations measured using both techniques is directly comparable. Accordingly, this study demonstrates the biological capacity of droplet-based microfluidics for cellular analysis and provides a necessary first step towards the development of a novel cell sorting technology.

Robinson, T.; Schaerli, Y.; Wootton, R.; Hollfelder, F.; Dunsby, C.; Baldwin, G.; Neil, M.; French, P.; deMello, A. Removal of background signals from fluorescence thermometry measurements in PDMS microchannels using fluorescence lifetime imaging. Lab on a Chip 2009, 9, 3437–3441

We report a method for removing unwanted contributions to fluorescence signals from dyes absorbed in polydimethylsiloxane (PDMS) using fluorescence lifetime imaging microscopy (FLIM). By analysing experimental fluorescence decays using a bi-exponential decay model, we are able to discriminate between emission originating from dye molecules in free solution and those absorbed within the PDMS substrate. Simple image processing allows the unwanted background signal to be removed and thus enables a more accurate assessment of temperature. The efficacy of the approach is demonstrated by measuring temperature changes within a droplet-based PCR device.

Niu, X. Z.; Zhang, B.; Marszalek, R. T.; Ces, O.; Edel, J. B.; Klug, D. R.; deMello, A. J. Droplet-based compartmentalization of chemically separated components in two-dimensional separations. Chemical Communications 2009, 6159–6161

We demonstrate that nanolitre-sized droplets are an effective tool in coupling two-dimensional separations in both time and space. Using a microfluidic droplet connector, chemically separated components can be segmented into nanolitre droplets. After oil filtering and droplet merging, these droplets are loaded into a second dimension for comprehensive separations.

Hong, J.; Choi, M.; deMello, A. J.; Edel, J. B. Interfacial Tension-Mediated Droplet Fusion in Rectangular Microchannels. BIOCHIP JOURNAL 2009, 3, 203–207

We successfully demonstrate the merging of aqueous droplets within a microfluidic channel mediated by a difference in interfacial tension. Interfacial tension is shown to have a significant influence on the hydrodynamic forces associated with a segmented flow in a rectangular microchannel and results in the possibility of merging multiple droplets in a simple fashion. This facility is important in allowing droplet-based microfluidic systems to be used as synthetic tools in complex reaction processing.

Chan, K. L. A.; Gulati, S.; Edel, J. B.; de Mello, A. J.; Kazarian, S. G. Chemical imaging of microfluidic flows using ATR-FTIR spectroscopy. Lab on a Chip 2009, 9, 2909–2913

Elucidating the chemical composition of microfluidic flows is crucial in both understanding and optimising reactive processes within small-volume environments. Herein we report the implementation of a novel detection methodology based on Attenuated Total Reflection (ATR)–Fourier Transform Infra-Red (FTIR) spectroscopic imaging using an infrared focal plane array detector for microfluidic applications. The method is based on the combination of an inverted prism-shape ATR crystal with a poly(dimethylsiloxane)-based microfluidic mixing device. To demonstrate the efficacy of this approach, we report the direct measurement and imaging of the mixing of two liquids of different viscosities and the imaging and mixing of H2O and D2O with consecutive H/D isotope exchange. This chemically specific imaging approach allows direct analysis of fluid composition as a function of spatial position without the use of added labels or dyes, and can be used to study many processes in microfluidics ranging from reactions to separations.

Niu, X.; Gielen, F.; deMello, A. J.; Edel, J. B. Electro-Coalescence of Digitally Controlled Droplets. Analytical Chemistry 2009, 81, 7321–7325

In this paper we describe a universal mechanism for merging multiple aqueous microdroplets within a flowing stream consisting of an oil carrier phase. Our approach involves the use of both a pillar array acting as a passive merging element, as well as built-in electrodes acting as an active merging element. The pillar array enables slowing down and trapping of the droplets via the drainage of the oil phase. This brings adjacent droplets into close proximity. At this point, an electric field applied to the electrodes breaks up the thin oil film surrounding the droplets resulting in merging.

Srisa-Art, M.; Kang, D.-K.; Hong, J.; Park, H.; Leatherbarrow, R. J.; Edel, J. B.; Chang, S.-I.; deMello, A. J. Analysis of Protein-Protein Interactions by Using Droplet-Based Microfluidics. ChemBioChem 2009, 10, 1605–1611

Every little drop: The KD values of angiogenin (ANG) interactions as shown by FRET analysis of thousands of pL-sized droplets agree with data from bulk-fluorescence polarization measurements. Importantly, the use of fluorophores does not affect the activity of ANG or the binding of anti-ANG antibodies to ANG. Such an experimental platform could be applied to the high-throughput analysis of protein–protein interactions.
» ChemBioChem 2009 Cover

Gulati, S.; Rouilly, V.; Niu, X.; Chappell, J.; Kitney, R. I.; Edel, J. B.; Freemont, P. S.; deMello, A. J. Opportunities for microfluidic technologies in synthetic biology. Journal of The Royal Society Interface 2009, 6, S493–S506

We introduce microfluidics technologies as a key foundational technology for synthetic biology experimentation. Recent advances in the field of microfluidics are reviewed and the potential of such a technological platform to support the rapid development of synthetic biology solutions is discussed.

Cullen, C. J.; Wootton, R. C. R.; de Mello, A. J. Alkene epoxidation with a polystyrene immobilised metal salen catalyst in a continuous-flow microfluidic reactor. Journal of Applied Physics 2009, 105, 102007

The epoxidation of styrene using a modularly constructed polymer immobilized Mn(III)-salen catalyst has been demonstrated within a continuous-flow glass fabricated microfluidic reactor.

Wang, X.; Amatatongchai, M.; Nacapricha, D.; Hofmann, O.; de Mello, J. C.; Bradley, D. D. C.; de Mello, A. J. Thin-film organic photodiodes for integrated on-chip chemiluminescence detection – application to antioxidant capacity screening. Sensors and Actuators B: Chemical 2009, 140, 643–648

We demonstrate that solution processed thin-film organic photodiodes (OPDs) can be used as compact and sensitive integrated detectors for antioxidant capacity screening. The OPDs were fabricated with blends of regioregular poly(3-hexylthiophene) (P3HT) and (6,6)-phenyl C61 butyric-acid methyl-ester (PCBM). The devices had a broadband photoresponse from 350 nm to 650 nm with a peak responsivity of 0.25 A/W at 550 nm and a dark current density of 0.59 μA/cm2 under 10 mV bias for a device area of 1 mm2. The signal rise and fall times of the detectors were 0.51 μs and 0.66 μs, respectively. The detectors were applied to an on-chip peroxyoxalate chemiluminescence (PO-CL) assay for antioxidant capacity determination. Antioxidant standards were injected into a stream of PO-CL reagents, resulting in a CL emission decrease that correlated with the antioxidant capacity. For the encountered CL signals the OPDs provided a comparable response to photomultiplier tubes (PMTs) commonly used in analytical applications. Antioxidant capacity screening results showed excellent consistency between the two detection methods. The compact and portable detection system is suited not only to low-cost in-the-field antioxidant capacity screening, but could have wider applications for chemiluminescence based diagnostic tests at the point-of-care.

Wang, G.; Lim, C.; Chen, L.; Chon, H.; Choo, J.; Hong, J.; deMello, A. J. Surface-enhanced Raman scattering in nanoliter droplets: towards high-sensitivity detection of mercury (II) ions. Analytical and Bioanalytical Chemistry 2009, 394, 1827–1832

We report a new method for the trace analysis of mercury (II) ions in water. The approach involves the use of droplet-based microfluidics combined with surface-enhanced Raman scattering (SERS) detection. This novel combination provides both fast and sensitive detection of mercury (II) ions in water. Specifically, mercury (II) ion detection is performed by using the strong affinity between gold nanoparticles and mercury (II) ions. This interaction causes a change in the SERS signal of the reporter molecule rhodamine B that is a function of mercury (II) ion concentration. To allow both reproducible and quantitative analysis, aqueous samples are encapsulated within nanoliter-sized droplets. Manipulation of such droplets through winding microchannels affords rapid and efficient mixing of the contents. Additionally, memory effects, caused by the precipitation of nanoparticle aggregates on channel walls, are removed since the aqueous droplets are completely isolated by a continuous oil phase. Quantitative analysis of mercury (II) ions was performed by calculating spectral peak area of rhodamine B at 1,647 cm−1. Using this approach, the calculated concentration limit of detection was estimated to be between 100 and 500 ppt. Compared with fluorescence-based methods for the trace analysis of mercury (II) ions, the detection sensitivities were enhanced by approximately one order of magnitude. The proposed analytical method offers a rapid and reproducible trace detection capability for mercury (II) ions in water.

Pereira, F.; Hassard, S.; Hassard, J.; deMello, A. CE of dsDNA in low-molecular-weight polyethylene oxide solutions. ELECTROPHORESIS 2009, 30, 2100–2109

To realise effective size separations of nucleic acid fragments using CE, gel‐based matrices are commonly employed. The separation of label‐free dsDNA ladders and plasmid fragments in an uncross‐linked semi‐dilute poly (ethylene) oxide solution using multi‐pixel UV detection at 254 nm is reported. Improvements in the sensitivity of UV detection of dsDNA using signal averaging over multiple pixels is demonstrated. Separations performed using a diode array detector also allow the progress of the separation to be monitored as a function of time. Several polymers were examined including methyl cellulose, linear polyacrylamide, hydroxy (propyl) methylcellulose and polyethylene oxide. Operations parameters investigated included UV transparency, self‐coating capacity and separation efficiency. The results show complete resolution of all fragments under a range of conditions, including short separation lengths.

Hong, J.; Paik, H.; Hwang, H.; Lee, S.; deMello, A. J.; No, K. The effect of growth temperature on physical properties of heavily doped ZnO:Al films. physica status solidi (a) 2009, 206, 697–703

Heavily‐doped ZnO:Al films have been deposited on high temperature stable glass substrates using radio‐frequency (RF) magnetron sputtering. The effect of growth temperature on physical properties of the films has been investigated. The microstructure evolved a columnar structure into a granular one with the increase in growth temperature and then a typical honeycomb‐type microstructure representing huge grain formation indicating high densification. All Al‐doped ZnO films exhibited high optical transparency and the absorption edge shifted to the short wavelength (blue‐shift) as the growth temperature increased. The dense microstructure with a high crystallographic quality and large grains evolved at 500 °C enabled us to obtain 2.28 × 10–3 Ω cm and high visible transmittance over 90% even if the ZnO film was doped with an Al content of approximately 5.5 at%. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

deMello, A. J.; Wootton, R. C. R. Miniaturization: Chemistry at the crossroads. Nature Chemistry 2009, 1, 28–29

The quest for miniaturization of chemical reactors is leading to a tangled web of reaction vessels, each formed at the junction of polymer nanofibres.

Lanigan, P. M. P.; Ninkovic, T.; Chan, K.; de Mello, A. J.; Willison, K. R.; Klug, D. R.; Templer, R. H.; Neil, M. A. A.; Ces, O. A microfluidic platform for probing single cell plasma membranes using optically trapped Smart Droplet Microtools (SDMs). Lab on a Chip 2009, 9, 1096–1101

We recently introduced a novel platform based upon optically trapped lipid coated oil droplets (Smart Droplet Microtools—SDMs) that were able to form membrane tethers upon fusion with the plasma membrane of single cells. Material transfer from the plasma membrane to the droplet via the tether was seen to occur. Here we present a customised version of the SDM approach based upon detergent coated droplets deployed within a microfluidic format. These droplets are able to differentially solubilise the plasma membrane of single cells with spatial selectivity and without forming membrane tethers. The microfluidic format facilitates separation of the target cells from the bulk SDM population and from downstream analysis modules. Material transfer from the cell to the SDM was monitored by tracking membrane localized EGFP.

Schaerli, Y.; Wootton, R. C.; Robinson, T.; Stein, V.; Dunsby, C.; Neil, M. A. A.; French, P. M. W.; deMello, A. J.; Abell, C.; Hollfelder, F. Continuous-Flow Polymerase Chain Reaction of Single-Copy DNA in Microfluidic Microdroplets. Analytical Chemistry 2009, 81, 302–306

We present a high throughput microfluidic device for continuous-flow polymerase chain reaction (PCR) in water-in-oil droplets of nanoliter volumes. The circular design of this device allows droplets to pass through alternating temperature zones and complete 34 cycles of PCR in only 17 min, avoiding temperature cycling of the entire device. The temperatures for the applied two-temperature PCR protocol can be adjusted according to requirements of template and primers. These temperatures were determined with fluorescence lifetime imaging (FLIM) inside the droplets, exploiting the temperature-dependent fluorescence lifetime of rhodamine B. The successful amplification of an 85 base-pair long template from four different start concentrations was demonstrated. Analysis of the product by gel-electrophoresis, sequencing, and real-time PCR showed that the amplification is specific and the amplification factors of up to 5 × 106-fold are comparable to amplification factors obtained in a benchtop PCR machine. The high efficiency allows amplification from a single molecule of DNA per droplet. This device holds promise for convenient integration with other microfluidic devices and adds a critical missing component to the laboratory-on-a-chip toolkit.
» Continuous flow PCR in droplets

Xize Niu, Fabrice Gielen, Andrew J. deMello, Joshua B. Edel. A Hybrid Microfluidic Chip for Digital Electro-Coalescence of Droplets. Micro Total Analysis Systems 2009
Robert Jarvis, Xize Niu, A. Mello, M. Wainwright, R. Wootton. A microfluidic flow system for activity screening of Photo-Dynamic Therapy agents. Micro Total Analysis Systems 2009
Monpichar Srisa-Art, Dong-Ku Kang, Jongin Hong, Hyun Park, Joshua B. Edel, Soo-lk Park, Andrew J. deMello. Analysis of Angiogenin-Antiangiogenin Antibody Interactions Using Droplet-Based Microfluidics. Micro Total Analysis Systems 2009
Hvangah Chon, Sangyeop Lee, Eun Su Chung, Dong-Ku Kang, Soo-Ik Chang, Jongin Hong, Andrew J. deMello, Jaebum Choo. Highly Sensitive Immunoassay Using Surface-Enhanced Raman Scattering of Hollow Gold Nanospheres in a Microfluidic Channel. Micro Total Analysis Systems 2009
Andrew de Mello. High-Throughput Chemistry and Biology: Photons, Particles and Droplets. Micro Total Analysis Systems 2009
Chaesung Lim , Juhui Ko , Guoqing Wang , Lingxin Chen , Andrew J. deMello , Jongin Hong , Jaebum Choo. Surface-Enhanced Raman Scattering in Picoliter Droplets: Towards Highly Sensitive and Selective Detection of Mercury Ions. Micro Total Analysis Systems 2009
Edel, J. B.; deMello, A. J. Chapter 7. Nanopore-Based Optofluidic Devices for Single Molecule Sensing. In Nanoscience & Nanotechnology Series; Edel, J., deMello, A., Eds.; Royal Society of Chemistry: Cambridge, 2008; pp. 139–155 ISBN 9780854041473

2008

Hong, J.; Edel, J. B.; deMello, A. J. Micro- and nanofluidic systems fo high-throughput biological screening. Drug Discovery Today 2009, 14, 134–146

High-throughput screening (HTS) is a method of scientific experimentation widely used in drug discovery and relevant to the fields of biology. The development of micro- and nanofluidic systems for use in the biological sciences has been driven by a range of fundamental attributes that accompany miniaturization and massively parallel experimentation. We review recent advances in both arraying strategies based on nano/microfluidics and novel nano/microfluidic devices with high analytical throughput rates.

Huebner, A.; Bratton, D.; Whyte, G.; Yang, M.; deMello, A. J.; Abell, C.; Hollfelder, F. Static microdroplet arrays: a microfluidic device for droplet trapping, incubation and release for enzymatic and cell-based assays. Lab on a Chip 2009, 9, 692–698

We describe the design, fabrication and use of a single-layered poly(dimethylsiloxane) microfluidic\\r\\nstructure for the entrapment and release of microdroplets in an array format controlled entirely by liquid flow. Aqueous picoliter droplets are trapped en masse and optically monitored for extended periods of time. Such an array-based approach is used to characterize droplet shrinkage, aggregation of encapsulated E. coli cells and enzymatic reactions. We also demonstrate that trapped droplets may be recovered from the microfluidic array for further processing.

Gielen, F.; deMello, A. J.; Cass, T.; Edel, J. B. Increasing the Trapping Efficiency of Particles in Microfluidic Planar Platforms by Means of Negative Dielectrophoresis. The Journal of Physical Chemistry B 2009, 113, 1493–1500

We present a novel planar electrode geometry in which particles (typically 10 μm in diameter) are focused near a defined surface before being trapped using negative dielectrophoresis. The focusing element can deflect particles having speeds up to hundreds of micrometers per second. This trapping configuration results in improved trapping yields and a decrease in overall reagent consumption. Particles are trapped dynamically while flowing in a microfluidic channel.

Niu, X.; Gulati, S.; Edel, J. B.; deMello, A. J. Pillar-induced droplet merging in microfluidic circuits. Lab on a Chip 2008, 8, 1837–1841

A novel method is presented for controllably merging aqueous microdroplets within segmented flow microfluidic devices. Our approach involves exploiting the difference in hydrodynamic resistance of the continuous phase and the surface tension of the discrete phase through the use of passive structures contained within a microfluidic channel. Rows of pillars separated by distances smaller than the representative droplet dimension are installed within the fluidic network and define passive merging elements or chambers. Initial experiments demonstrate that such a merging element can controllably adjust the distance between adjacent droplets. In a typical scenario, a droplet will enter the chamber, slow down and stop. It will wait and then merge with the succeeding droplets until the surface tension is overwhelmed by the hydraulic pressure. We show that such a merging process is independent of the inter-droplet separation but rather dependent on the droplet size. Moreover, the number of droplets that can be merged at any time is also dependent on the mass flow rate and volume ratio between the droplets and the merging chamber. Finally, we note that the merging of droplet interfaces occurs within both compressing and the decompressing regimes.
» Pillar-induced droplet merging in a microfluidic channel

Huebner, A.; Olguin, L. F.; Bratton, D.; Whyte, G.; Huck, W. T. S.; de Mello, A. J.; Edel, J. B.; Abell, C.; Hollfelder, F. Development of Quantitative Cell-Based Enzyme Assays in Microdroplets. Analytical Chemistry 2008, 80, 3890–3896

We describe the development of an enzyme assay inside picoliter microdroplets. The enzyme alkaline phosphatase is expressed in Escherichia coli cells and presented in the periplasm. Droplets act as discrete reactors which retain and localize any reaction product. The catalytic turnover of the substrate is measured in individual droplets by monitoring the fluorescence at several time points within the device and exhibits kinetic behavior similar to that observed in bulk solution. Studies on wild type and a mutant enzyme successfully demonstrated the feasibility of using microfluidic droplets to provide time-resolved kinetic measurements.

Srisa-Art, M.; Dyson, E. C.; deMello, A. J.; Edel, J. B. Monitoring of Real-Time Streptavidin-Biotin Binding Kinetics Using Droplet Microfluidics. Analytical Chemistry 2008, 80, 7063–7067

Rapid kinetic measurements are important in understanding chemical interactions especially for biological molecules. Herein, we present a droplet-based microfluidic platform to study streptavidin−biotin binding kinetics with millisecond time resolution. With integration of a confocal fluorescence detection system, individual droplets can be monitored and characterized online to extract kinetic information. Using this approach, binding kinetics between streptavidin and biotin were observed via fluorescence resonance energy transfer. The binding rate constant of streptavidin and biotin was found to be in a range of 3.0 × 106−4.5 × 107 M−1 s−1.

Robinson, T.; Valluri, P.; Manning, H. B.; Owen, D. M.; Munro, I.; Talbot, C. B.; Dunsby, C.; Eccleston, J. F.; Baldwin, G. S.; Neil, M. A. A.; de Mello, A. J.; French, P. M. W. Three-dimensional molecular mapping in a microfluidic mixing device using fluorescence lifetime imaging. Optics Letters 2008, 33, 1887–1889

Fluorescence lifetime imaging (FLIM) is used to quantitatively map the concentration of a small molecule in three dimensions in a microfluidic mixing device. The resulting experimental data are compared with computational fluid-dynamics (CFD) simulations. A line-scanning semiconfocal FLIM microscope allows the full mixing profile to be imaged in a single scan with submicrometer resolution over an arbitrary channel length from the point of confluence. Following experimental and CFD optimization, mixing times down to 1.3±0.4 ms were achieved with the single-layer microfluidic device.

Lanigan, P. M. P.; Chan, K.; Ninkovic, T.; Templer, R. H.; French, P. M. W.; de Mello, A. J.; Willison, K. R.; Parker, P. J.; Neil, M. a. A.; Ces, O.; Klug, D. R. Spatially selective sampling of single cells using optically trapped fusogenic emulsion droplets: a new single-cell proteomic tool. Journal of The Royal Society Interface 2008, 5, S161–S168

We present a platform for the spatially selective sampling of the plasma membrane of single cells. Optically trapped lipid-coated oil droplets (smart droplet microtools, SDMs), typically 0.5–5 mm in size, composed of a hexadecane hydrocarbon core and fusogenic lipid outer coating (mixture of 1,2-dioleoyl-phosphatidylethanolamine and 1,2-dioleoyl-sn-glycero-3- phosphatidylcholine) were brought into controlled contact with target colon cancer cells leading to the formation of connecting membrane tethers. Material transfer from the cell to the SDM across the membrane tether was monitored by tracking membrane-localized enhanced green fluorescent protein.

Srisa-Art, M.; deMello, A. J.; Edel, J. B. Fluorescence Lifetime Imaging of Mixing Dynamics in Continuous-Flow Microdroplet Reactors. Physical Review Letters 2008, 101, 014502

Water-in-oil microdroplets within fluidic channels have the potential to serve as isolated reaction compartments for monitoring real-time dynamics with high efficiency and repeatability. Droplets, usually generated from aqueous and oil solutions using standard microfluidic formats, can be produced at frequencies in excess of 1 kHz. Although mixing within such microdroplets is normally enhanced by chaotic advection, the mixing pattern from droplet to droplet is almost identical and reproducible in form. Herein, we demonstrate that fluorescence lifetime imaging can be used to reconstruct mixing patterns within a droplet with a time resolution of 5 μs.

Huebner, A.; Sharma, S.; Srisa-Art, M.; Hollfelder, F.; Edel, J. B.; deMello, A. J. Microdroplets: A sea of applications?. Lab on a Chip 2008, 8, 1244–1254

The exploitation of microdroplets produced within microfluidic environments has recently emerged as a new and exciting technological platform for applications within the chemical and biological sciences. Interest in microfluidic systems has been stimulated by a range of fundamental features that accompany system miniaturization. Such features include the ability to process and handle small volumes of fluid, improved analytical performance when compared to macroscale analogues, reduced instrumental footprints, low unit cost, facile integration of functional components and the exploitation of atypical fluid dynamics to control molecules in both time and space. Moreover, microfluidic systems that generate and utilize a stream of sub-nanolitre droplets dispersed within an immiscible continuous phase have the added advantage of allowing ultra-high throughput experimentation and being able to mimic conditions similar to that of a single cell (in terms of volume, pH, and salt concentration) thereby compartmentalizing biological and chemical reactions. This review provides an overview of methods for generating, controlling and manipulating droplets. Furthermore, we discuss key fields of use in which such systems may make a significant impact, with particular emphasis on novel applications in the biological and physical sciences.

Hong, J.; Lee, Y.; Chansin, G. A. T.; Edel, J. B.; deMello, A. J. Design of a solid-state nanopore-based platform for single-molecule spectroscopy. Nanotechnology 2008, 19, 165205

We numerically assess the light propagation and distribution characteristics of electromagnetic fields on nanopores formed in dielectric and metal/dielectric membranes using a frequency-domain finite element method (3D full-wave electromagnetic field simulation). Results of such studies were used to identify aluminum as an ideal material for use in optically thick metal/dielectric membranes. The comparison between SiN and Al/SiN membranes (with and without a submicron sized aperture) was numerically and experimentally shown to verify the effect of optically thick metal layers on light propagation and fluorescence excitation. The cut-off behavior for Al/SiN membranes with varying pore diameters was investigated in terms of light propagation, distribution of electromagnetic fields, and light attenuation characteristics.

Koc, Y.; de Mello, A. J.; McHale, G.; Newton, M. I.; Roach, P.; Shirtcliffe, N. J. Nano-scale superhydrophobicity: suppression of protein adsorption and promotion of flow-induced detachment. Lab on a Chip 2008, 8, 582–586

Wall adsorption is a common problem in microfluidic devices, particularly when proteins are used. Here we show how superhydrophobic surfaces can be used to reduce protein adsorption and to promote desorption. Hydrophobic surfaces, both smooth and having high surface roughness of varying length scales (to generate superhydrophobicity), were incubated in protein solution. The samples were then exposed to flow shear in a device designed to simulate a microfluidic environment. Results show that a similar amount of protein adsorbed onto smooth and nanometer-scale rough surfaces, although a greater amount was found to adsorb onto superhydrophobic surfaces with micrometer scale roughness. Exposure to flow shear removed a considerably larger proportion of adsorbed protein from the superhydrophobic surfaces than from the smooth ones, with almost all of the protein being removed from some nanoscale surfaces. This type of surface may therefore be useful in environments, such as microfluidics, where protein sticking is a problem and fluid flow is present. Possible mechanisms that explain the behaviour are discussed, including decreased contact between protein and surface and greater shear stress due to interfacial slip between the superhydrophobic surface and the liquid.

Hofmann, O.; Bradley, D. D. C.; Mello, A. J.; Mello, J. C. Lab-on-a-Chip Devices with Organic Semiconductor-Based Optical Detection. In Organic Semiconductors in Sensor Applications; Bernards, D. A., Malliaras, G. G., Owens, R. M., Eds.; Springer Berlin Heidelberg: Berlin, Heidelberg, 2008; Vol. 107, pp. 97–140 ISBN 9783540763130

In this chapter we describe the use of organic semiconductor-based light sources and photodiodes for integrated optical detection in lab-on-a-chip devices. The application of this low-cost detection technology to portable diagnostic devices for the point-of-care is also outlined.

2007

Srisa-Art, M.; deMello, A. J.; Edel, J. B. High-Throughput DNA Droplet Assays Using Picoliter Reactor Volumes. Analytical Chemistry 2007, 79, 6682–6689

The online characterization and detection of individual droplets at high speeds, low analyte concentrations, and perfect detection efficiencies is a significant challenge underpinning the application of microfluidic droplet reactors to high-throughput chemistry and biology. Herein, we describe the integration of confocal fluorescence spectroscopy as a high-efficiency detection method for droplet-based microfluidics. Issues such as surface contamination, rapid mixing, and rapid detection, as well as low detections limits have been addressed with the approach described when compared to conventional laminar flow-based fluidics. Using such a system, droplet size, droplet shape, droplet formation frequencies, and droplet compositions can be measured accurately and precisely at kilohertz frequencies. Taking advantage of this approach, we demonstrate a high-throughput biological assay based on fluorescence resonance energy transfer (FRET). By attaching a FRET donor (Alexa Fluor 488) to streptavidin and labeling a FRET acceptor (Alexa Fluor 647) on one DNA strand and biotin on the complementary strand, donor and acceptor molecules are brought in proximity due to streptavidin−biotin binding, resulting in FRET. Fluorescence bursts of the donor and acceptor from each droplet can be monitored simultaneously using separate avalanche photodiode detectors operating in single photon counting mode. Binding assays were investigated and compared between fixed streptavidin and DNA concentrations. Binding curves fit perfectly to Hill−Waud models, and the binding ratio between streptavidin and biotin was evaluated and found to be in agreement with the biotin binding sites on streptavidin. FRET efficiency for this FRET pair was also investigated from the binding results. Efficiency results show that this detection system can precisely measure FRET even at low FRET efficiencies.

Chansin, G. A. T.; Mulero, R.; Hong, J.; Kim, M. J.; deMello, A. J.; Edel, J. B. Single-Molecule Spectroscopy Using Nanoporous Membranes. Nano Letters 2007, 7, 2901–2906

We describe a novel approach for optically detecting DNA translocation events through an array of solid-state nanopores that potentially allows for ultra high-throughput, parallel detection at the single-molecule level. The approach functions by electrokinetically driving DNA strands through sub micrometer-sized holes on an aluminum/silicon nitride membrane. During the translocation process, the molecules are confined to the walls of the nanofluidic channels, allowing 100% detection efficiency. Importantly, the opaque aluminum layer acts as an optical barrier between the illuminated region and the analyte reservoir. In these conditions, high-contrast imaging of single-molecule events can be performed. To demonstrate the efficiency of the approach, a 10 pM fluorescently labeled λ-DNA solution was used as a model system to detect simultaneous translocation events using electron multiplying CCD imaging. Single-pore translocation events are also successfully detected using single-point confocal spectroscopy.

Krishnadasan, S.; Brown, R. J. C.; deMello, A. J.; deMello, J. C. Intelligent routes to the controlled synthesis of nanoparticles. Lab on a Chip 2007, 7, 1434–1441

We describe an autonomous ‘black-box’ system for the controlled synthesis of fluorescent nanoparticles. The system uses a microfluidic reactor to carry out the synthesis and an in-line spectrometer to monitor the emission spectra of the emergent particles. The acquired data is fed into a control algorithm which reduces each spectrum to a scalar ‘dissatisfaction coefficient’ and then intelligently updates the reaction conditions in an effort to minimise this coefficient and so drive the system towards a desired goal. In the tests reported here, CdSe nanoparticles were prepared by separately injecting solutions of CdO and Se into the two inlets of a heated y-shaped microfluidic reactor. A noise-tolerant global search algorithm was then used to efficiently identify—without any human intervention—the injection rates and temperature that yielded the optimum intensity for a chosen emission wavelength.

Andrew J. deMello, Christopher J. Cullen, Robin Fortt and Robert C.R. Wootton. Microfluidic Reactors for Small Molecule and Nanomaterial Synthesis. In Handbook of Capillary and Microchip Electrophoresis and Associated Microtechniques, Third Edition; Landers, J., Ed.; CRC Press, 2007; pp. 1185–1204 ISBN 9780849333293

In 1828, when attempting to prepare ammonium cyanate from silver cyanide and ammonium chloride, Friedrich Wöhler accidentally synthesized urea. Contemporary wisdom at the time held that organic compounds could only be created from a “vital force,” which existed within living organisms. In a letter to Jöns Jakob Berzelius, Wöhler’s excitement was apparent; “I can no longer, so to speak, hold my chemical water and must tell you that I can make urea without needing a kidney, whether of man or dog; the ammonium salt of cyanic acid is urea.” Although Wöhler’s discovery was not the first synthesis of an organic compound it sparked huge interest in making organic compounds from nonliving substances and marked the beginning of organic chemistry as an academic and industrial discipline.

Huang, J.; Wang, X.; deMello, A. J.; deMello, J. C.; Bradley, D. D. C. Efficient flexible polymer light emitting diodes with conducting polymer nanodes. Journal of Materials Chemistry 2007, 17, 3551–3554

We report polymer light emitting diodes fabricated on flexible poly(ethyleneterephthalate) substrates coated with a layer of poly(3,4-ethylene-dioxythiophene) : poly(styrenesulfonate) that was lithographically patterned to define the anode structure. A blend of poly(9,9-dioctylfluorene-co-benzothiadiazole) and poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine) was then spin-coated on top as the emissive layer and the device was completed by vacuum deposition of a LiF/Al bilayer cathode. The resulting yellow light emitting diodes had typical peak power and current efficiencies of 13.7 lm W−1 and 8.8 cd A−1 respectively, which compare well with values for similar devices fabricated on ITO-coated rigid glass substrates. A maximum luminance in excess of 7300 cd m−2 was achieved.

de Mello, A. J.; Edel, J. B. Hydrodynamic focusing in microstructures: Improved detection efficiencies in subfemtoliter probe volumes. Journal of Applied Physics 2007, 101, 084903

We present a method for improving detection efficiencies in single molecule confocal fluorescence spectroscopy with subfemtoliter probe volumes within microfluidic channels. Our approach is based on hydrodynamically focusing an analyte stream within a microfluidic channel down to a width on the same order of magnitude as that of the confocal probe volume. Experiments are performed in which fluorescently labeled polystyrene microspheres (930 nm diameter) are motivated through a microchannel and passed through a focused laser beam at a variety of flow rates (0.1−11 μL/min). Hydrodynamic focusing of the analyte stream is achieved by introduction of two sheath flow streams that flank the central analyte stream. Through variation of the relative flow rates in each input stream the analyte stream can be controlled with micron resolution. A maximum hydrodynamic focusing width of 3 μm was achieved within a 50 μm wide microfluidic channel; hence, a larger proportion of molecules traveling through the microfluidic device were detected. Furthermore, simple statistical methods are used to investigate the resulting fluorescence bursts and generate single-particle burst width and burst area distributions. From these data, the total detection efficiencies are shown to be an order of magnitude better than those achievable in conventional unfocused systems.

Miller, P. W.; Long, N. J.; de Mello, A. J.; Vilar, R.; Audrain, H.; Bender, D.; Passchier, J.; Gee, A. Rapid Multiphase Carbonylation Reactions by Using a Microtube Reactor: Applications in Positron Emission Tomography 11C-Radiolabeling. Angewandte Chemie 2007, 119, 2933–2936

Im Schlauch geht\\\'s auch! Ein Palladiumkatalysator auf einem Siliciumoxidträger in einem Teflonschlauch erwies sich als einfach, kostengünstig und effizient für die carbonylierende Kreuzkupplung von Arylhalogeniden mit Aminen und radioaktiv markiertem Kohlenmonoxidgas. Bei Carbonylierungen ergab der Mikroreaktorschlauch nach kurzen Verweilzeiten (12 min) höhere Ausbeuten als Batch‐Verfahren.

Edel, J. B.; deMello, A. J. Interphoton burst recurrence times: Single cell analysis in freely flowing solutions. Applied Physics Letters 2007, 90, 053904

The authors present a simple and direct analysis method for the discrimination between different cell populations in fluidic media. The methodology is based on analysis of single particle interphoton burst recurrence times and has potential use in high precision single cell sizing and counting applications. The approach requires registration of only a few hundred photons from single fluorescent particles to distinguish between different molecular populations. The technique is simple to implement and can be designed to extract information in real time within microfluidic environments.

Huebner, A.; Srisa-Art, M.; Holt, D.; Abell, C.; Hollfelder, F.; deMello, A. J.; Edel, J. B. Quantitative detection of protein expression in single cells using droplet microfluidics. Chemical Communications 2007, 0, 1218–1220

We demonstrate that single cells can be controllably compartmentalized within aqueous microdroplets; using such an approach we perform high-throughput screening by detecting the expression of a fluorescent protein in individual cells with simultaneous measurement of droplet size and cell occupancy.

Benninger, R. K. P.; Hofmann, O.; Önfelt, B.; Munro, I.; Dunsby, C.; Davis, D. M.; Neil, M. A. A.; French, P. M. W.; de Mello, A. J. Fluorescence-Lifetime Imaging of DNA–Dye Interactions within Continuous-Flow Microfluidic Systems. Angewandte Chemie 2007, 119, 2278–2281

Licht im Tunnel: Die Kombination zeitaufgelöster Fluoreszenzbildgebung mit einem Durchfluss-Mikrofluidiksystem liefert eine leistungsfähige Methode zur Auflösung und Quantifizierung biologischer Mehrzustandssysteme mit genauer räumlicher und zeitlicher Reaktionssteuerung. Die Technik wurde zur Untersuchung von DNA-Farbstoff-Bindungswechselwirkungen genutzt.

Edel, J. B.; Lahoud, P.; Cass, A. E. G.; deMello, A. J. Discrimination between Single Escherichia coli Cells Using Time-Resolved Confocal Spectroscopy. The Journal of Physical Chemistry B 2007, 111, 1129–1134

We describe a technique for rapidly discriminating between single-cell populations within a flowing microfluidic stream. Single-cell time-correlated single-photon counting (scTCSPC) as well as photon burst spectroscopy are used to characterize individual Escherichia coli cells expressed with either green, cyano, or yellow fluorescent protein. The approach utilizes standard confocal fluorescence microscopy incorporating femtoliter detection volumes. The measured burst width characteristics are predominately governed by the fluorescence quantum yield and absorption cross section of the proteins used. It is these characteristics which were used to distinguish between cells with high precision. By utilizing scTCSPC individual fluorescence lifetimes originating from single cells could also be determined. Average fluorescence lifetimes are determined using standard deconvolution procedures. The simplicity of the approach for obtaining well-defined burst width distributions is expected to be extremely valuable for single-cell sorting experiments.

Huang, J.; Xia, R.; Kim, Y.; Wang, X.; Dane, J.; Hofmann, O.; Mosley, A.; Mello, A. J. de; Mello, J. C. de; Bradley, D. D. C. Patterning of organic devices by interlayer lithography. Journal of Materials Chemistry 2007, 17, 1043–1049

We report a new lithographic procedure that enables the patterning of as-received semiconducting polymers and small molecules at the near micron level without causing discernible degradation of the patterned material. The method involves a minimum of processing steps, requires no modification of the active layer, and is compatible with both rigid and flexible substrates. The technique makes use of an intermediate resist layer between the substrate and the active layer, i.e.underneath the active layer, and involves the simultaneous patterning of the resist and active layers in a single expose/develop step. The technique has been successfully applied to the fabrication of flexible ITO-free light-emitting diodes and photodiodes, yielding peak quantum efficiencies of 8.8 cd A−1 and 57% respectively comparable to similar devices fabricated on ITO-coated glass. It is also readily extendible to the patterning on a single substrate of multiple devices incorporating different component materials, e.g. the red, green and blue pixels of a colour display.
» Journal of Materials Chemistry 2007 Cover

Cottam, B. F.; Krishnadasan, S.; deMello, A. J.; deMello, J. C.; Shaffer, M. S. P. Accelerated synthesis of titanium oxide nanostructures using microfluidic chip. Lab on a Chip 2007, 7, 167–169

The synthesis of one-dimensional titanium oxide nanostruc- tures has been accelerated by performing the reaction in a microfluidic environment as opposed to a classical batch process.

Christopher Cullen, Matthew J. Fuchter, Robert C.R. Wootton, Anthony G.M. Barrett, Andrew J. de Mello. A Tri-Phase Catalytic Microfluidic Reactor For The Generation of Singlet Oxygen Using a Novel Immobilised Seco-Porphyrazine Catalyst. Micro Total Analysis Systems 2007
M. Srisa-Art, E.C. Dyson, A. J. deMello, J. B. Edel. High Throughput Droplet-Based DNA Assays Using Fluorescence Resonance Energy Transfer. Micro Total Analysis Systems 2007
Christopher Rowlands, Richard Winkle, Robert Wootton, Andrew de Mello. Microfluidic Reaction Optmisation Using Intelligent Feedback. Micro Total Analysis Systems 2007
M. Srisa-Art, A. J. deMello, J. B. Edel. Monitoring Mixing Dynamics Confined Within Aqueous Microdroplets With 5 us Resolution. Micro Total Analysis Systems 2007
Xuhua Wang , Maliwan Amatatongchai , Duangjai Nacapricha , Oliver Hofmann , John C. deMello , Andrew J. deMello , Donal D. C. Bradley. On-Chip Antioxidant Capacity Screening Using Integrated Low-Cost Organic Photodiodes. Micro Total Analysis Systems 2007
Guillaume A.T. Chansin , Rafael Mulero , Jongin Hong , Min Jun Kim , Andrew J. deMello , Joshua B. Edel. Towards Ultra-Fast Parallel DNA Analysis: Sub Wavelength Metallic Nanopore Arrays for High-Throughput Single Molecule Spectroscopy. Micro Total Analysis Systems 2007

2006

Amatatongchai, M.; Hofmann, O.; Nacapricha, D.; Chailapakul, O.; deMello, A. J. A microfluidic system for evaluation of antioxidant capacity based on a peroxyoxalate chemiluminescence assay. Analytical and Bioanalytical Chemistry 2006, 387, 277–285

A microfluidic system incorporating chemiluminescence detection is reported as a new tool for measuring antioxidant capacity. The detection is based on a peroxyoxalate chemiluminescence (PO-CL) assay with 9,10-bis-(phenylethynyl)anthracene (BPEA) as the fluorescent probe and hydrogen peroxide as the oxidant. Antioxidant plugs injected into the hydrogen peroxide stream result in inhibition of the CL emission which can be quantified and correlated with antioxidant capacity. The PO-CL assay is performed in 800-μm-wide and 800-μm-deep microchannels on a poly(dimethylsiloxane) (PDMS) microchip. Controlled injection of the antioxidant plugs is performed through an injection valve. Of the plant-food based antioxidants tested, β-carotene was found to be the most efficient hydrogen peroxide scavenger (SA HP of 3.27 × 10−3 μmol−1 L), followed by α-tocopherol (SA HP of 2.36 × 10−3 μmol−1 L) and quercetin (SA HP of 0.31 × 10−3 μmol−1 L). Although the method is inherently simple and rapid, excellent analytical performance is afforded in terms of sensitivity, dynamic range, and precision, with RSD values typically below 1.5%. We expect our microfluidic devices to be used for in-the-field antioxidant capacity screening of plant-sourced food and pharmaceutical supplements.

Wang, X.; Hofmann, O.; Das, R.; Barrett, E. M.; deMello, A. J.; deMello, J. C.; Bradley, D. D. C. Integrated thin-film polymer/fullerene photodetectors for on-chip microfluidic chemiluminescence detection. Lab on a Chip 2007, 7, 58–63

We report the use of solution-processed thin-film organic photodiodes for microscale chemiluminescence. The active layer of the photodiodes comprised a 1 : 1 blend by weight of the conjugated polymer poly(3-hexylthiophene) [P3HT] and [6,6]-phenyl-C61-butyric acid-methylester [PCBM]—a soluble derivative of C60. The devices had an active area of 1 mm × 1 mm, and a broad-band response from 350 to 700 nm, with an external quantum efficiency of more than 50% between 450 and 550 nm. The photodiodes have a simple layered structure that permits facile integration with planar chip-based systems. To evaluate the suitability of the organic devices as integrated detectors for microscale chemiluminescence, a peroxyoxalate based chemiluminescence reaction (PO-CL) was monitored within a poly(dimethyl-siloxane) (PDMS) microfluidic device. Quantitation of hydrogen peroxide indicated excellent linearity and yielded a detection limit of 10 µM, comparable with previously reported results using micromachined silicon microfluidic chips with integrated silicon photodiodes. The combination of organic photodiodes with PDMS microfluidic chips offers a means of creating compact, sensitive and potentially low-cost microscale CL devices with wide-ranging applications in chemical and biological analysis and clinical diagnostics.
» Lab on a Chip 2007 Cover

Brewer, P. J.; Huang, J.; Lane, P. A.; deMello, A. J.; Bradley, D. D. C.; deMello, J. C. Influence of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) in polymer LEDs. Physical Review B 2006, 74, 115202

We investigate the influence of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) on the optoelectronic properties of polymer light-emitting diodes containing poly(9,9-dioctylfluorene) (PFO). Electromodulation and \\r\\nI\\r\\nV\\r\\n luminance measurements are reported for a series of devices with bare indium tin oxide (ITO) or PEDOT:PSS-coated ITO anodes and Ba or Al cathodes. The ITO/PFO/Al, ITO/PFO/Ba, and ITO/PEDOT:PSS/PFO/Al devices all exhibit conventional field-induced electromodulation behavior, in both forward and reverse bias, consistent with the Stark effect (SE). The ITO/PEDOT:PSS/PFO/Ba devices by contrast exhibit conventional behavior only for applied biases below the flat-band voltage; at higher biases, the field-induced SE features vanish and are replaced by anomalous charge-induced electromodulation features. This anomalous behavior is observed only when PEDOT:PSS is used in conjunction with a strongly electron-injecting cathode such as Ba, and is attributed to the presence of trapped electrons at the PEDOT:PSS-emitter interface, which screen the electric field from the bulk of the device. The enhanced field at the interface increases the rate of field-assisted hole injection into the highest occupied molecular orbital (HOMO) of the PFO, resulting in lower drive voltages and increased electroluminescence efficiencies.

deMello, A. J. Control and detection of chemical reactions in microfluidic systems. Nature 2006, 442, 394–402

Recent years have seen considerable progress in the development of microfabricated systems for use in the chemical and biological sciences. Much development has been driven by a need to perform rapid measurements on small sample volumes. However, at a more primary level, interest in miniaturized analytical systems has been stimulated by the fact that physical processes can be more easily controlled and harnessed when instrumental dimensions are reduced to the micrometre scale. Such systems define new operational paradigms and provide predictions about how molecular synthesis might be revolutionized in the fields of high-throughput synthesis and chemical production.

Shalom, D.; Wootton, R. C. R.; Winkle, R. F.; Cottam, B. F.; Vilar, R.; deMello, A. J.; Wilde, C. P. Synthesis of thiol functionalized gold nanoparticles using a continuous flow microfluidic reactor. Materials Letters 2007, 61, 1146–1150

Microfluidic devices show much promise for the controlled synthesis of materials on the nanoscale. In this work the first report of a synthetic method for the preparation of nanoparticles of gold stabilized by an adsorbed monolayer of a thiol (monolayer protected clusters) using a microfluidic device is described. Improvements in monodispersity are observed relative to bulk synthetic methods.

Huang, J.; Wang, X.; Kim, Y.; deMello, A. J.; Bradley, D. D. C.; deMello, J. C. High efficiency flexible ITO-free polymer/fullerene photodiodes. Physical Chemistry Chemical Physics 2006, 8, 3904–3908

We report efficient polymer photodiodes fabricated on flexible polyethyleneterephthalate (PET)\\r\\nsubstrates. The PET substrates were coated with a layer of poly(3,4-ethylene-dioxythiophene) :\\r\\npolystyrenesulfonate (PEDOT : PSS) that was lithographically patterned to define the anode\\r\\nstructure. A blend of poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-\\r\\n(6,6)C61 (PCBM) was then spin-coated from a 1 : 1 mixture by weight of the two components in\\r\\ndichlorobenzene, and the device was completed by vacuum deposition of an aluminium electrode\\r\\nin vacuum. The resulting photodiodes had short-circuit quantum efficiencies of 45% and peak\\r\\npower efficiencies of 3%, which compare favourably with values for similar devices fabricated on\\r\\nrigid indium tin oxide (ITO) coated glass substrates.

Hofmann, O.; Wang, X.; Cornwell, A.; Beecher, S.; Raja, A.; Bradley, D. D. C.; deMello, A. J.; deMello, J. C. Monolithically integrated dye-doped PDMS long-pass filters for disposable on-chip fluorescence detection. Lab on a Chip 2006, 6, 981–987

We report the fabrication of high quality monolithically integrated optical long-pass filters, for\\\\r\\\\nuse in disposable diagnostic microchips. The filters were prepared by incorporating dye molecules\\\\r\\\\ndirectly into the microfluidic chip substrate, thereby providing a fully integrated solution that\\\\r\\\\nremoves the usual need for discrete optical filters. In brief, lysochrome dyes were added to a\\\\r\\\\npoly(dimethylsiloxane) (PDMS) monomer prior to moulding of the microchip from a structured\\\\r\\\\nSU-8 master. Optimum results were obtained using 1 mm layers of PDMS doped with\\\\r\\\\n1200 μg mL-1 Sudan II, which resulted in less than 0.01% transmittance below 500 nm (OD 4),\\\\r\\\\n>80% above 570 nm, and negligible autofluorescence. These spectral characteristics compare\\\\r\\\\nfavourably with commercially available Schott-glass long-pass filters, indicating that high quality\\\\r\\\\noptical filters can be straightforwardly integrated into the form of PDMS microfluidic chips. The\\\\r\\\\nfilters were found to be robust in use, showing only slight degradation after extended illumination\\\\r\\\\nand negligible dye leaching after prolonged exposure to aqueous solutions. The provision of\\\\r\\\\nlow cost high quality integrated filters represents a key step towards the development of\\\\r\\\\nhigh-sensitivity disposable microfluidic devices for point-of-care diagnostics.
» Lab Chip 2006 Cover

Brewer, P. J.; deMello, A. J.; deMello, J. C.; Lane, P. A.; Bradley, D. D. C.; Fletcher, R.; O’Brien, J. Influence of carrier injection on the electromodulation response of trap-rich polymer light-emitting diodes. Journal of Applied Physics 2006, 99, 114502

We investigate the influence of carrier injection on the electric field distribution in polyfluorene-based polymer light-emitting diodes containing poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS). The devices show strong charge-induced electromodulation spectra due to the accumulation of trapped electrons close to the PEDOT:PSS/polyfluorene interface. The trapped electrons cause the potential to drop preferentially at the interface, enhancing hole injection and substantially reducing the magnitude of the electric field in the bulk semiconductor. The detailed operating mechanisms of such “trap-rich” devices are poorly understood, and in this paper we perform a series of temperature-dependent current-voltage sweeps and electromodulation measurements to clarify the role of the injected charge. We find that the devices show strong field redistribution only at room temperature and that devices operating at\\r\\nlower temperatures (<100 K) resemble trap-free light-emitting diodes with a uniform electric field\\r\\nthat extends through the bulk. We consider also the effects of pixel aging and show that field\\r\\nredistribution effects are reduced after extended device operation.

Wootton, R. C. R.; deMello, A. J. A one-step protocol for the chemical derivatisation of glass microfluidic devices. Lab on a Chip 2006, 6, 471–473

A simple and robust derivatisation system for glass and silica microdevices is described. The device surface is coated in a onestep treatment with a highly cross-linked polystyrene/divinylbenzene/allylsiloxane copolymer. The surface derivatisation is highly resistant to solvents, acids, bases and oxidising or reducing agents.

Benninger, R. K. P.; Koç, Y.; Hofmann, O.; Requejo-Isidro, J.; Neil, M. A. A.; French, P. M. W.; deMello, A. J. Quantitative 3D Mapping of Fluidic Temperatures within Microchannel Networks Using Fluorescence Lifetime Imaging. Analytical Chemistry 2006, 78, 2272–2278

We describe a novel method for quantitatively mapping fluidic temperature with high spatial resolution within microchannels using fluorescence lifetime imaging in an optically sectioning microscope. Unlike intensity-based measurements, this approach is independent of experimental parameters, such as dye concentration and excitation/detection efficiency, thereby facilitating quantitative temperature mapping. Micrometer spatial resolution of 3D temperature distributions is readily achieved with an optical sectioning approach based on two-photon excitation. We demonstrate this technique for mapping of temperature variations across a microfluidic chip under different heating profiles and for mapping of the 3D temperature distribution across a single microchannel under applied flow conditions. This technique allows optimization of the chip design for miniaturized processes, such as on-chip PCR, for which precise temperature control is important.

Rupa Das , Xuhua Wang , Oliver Hofmann , Andrew C. deMello , Andrew J. deMello , Donal D.C. Bradley. High-Sensitivity Low-Cost On-Chip Chemiluminescence Detection Based on Intergrated Organic Photodiodes. Micro Total Analysis Systems 2006
Oliver Hofmann, Xuhua Wang, Alastair Cornwell, Stephen Beecher, Amal Raja, Donal D.C. Bradley, John C. deMello, Andrew J. deMello. Monolithically Integrated Dye-Doped PDMS Optical Filters for Disposable On-Chip Fluorescence Detection. Micro Total Analysis Systems 2006
Philip W. Miller , Nicholas J. Long , Andrew J. de Mello , Ramon Vilar , Jan Passchier , Antony Gee. Rapid Gas-Liquid Palladium Carbonylative Cross-Coupling Reactions Using a Glass Fabricated Microfluidic Chip for Applications In C11-Radiolabelling. Micro Total Analysis Systems 2006
Christopher Cullen, Siva Krishnadasan, Robert C.R. Wootton, Andrew J. deMello. Rapid Phase Space Surface Generation Using an Integrated Microfabricated Device Reaction Detection System and Automated Control. Micro Total Analysis Systems 2006
Yasemin Koç , Paul Roach , Carole C. Perry , Michael I. Newton , Glen McHale , Andrew deMello , Neil J. Shirtcliffe. Superhydrophobic Surfaces for Microfluidic Applications. Micro Total Analysis Systems 2006

2005

Miller, P. W.; Long, N. J.; Mello, A. J. de; Vilar, R.; Passchier, J.; Gee, A. Rapid formation of amides via carbonylative coupling reactions using a microfluidic device. Chemical Communications 2006, 0, 546–548

Carbonylative cross-coupling reactions of arylhalides to form secondary amides were rapidly carried out on a glass-fabricated microchip—the first time a microstructured device has been used to perform a gas–liquid carbonylation reaction.

Benninger, R. K. P.; Hofmann, O.; McGinty, J.; Requejo-Isidro, J.; Munro, I.; Neil, M. A. A.; deMello, A. J.; French, P. M. W. Time-resolved fluorescence imaging of solvent interactions in microfluidic devices. Optics Express 2005, 13, 6275–6285

We present the application of wide-field time-resolved fluorescence imaging methods for the study of solvent interactions and mixing in microfluidic devices. Time-resolved imaging of fluorescence polarization anisotropy allows us to image the local viscosity of fluorescein in three dimensions in order to directly monitor solvent mixing within a microfluidic channel. This provides a viscosity image acquisition time of the order of minutes, and has been applied to a steady-state laminar flow configuration. To image dynamic fluid mixing in real-time, we demonstrate high-speed fluorescence lifetime imaging at 12.3 Hz applied to DASPI, which directly exhibits a solvent viscosity-dependant fluorescence lifetime. These two methods facilitate a high degree of quantification of microfluidic flow in 3-D and/or at high speed, providing a tool for studying fluid dynamics and for developing enhanced microfluidic assays.

Hofmann, O.; Wang, X.; deMello, J. C.; Bradley, D. D. C.; deMello, A. J. Towards microalbuminuria determination on a disposable diagnostic microchip with integrated fluorescence detection based on thin-film organic light emitting diodes. Lab on a Chip 2005, 5, 863–868

As a first step towards a fully disposable stand-alone diagnostic microchip for determination of urinary human serum albumin (HSA), we report the use of a thin-film organic light emitting diode (OLED) as an excitation source for microscale fluorescence detection. The OLED has a peak emission wavelength of 540 nm, is simple to fabricate on flexible or rigid substrates, and operates at drive voltages below 10 V. In a fluorescence assay, HSA is reacted with Albumin Blue 580, generating a strong emission at 620 nm when excited with the OLED. Filter-less discrimination between excitation light and generated fluorescence is achieved through an orthogonal detection geometry. When the assay is performed in 800 µm deep and 800 µm wide microchannels on a poly(dimethylsiloxane) (PDMS) microchip at flow rates of 20 µL min−1, HSA concentrations down to 10 mg L−1 can be detected with a linear range from 10 to 100 mg L−1. This sensitivity is sufficient for the determination of microalbuminuria (MAU), an increased urinary albumin excretion indicative of renal disease (clinical cut-off levels: 15–40 mg L−1)

Brewer, P. J.; Lane, P. A.; Huang, J.; deMello, A. J.; Bradley, D. D. C.; deMello, J. C. Role of electron injection in polyfluorene-based light emitting diodes containing PEDOT:PSS. Physical Review B 2005, 71, 205209

We report electromodulation (EM) studies of polyfluorene-based light-emitting diodes containing poly(3,4-ethylene-dioxythiophene)-poly(styrene-sulfonate) (PEDOT:PSS), in which the barrier to hole injection is large (∼0.7eV). Measurements are reported on devices fabricated with aluminium and barium cathodes to provide respectively poor and efficient electron injection into the active layer. The Al devices exhibit low currents, indicating low rates of electron and hole injection, whereas the Ba devices exhibit high currents and high electroluminescence efficiencies, implying efficient injection of both electrons and holes despite the large hole injection barrier. The Al devices show conventional field-induced EM behavior consistent with the Stark effect (SE). The Ba devices show conventional SE behavior for low applied biases but, above turn-on, the (field-induced) SE features vanish, indicating suppression of the internal field, and are replaced by charge-induced bleaching and absorption features. The behavior of the devices is attributed to the presence of electron traps close to the PEDOT:PSS/organic interface. The experimental findings are consistent with earlier findings by Murata et al., Van Woudenbergh et al., Poplavskyy et al., and Lane et al.

Iles, A.; Fortt, R.; de Mello, A. J. Thermal optimisation of the Reimer–Tiemann reaction using thermochromic liquid crystals on a microfluidic reactor. Lab on a Chip 2005, 5, 540–544

Microreactors incorporating thin film resistive heating elements for continuous flow organic synthesis are presented. Internal thermal conditions were monitored in real time using reflectance spectra of temperature sensitive thermochromic liquid crystals (TLC) in a collateral microfluidic network. To demonstrate the precise temperature control provided by this method, the thermal optimisation of the Reimer–Tiemann formylation of β-naphthol was performed under hydrodynamic pumping regimes.

Huang, J.; Miller, P. F.; Wilson, J. S.; de Mello, A. J.; de Mello, J. C.; Bradley, D. D. C. Investigation of the Effects of Doping and Post-Deposition Treatments on the Conductivity, Morphology, and Work Function of Poly(3,4-ethylenedioxythiophene)/Poly(styrene sulfonate) Films. Advanced Functional Materials 2005, 15, 290–296

We investigate the influence of annealing conditions on the physical properties of thin films of poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate) (PEDOT/PSS). In particular, we describe how annealing temperature, the ambient gas, and choice of dopant affect the conductivity, morphology, and work function of the films. Two specific dopants are considered, sorbitol and glycerol, and broad guidelines are developed for using PEDOT/PSS as a hole-injection electrode in polymeric light-emitting devices, solar cells, and photodetectors.

2004

Leung, S.-A.; Winkle, R. F.; Wootton, R. C. R.; deMello, A. J. A method for rapid reaction optimisation in continuous-flow microfluidic reactors using online Raman spectroscopic detection. The Analyst 2005, 130, 46–51

An extremely rapid tool for continuous flow synthetic process optimisation is described. A microfluidic reaction system operating in continuous flow is used in conjunction with confocal Raman microscopy to afford rapid molecule synthesis and product quantitation. Accordingly, the approach allows for rapid reaction optimisation within a continuous flow system. Specifically, the catalytic oxidation of isopropyl alcohol (IPA) to acetone using tetra-N-propylammonium perruthanate (TPAP)/N-methylmorpholine N-oxide (NMO) in a radial interdigitated micromixer is studied as a model reaction system. The composition of the reaction effluent can be determined with great facility and information relating to catalyst/co-oxidant ratios, catalyst turnovers and reaction endpoints extracted. Specifically, variation of catalyst and co-oxidant volumetric flow rates between 0 and 50 µL min−1 is used to vary reactant concentrations, define reaction residence times and control product conversions between 0 and 100%. The rapid nature of the system allows chemical information to be gathered and utilised on a sub-minute timescale.

Hofmann, O.; Miller, P.; Sullivan, P.; Jones, T. S.; deMello, J. C.; Bradley, D. D. C.; deMello, A. J. Thin-film organic photodiodes as integrated detectors for microscale chemiluminescence assays. Sensors & Actuators: B. Chemical 2005, 2, 878–884

We report the use of thin-film organic photodiodes as integrated optical detectors for microscale chemiluminescence. The copper phthalocyanine–fullerene (CuPc–C60) small molecule photodiodes have an external quantum efficiency of ∼30% at 600–700 nm, an active area of 2 mm × 8 mm and a total thickness of ∼2 mm. Simple detector fabrication, based on layer-by-layer vacuum deposition, allows facile integration with planar chip-based systems. To demonstrate the efficacy of the approach, CuPc–C60 photodiodes were used to monitor a peroxyoxalate based chemiluminescence reaction (PO-CL) within a poly(dimethylsiloxane) (PDMS) microfluidic device. Optimum results were obtained for applied reagent flow rates of 25 μL/min, yielding a CL signal of 8.8 nA within 11 min. Reproducibility was excellent with typical relative standard deviations (R.S.D.) below 1.5%. Preliminary quantitation of hydrogen peroxide yielded a detection limit of ∼1 mM and linearity over at least three decades. With improved sensitivity and when combined with enzymatic assays the described integrated devices could find many applications in point-of-care diagnostics.

Auroux, P.-A.; Koc, Y.; deMello, A.; Manz, A.; Day, P. J. R. Miniaturised nucleic acid analysis. Lab on a Chip 2004, 4, 534–546

The application of micro total analysis systems has grown exponentially over the past few years, particularly diversifying in disciplines related to bioassays. The primary focus of this review is to detail recent new approaches to sample preparation, nucleic acid amplification and detection within microfluidic devices or at the microscale level. We also introduce some applications that have as yet to be explored in a miniaturised environment, but should benefit from improvements in analytical efficiency and functionality when transferred to planar-chip formats. The studies described in this review were published in commonly available journals as well as in the proceedings of three major conferences relevant to microfluidics (Micro Total Analysis Systems, Transducers and The Nanotechnology Conference and Trade Show). Although an emphasis has been placed on papers published since 2002, pertinent articles preceding this publication year have also been included.

Beard, N. P.; Edel, J. B.; deMello, A. J. Integrated on-chip derivatization and electrophoresis for the rapid analysis of biogenic amines. ELECTROPHORESIS 2004, 25, 2363–2373

We demonstrate the monolithic integration of a chemical reactor with a capillary electrophoresis device for the rapid and sensitive analysis of biogenic amines. Fluorescein isothiocyanate (FITC) is widely employed for the analysis of amino-group containing analytes. However, the slow reaction kinetics hinders the use of this dye for on-chip labeling applications. Other alternatives are available such as o-phthaldehyde (OPA), however, the inferior photophysical properties and the UV λmax present difficulties when using common excitation sources leading to a disparity in sensitivity. Consequently, we present for the first time the use of dichlorotriazine fluorescein (DTAF) as a superior in situ derivatizing agent for biogenic amines in microfluidic devices. The developed microdevice employs both hydrodynamic and electroosmotic flow, facilitating the creation of a polymeric microchip to perform both precolumn derivatization and electrophoretic analysis. The favorable photophysical properties of the DTAF and its fast reaction kinetics provide detection limits down to 1 nM and total analysis times (including on-chip mixing and reaction) of <60 s. The detection limits are two orders of magnitude lower than current limits obtained with both FITC and OPA. The optimized microdevice is also employed to probe biogenic amines in real samples.

de Mello, A. J.; Habgood, M.; Lancaster, N. L.; Welton, T.; Wootton, R. C. R. Precise temperature control in microfluidic devices using Joule heating of ionic liquids. Lab on a Chip 2004, 4, 417–419

Microfluidic devices for spatially localised heating of microchannel environments were designed, fabricated and tested. The devices are simple to implement, do not require complex manufacturing steps and enable intra-channel temperature control to within ±0.2 °C. Ionic liquids held in co-running channels are Joule heated with an a.c. current. The nature of the devices means that the internal temperature can be directly assessed in a facile manner.

Krishnadasan, S.; Tovilla, J.; Vilar, R.; deMello, A. J.; deMello, J. C. On-line analysis of CdSe nanoparticle formation in a continuous flow chip-based microreactor. Journal of Materials Chemistry 2004, 14, 2655–2660

The online analysis of cadmium selenide nanoparticle formation in continuous-flow microfluidic reactors is described. The as-produced particles exhibit sharp excitonic absorption and emission peaks (∼30–40 nm) with relatively high quantum efficiencies (∼10%). The mean size and dispersity of the particles, determined using on-line fluorescence detection, may be controlled by varying the reaction temperature and/or the flow rate. The microfluidic approach provides considerable control over nucleation/growth processes and is a promising strategy for the direct production of near-monodisperse nanoparticles without recourse to further size selection.

Brewer, P. J.; Lane, P. A.; deMello, A. J.; Bradley, D. D. C.; deMello, J. C. Internal Field Screening in Polymer Light-Emitting Diodes. Advanced Functional Materials 2004, 14, 562–570

We use electromodulation spectroscopy and modeling studies to probe the electric-field distribution in polyfluorene-based polymer light-emitting diodes containing poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate). The bulk internal field is shown to be zero under ordinary operating conditions, with trapped electrons close to the anode fully screening the bulk semiconductor from the external field. The effect has far-reaching implications for the understanding and optimization of organic devices.

Oliver Hofmann and Andrew deMello. Integrated optical detectors for point-of-care diagnostics. GIT Laboratory Journal Europe, 2004, 8, 28-29

Downsizing of analytical components allows the integration of entire diagnostic processes within credit-card sized devices. However, the realisation of portable diagnostic devices for point-of-care testing has been hampered by the lack of suitable miniaturised optical detection systems. Low-cost solution processable organic semiconductors with tuneable optical properties may provide the answer. To this end, we demonstrate the application of polymer light emitting diodes (pLEDs) and organic photodiodes as integrated detection components. As a step towards the development of disposable, quantitative diagnostic tests, a prototype comprising an analytical microchip, integrated optical detection and support electronics is presented.

John deMello and Andrew deMello. Microscale reactors: nanoscale products. Lab on a Chip, 2004, 4, 11N-15N

Nanoscale science (or nanotechnology) is the exploration and exploitation of the physical, chemical, and biological properties of systems in which phenomena length scales are comparable to the dimensions of the structure. Nanotechnology has been widely recognized as one of the key research topics of the 21st century, and one that will only realise its full potential by the development of new tools for manipulating matter at the atomic/molecular scale. Over the past decade the discovery of novel phenomena, properties and processes at the “nanoscale” has opened revolutionary opportunities for the creation of novel materials and devices with superior chemical, physical, optical, electronic and/or biological properties. Nanocrystalline semiconductors are of particular interest in this regard owing to their tuneable optical and electronic properties.1 They are seen as tailored precursors in creating functional materials for use in a variety of applications including biological sensing, optoelectronics, electroluminescent displays, fibre optic communications and lasers.

Edel, J. B.; Beard, N. P.; Hofmann, O.; deMello, J. C.; Bradley, D. D. C.; deMello, A. J. Thin-film polymer light emitting diodes as integrated excitation sources for microscale capillary electrophoresis. Lab on a Chip 2004, 4, 136–140

We report the use of a thin-film polymer light emitting diode as an integrated excitation source for microfabricated capillary electrophoresis. The polyfluorene-based diode has a peak emission wavelength of 488 nm, an active area of 40 µm × 1000 µm and a thickness of ∼2 mm. The simple layer-by-layer deposition procedures used to fabricate the polymer component allow facile integration with planar chip-based systems. To demonstrate the efficacy of the approach, the polyfluorene diode is used as an excitation source for the detection of fluorescent dyes separated on-chip by electrophoresis. Using a conventional confocal detection system the integrated pLED is successfully used to detect fluorescein and 5-carboxyfluorescein at concentrations as low as 10−6 M with a mass detection limit of 50 femtomoles. The drive voltages required to generate sufficient emission from the polymer diode device are as low as 3.7 V.

Wootton, R. C. R.; deMello, A. J. Continuous laminar evaporation: micron-scale distillation. Chemical Communications, 2004, 266–267

A procedure for the continuous purification of volatile liquids within microfluidic systems is reported.

Shee-Ann Leung, Richard F. Winkle, Robert C.R. Wootton, Andrew J. de Mello. A Method for Extremely Rapid Reaction Optimisation Using a Continuous Flow Microreactor with On-Line Raman Spectrometry. Micro Total Analysis Systems 2004
Oliver Hofmann, Paul Miller, John C. deMello, Donal D.C. Bradley, Andrew J. deMello. Integrated Optical Detection for Microfluidic Systems Using Thin-Film Polymer Light Emitting Diodes and Organic Photodiodes. Micro Total Analysis Systems 2004

2003

Leung, S.-A.; Edel, J. B.; Wootton, R. C. R.; deMello, A. J. Continuous real-time bubble monitoring in microchannels using refractive index detection. Measurement Science and Technology 2004, 15, 290–296

A novel approach to the monitoring and analysis of bubbles in gas/liquid binary systems is described. The method is based on the varying extent of refraction experienced by radiation as it passes through a gas or liquid. Specifically, carbonated liquids are hydrodynamically motivated through a microfluidic channel network (40 µm wide and 30 µm deep) and directed through the path of laser beam. As a gas bubble passes through this region, the reduction in local refractive index leads to an increased displacement of the laser beam which is monitored using a position-sensitive detector. Statistical analysis of multiple bubble events (in terms of autocorrelation curves, burst width distributions and interburst time curves) yields information relating to both the bubble size and the frequency of bubble formation.

Edel, J. B.; de Mello, A. J. Determination of single particle flow velocities in microchannels using a maximum likelihood estimator method. Physical Chemistry Chemical Physics 2003, 5, 3973–3978

A statistical method based on the maximum likelihood estimator is used in order to discriminate between single particle flow velocities using confocal spectroscopy. Particles or molecules travelling at specific flow rates through a confocal volume are expected to have a definable burst widths, heights, and areas. Hence, single particles travelling with different velocities should be distinguishable based on such parameters. With this approach we show that for particles travelling with a flow rate difference of 20×, there is virtually a 0% error rate in assigning a particle to a given flow velocity, based on the analysis of a single fluorescence burst. When a flow rate difference of 4× is used, 90% of the particles travelling through the confocal probe volume are still assigned a correct flow velocity. Use of this method technique allows a statistically meaningful flow velocity to be assigned from the analysis of a photon burst from a single particle.

Edel, J. B.; Mello, A. J. de. Single Particle Confocal Fluorescence Spectroscopy in Microchannels: Dependence of Burst Width and Burst Area Distributions on Particle Size and Flow Rate. Analytical Sciences 2003, 19, 1065–1069

This article presents a non-invasive, optical technique for measuring particulate flow within microfluidic channels. Confocal fluorescence detection is used to probe single fluorescently labeled microspheres (200-930 nm diameter) passing through a focused laser beam at a variety of flow rates (100-1000 nL/min). Simple statistical methods are subsequently used to investigate the resulting fluorescence bursts and generate single-particle burst width and burst area distributions. Analysis of such distributions demonstrates that the average burst width and burst area decrease as particle size increases. In addition, both burst width and burst area (for a given particle size) are observed to decrease as volumetric flow rate is increased. The dependence of such distributions on particle size is proposed as a potential route to sizing single particles and molecules in microfluidic systems.

Fortt, R.; Wootton, R. C. R.; de Mello, A. J. Continuous-Flow Generation of Anhydrous Diazonium Species:  Monolithic Microfluidic Reactors for the Chemistry of Unstable Intermediates. Organic Process Research & Development 2003, 7, 762–768

Monolithic microfluidic reactors for the safe, expedient, and continuous synthesis of products involving unstable intermediates were fabricated and assessed. The formation of diazonium salts in anhydrous conditions and their subsequent in situ chlorination within microfluidic channels under hydrodynamic pumping regimes is presented. Significant enhancements in yield were observed due to enhanced heat and mass transfer in microfluidic systems. Analysis performed using off-line GC and GC−MS was compared with on-line, on-chip Raman spectroscopy for the direct determination of analytes.

Andrew J. de Mello. Seeing single molecules. Lab on a Chip, 2003, 3, 29N–34N

It is fair to say that the development of microfluidic systems for use in the physical and biological sciences has progressed at a significant rate since the early 1990\\\'s. The potential benefits afforded by system downsizing are documented and have provided persuasive reasons for the transferral of instrumentation from the macroscale to planar chip formats. For example, huge leaps in the application, flexibility and efficiency of separation techniques have been realised by miniaturising column dimensions and creating monolithic fluidic networks on planar substrates. Indeed, today almost all separation techniques based on electrophoretic or chromatographic discrimination have been successfully transferred to chip-based formats. Nevertheless, although system downsizing affords many performance gains, it also generates many new problems and challenges. Most of these are due in large part to the very small volumes encountered on the microscale. For example, the efficient delivery of fluids into microfluidic systems relies on the creation of high fidelity macro-to-micro interfaces. These are often both difficult and complex to engineer. In addition, the high surface area-to-volume ratios typical of small volume environments mean that internal surfaces play an important role in defining the achievable efficiencies in both separation and reaction systems. Another significant challenge arising directly from the adoption of small volume systems is the ability to efficiently detect analyte molecules. When performing capillary electrophoresis within chip-based microfluidic systems, injection volumes are commonly no larger than 50 pL. This means that for an analyte concentration of 10−8 mol L−1, only 3 × 105 molecules are available for separation and detection. This simple calculation demonstrates that detection is undoubtedly one of the primary issues determining the practicality and application of microfluidic systems. Indeed, it has long been accepted that the minimum size limits for most microfluidic devices are chiefly determined by capabilities of the system detector.

deMello, A. J. Microfluidics: DNA amplification moves on. Nature 2003, 422, 28–29

The polymerase chain reaction is widely used to amplify samples of DNA\\r\\nfor genetic analysis, and fast, high throughput is the ideal. Microscale,\\r\\nchip-based devices are now proving themselves in this arena.

Beard, N. P.; Zhang, C.-X.; deMello, A. J. In-column field-amplified sample stacking of biogenic amines on microfabricated electrophoresis devices. ELECTROPHORESIS 2003, 24, 732–739

A novel method for performing in-column field-amplified sample stacking (FASS) in chip-based electrophoretic systems is presented. The methodology involves the use of a narrow sample channel (NSC) injector. NSC injectors allow sample plugs to be introduced directly into the separation channel, and subsequent stacking and separation can proceed without any need for leakage control. More importantly, stacking and separation occur in a single step negating the requirement for complex channel geometries and voltage switching to control sample plugs during the stacking procedure. The chip is composed of six paralleled systems. Using the NSC injector design, the number of reservoirs in the multiplexed chip is reduced to N + 2, where N is the number of paralleled systems. This design feature radically reduces the complexity in chip structures and associated chip operation. The approach is applied to the analysis of fluorescently labelled biogenic amines affording detection at concentrations down to 20 pM.

de Mello, A. J.; Beard, N. Dealing with ‘real’ samples: sample pre-treatment in microfluidic systems. Lab on a Chip 2003, 3, 11N–20N

Analytical chemistry is an expansive field, encompassing a myriad of methods and techniques employed to provide discrimination of an analyte of interest from its surroundings. A generic analytical procedure can be broken down into three broad categories: the analytical principle on which the measurement is based, the analytical method (i.e. the concept of optimising the conditions for the analytical principle chosen), and finally the analytical procedure (that encompasses all considerations from analyte to analytical result).

2002

Shee-Ann Leung and Andrew J. de MelloLeung, S.-A.; de Mello, A. J. Electrophoretic analysis of amines using reversed-phase, reversed-polarity, head-column field-amplified sample stacking and laser-induced fluorescence detection. Journal of Chromatography A 2002, 979, 171–178

Analytical chemistry is an expansive field, encompassing a myriad of methods and techniques employed to provide discrimination of an analyte of interest from its surroundings. A generic analytical procedure can be broken down into three broad categories: the analytical principle on which the measurement is based, the analytical method (i.e. the concept of optimising the conditions for the analytical principle chosen), and finally the analytical procedure (that encompasses all considerations from analyte to analytical result).

Edel, J. B.; deMello, A. J.; deMello, J. C. Solution-phase electroluminescence. Chemical Communications 2002, 1954–1955

We report emissive devices exhibiting electroluminescence in the solution phase. The principle operating mechanism for these devices—direct electronic carrier injection from the electrodes into the carrier bands of the dissolved polymer—resembles that of a conventional solid-state organic light-emitting diode and is distinct from the solvent-mediated electrochemical devices recently reported by Chang et al.

Leung, S.-A.; de Mello, A. J. On.column pre-concentration of alcohol dehydrogenase in capillary electrophoresis. Journal of Separation Science 2002, 25, 1346–1350

The analysis of alcohol dehydrogenase (ADH) at low concentration using capillary electrophoresis is described. Several simple and effective ways to improve detection limits and sensitivity are investigated. These include large volume sample stacking, head column field amplified sample stacking, and sweeping. Results indicate that by using a combination of head-column field amplified sample stacking and sweeping, fluorescently labelled alcohol dehydrogenase can be pre-concentrated online by dissolving samples in water or other low conductivity matrices, and injecting into a high conductivity micellar buffer. The abrupt changes in conductivity cause narrowing of the analyte length and thus enhance the detection sensitivity. Combination of this approach with laser induced fluorescence detection yields a limit of detection of 5×10–13 M. Both qualitative and quantitative aspects of this method are investigated.

Beard, N. P.; de Mello, A. J. A polydimethylsiloxane/glass capillary electrophoresis microchip for the analysis of biogenic amines using indirect fluorescence detection. ELECTROPHORESIS 2002, 23, 1722–1730

A polydimethylsiloxane-glass capillary microchip is fabricated for the rapid analysis of a mixture of common biogenic amines using indirect fluorescence detection. Using a running buffer of phosphate and 2-propanol, and Rhodamine 110 as a background fluorophore, both co-ionic and counter-ionic systems are explored. Studies demonstrate the separation and analysis of cations using indirect fluorescence detection for the first time in a chip-based system. Resulting electrophoretic separations are achieved within a few tens of seconds with detection limits of approximately 6 ν M. The reduced sample handling and rapid separations afforded by the coupling of indirect fluorescence detection with chip-based capillary electrophoresis provide a highly efficient method for the analysis and detection of molecules not possessing a chromophore or fluorophore. Furthermore, limits of detection are on a par with reported chip-based protocols that incorporate precolumn derivatisation with fluorescence detection. The current device circumvents lengthy sample preparation stages and therefore provides an attractive alternative technique for the analysis biogenic amines.

Edel, J. B.; Fortt, R.; deMello, J. C.; deMello, A. J. Microfluidic routes to the controlled production of nanoparticles. Chemical Communications 2002, 0, 1136–1137

A microfluidic procedure for the controlled production of cadmium sulfide nanoparticles is described

Bradley M. Stone and Andrew J. de Mello. Life, the universe and microfluidics. Lab on a Chip, 2002, 2, 58N–64N

Bradley M. Stone and Andrew J. de Mello ponder the fundamental question of the ‘origin of life’ in the universe, and discuss whether miniaturised analytical instruments could be put to use within instrument payloads in upcoming space missions that aim to search for biogenic precursor molecules.

Andrew J. de Mello. On-chip chromatography: the last twenty years. Lab on a Chip, 2002, 2, 48N–54N.

At its most fundamental level, the great interest in lab-on-a-chip technology stems from the inherent performance gains that arise when most analytical systems are downsized to the micron scale. It can be argued that the reduced physical size of many chip-based systems is attractive and important in niche areas, such as ‘point-of-care’ diagnostics and ‘in-the-field’ analysis, but even then performance gains determine ultimate applicability. Over the past decade, the most active field (as judged by publication output) of microsystem development has been in transferring conventional, macroscale separation techniques to planar chip formats. This in large part has been directly due to the unmistakable improvements in separation performance as system features are diminished.

de Mello, A.; Wootton, R. But what is it good for? Applications of microreactor technology for the fine chemical industry. Lab on a Chip, 2002, 2, 7N-13N

Recent years have seen great progress in the development of microfabricated systems for use in the chemical and biological sciences. Much of this development has been driven by a need to perform analytical measurements on small sample volumes. Reducing the physical size of the measurement system naturally yields advantages such as improved efficiency with respect to sample size, response times, cost per analysis, experimental throughput and automation. However, at an even more primary level, interest in miniaturised analytical systems has been stimulated by the fact that scientists can more easily control physical processes (such as chemical reactions and molecular separations) when instrumental dimensions are reduced to the micron scale.

de Mello, A. Plastic fantastic?. Lab on a Chip, 2002, 2, 31N-36N

Without doubt, the conceptualization and development of the miniaturized total chemical analysis system (μTAS) over the past decade has revolutionized the way scientists can address a variety of complex chemical and biological problems. Since Andreas Manz and Michael Widmer presented their visionary concept in 1990 the evolution of the field has occurred at a truly exponential rate. Today, Lab-on-a-Chip technologies are routinely used in a wide variety of application areas including separation science, protein analysis, process control, environmental monitoring, chemical synthesis, DNA amplification, immunoassays, DNA sequencing, and cell manipulations. The rapid acceptance of miniaturized systems for analytical and measurement applications has been motivated by a number of reasons. At a fundamental scientific level, miniaturized analysis systems exhibit clear advantages when compared to their conventional (macroscale) counterparts. These include improved efficiency with respect to sample size, response times, analytical performance, process control and throughput. Furthermore, the fabrication methods necessary to create system features on the micron scale had been defined, developed and refined within the microelectronics industry for over almost half a century. This foundation of technological expertise in bulk and surface micromachining of silicon and silicon-compatible materials very simply meant that the creation of microfluidic chip devices (containing elements such as flow-manifolds, valves, reactors, electrodes, detectors and filters) was achieved in a relatively short timescale.

Wootton, R. C. R.; Fortt, R.; de Mello, A. J. A Microfabricated Nanoreactor for Safe, Continuous Generation and Use of Singlet Oxygen. Organic Process Research & Development 2002, 6, 187–189

Singlet oxygen was effectively and safely generated in a nanoscale reactor and used for the synthesis of ascaridole. The technique allows for the generation of singlet oxygen without the inherent dangers of large quantities of oxygenated solvents. The methodology allows for facile scale-out of the process.

Wootton, R. C. R.; Fortt, R.; de Mello, A. J. On-chip generation and reaction of unstable intermediates—monolithic nanoreactors for diazonium chemistry: Azo dyes. Lab on a Chip 2002, 2, 5–7

Monolithic nanoreactors for the safe and expedient continuous synthesis of products requiring unstable intermediates were fabricated and tested by the synthesis of azo dyes under hydrodynamic pumping regimes.

Joshua B. Edel, Robin Fortt, John C. de Mello, Andrew J. de Mello. Controlled Quantum Dot Synthesis within Microfluidic Circuits. Micro Total Analysis Systems 2002
Robin Fortt, Robert CR Wootton, Andrew J. de Mello. On Chip Generation and Reaction of Unstable Intermediates: Monolithic Microreactors for Diazonium Chemistries. Micro Total Analysis Systems 2002

2001

de Mello, A. J. DNA amplification: does ‘small’ really mean ‘efficient’?. Lab on a Chip, 2001, 1, 24N-29N.

The advent of the polymerase chain reaction (PCR) has, without a shadow of a doubt, hugely accelerated the progress of studies on the genetic structure of a diversity of organisms. PCR is an enzyme catalyzed amplification technique that allows any nucleic acid sequence to be generated in vitro and in abundance. It was first reported in early 1986 at the 51st Cold Spring Harbour laboratory Symposium on Quantitative Biology by Kary Mullis, and since has become an indispensable tool in basic molecular biology, genome sequencing, clinical research and evolutionary studies.

de Mello, A. J. Miniaturization. Analytical and Bioanalytical Chemistry 2002, 372, 12–13

In his now celebrated lecture on the 29th December 1959 Richard Feynman pondered the potential of miniaturization in the physical sciences. His vision, based on known technology, examined the limits set by physical principles and proposed a variety of new nano-tools including the concept of “atom by atom” fabrication. In the intervening decades, many of these predictions have become reality; microelectronic systems have shrunk to sizes close to the molecular level, scanning probe microscopes (e.g. STM and AFM) enable us to image and manipulate individual atoms, and the molecular machinery of living systems is now being more fully understood and harnessed.

Nittis, V.; Fortt, R.; Legge, C. H.; de Mello, A. J. A high-pressure interconnect for chemical microsystem applications. Lab on a Chip 2001, 1, 148–152

A PEEK interface for use in microfluidic applications is designed, fabricated and tested. The interface allows for the facile, non-permanent coupling of standard capillary tubing to silicon/glass micromixer chips. Importantly, the interface provides for a secure connection between capillary lines and chip reservoirs without the need for any adhesive materials. Furthermore, when used in conjunction with silicon/glass micromixer chips fluidic transport is stable over a wide range of volumetric flow rates (1–1500 μL min-1), and the entire construct can be rapidly assembled and disassembled at any time during the course of experimentation.

Joshua B. Edel, Elisabeth K. Hill and Andrew J. de Mello. Velocity measurement of particulate flow in microfluidic channels using single point confocal fluorescence detection. Analyst, 2001, 126, 1953–1957.

This article presents a non-invasive, optical technique for measuring particulate flow within microfluidic channels. Confocal fluorescence detection is used to probe single fluorescently labeled microspheres (0.93 μm diameter) passing through a focused laser beam at a variety of flow rates (50 nL min-1 – 8 μL min-1). Simple statistical methods are subsequently used to investigate the resulting fluorescence bursts and generate velocity data for the flowing particles. Fluid manipulation is achieved by hydrodynamically pumping fluid through microchannels (150 μm wide and 50 μm deep) structured in a polydimethylsiloxane (PDMS) substrate. The mean fluorescence burst frequency is shown to be directly proportional to flow speed. Furthermore, the Poisson recurrence time and width of recovered autocorrelation curves is demonstrated to be inversely proportional to flow speed. The component-based confocal fluorescence detection system is simple and can be applied to a diversity of planar chip systems. In addition, velocity measurement only involves interrogation of the fluidic system at a single point along the flow stream, as opposed to more normal multiple-point measurements.

Jakeway, S. C.; Mello, A. J. de. Chip-based refractive index detection using a single point evanescent wave probe. Analyst 2001, 126, 1505–1510

This paper presents a novel approach for performing spectroscopic refractive index detection within microfluidic channel environments. Based on the principle of total internal reflection (TIR), changes in the refractive index of an analyte stream passing through a microfabricated channel are detected through interaction with an optical evanescent field formed at the channel wall. Refractive index variations within the microchannel environment modify the critical angle at the liquid–solid interface, thereby altering the characteristics of evanescent field formation in solution. These variations are evidenced through measurement of fluorescence intensities. Initially, the design and testing of the method are described. Subsequently, refractive index values for bulk sucrose solutions (0–35% w/v sucrose in water) are measured using the single point evanescent wave probe and compared with values obtained through conventional refractometry and the literature. Close agreement between all three approaches is demonstrated. The method is then applied to the detection of sucrose plugs (10–500 mM) hydrodynamically flowing through microfabricated channels on a planar glass chip. The evanescent wave probe is also used to selectively monitor specific analytes within a multicomponent system, by precise angular control in the vicinity of the critical angle. Although detection limits using the prototype system are non-ideal (∼5 µM carbohydrate), they compare favourably with existing methods for on-chip refractive index detection.

Mitchell, M. C.; Spikmans, V.; Manz, A.; de Mello, A. J. Microchip-based synthesis and total analysis systems (μSYNTAS): Chemical microprocessing for generation and analysis of compound libraries. Journal of the Chemical Society, Perkin Transactions 1 2001, 514–518

A miniaturised-SYNthesis and Total Analysis System (μSYNTAS) integrating a silicon-machined chemical microprocessor and time-of-flight mass spectrometry (TOF-MS) is used for the generation of compound libraries based on sub-reactions of an Ugi multicomponent reaction (MCR). The microreactor-based on the concept of an AND logic operator—allowed the coupling of serially-switched solution-phase library generation with on-line compound analysis and identification. In addition, the μSYNTAS allowed real-time parallel-processing of MCR sub-reactions; in contrast to combinatorial techniques employing a solid support for reagent and product isolation, the μSYNTAS protocol required no additional preparation or work-up procedures.

Sirichai, S.; de Mello, A. J. A capillary electrophoresis chip for the analysis of print and film photographic developing agents in commercial processing solutions using indirect fluorescence detection. ELECTROPHORESIS 2001, 22, 348–354

The separation and detection of both print and film developing agents (CD-3 and CD-4) in photographic processing solutions using chip-based capillary electrophoresis is presented. For simultaneous detection of both analytes under identical experimental conditions a buffer pH of 11.9 is used to partially ionise the analytes. Detection is made possible by indirect fluorescence, where the ions of the analytes displace the anionic fluorescing buffer ion to create negative peaks. Under optimal conditions, both analytes can be analyzed within 30 s. The limits of detection for CD-3 and CD-4 are 0.17 mM and 0.39 mM, respectively. The applicability of the method for the analysis of seasoned photographic processing developer solutions is also examined.

Stephen C. Jakeway, Andrew J. de Mello. A Single Point Evanescent Wave Probe for On-Chip Refractive Index Detection. Micro Total Analysis Systems 2001
de Mello, A. J. Chip-MS: Coupling the large with the small. Lab on a Chip, 2001, 1, 7N–12N

Over the past decade the miniaturization of analytical techniques and methods has become a highly visible and dominant trend in the physical and biological sciences. Development in this area has primarily been driven by a need for rapid, on-line measurements at low concentrations within fields such as DNA analysis, drug discovery, pharmaceutical screening, medical diagnostics, environmental analysis and chemical production. The advantages associated with shrinking analytical systems are well known and include improved efficiency with respect to sample size, application, response times, cost, analytical performance, integration, throughput and automation.

2000

Mitchell, M. C.; Spikmans, V.; Mello, A. J. de. Microchip-based synthesis and analysis: Control of multicomponent reaction products and intermediates. The Analyst 2001, 126, 24–27

A miniaturised-SYNthesis and Total Analysis System (μSYNTAS) was used for the solution-phase synthesis and non-line analysis (TOF-MS) of Ugi multicomponent reaction (MCR) products. This approach provides an unusually high degree of control of the MCR and delivers detailed, novel information on reaction intermediates in real-time. Specifically, the Ugi 4 component condensation (4CC) involving the reaction of an amine, acid, aldehyde an isocyanide species was performed at room temperature in a controllable fashion. Furthermore, observation of the nitrilium intermediate, cyclohexyl(2-piperidin-1-ylethylidyne)ammonium chloride, is presented for the first time.

Hill, E. K.; Mello, A. J. de. Single-molecule detection using confocal fluorescence detection: Assessment of optical probe volumes. The Analyst 2000, 125, 1033–1036

We have constructed a simple component-based confocal detection system, that is capable of fluorescence detection at the single-molecule level. The component-based format maximises flexibility and reduces start-up costs. A new model for the optical probe volume is proposed, that is based on the 1/e2 Gaussian intensity contour of a laser beam focused to the diffraction limit. Observation of the onset of single-molecule detection in our experimental system confirms that this model is more appropriate than a simple cylindrical approximation for a probe volume defined by a wide, tightly focused laser beam.

Jakeway, S. C.; de Mello, A. J.; Russell, E. L. Miniaturized total analysis systems for biological analysis. Fresenius’ Journal of Analytical Chemistry 2000, 366, 525–539

This review article discusses and documents the basic philosophies, concepts and current advances in the field of μ-TAS development, with special emphasis on applications in the arena of biosciences. After a brief overview of miniaturization theory and fabrication techniques, areas of microfluidic component development, detection protocols, biochemical assays, and integrated biological analyses are addressed.

Sirichai, S.; de Mello, A. J. A capillary electrophoresis microchip for the analysis of photographic developer solutions using indirect fluorescence detection. The Analyst 2000, 125, 133–137

A capillary electrophoresis microchip is developed for the rapid determination of 4-amino-3-methyl- N-ethyl-N-(b-methane sulfonamidoethyl)aniline (CD-3) in commercial colour photographic processing solutions and the applicability of the method is examined. The use of indirect fluorescence as an on-chip detection method is also demonstrated. Using a running buffer at pH 11.9 prepared from disodium hydrogenphosphate and fluorescein the quantitative determination of CD-3 is achieved, resulting in an analysis time of approximately 7 s. Under these conditions, a detection limit of about 5 mg L-1 is obtained, with good linearity between signal and concentration over a range of 5–20 mg L-1.

Michael C. Mitchell , Valerie Spikmans , Fiona Bessoth , Andreas Manz , Andrew de Mello. Towards organic synthesis in microfluidic devices: multicomponent reactions for the construction of compound libraries. Micro Total Analysis Systems 2000

1999

Bessoth, F. G.; deMello, A. J.; Manz, A. Microstructure for efficient continuous flow mixing. Analytical Communications 1999, 36, 213–215

This paper presents a micromixer for the laminar flow regime based on the principle of flow lamination. The structure is made up from a glass/silicon/glass sandwich, has a total internal volume of ~ 600 nL and measures 5 mm x 10 mm. Flow rates between 1–200 µL/min have successfully been used. Fluorescence quenching experiments were carried out for quantification and showed 95% mixing within 15 ms.

Mello, A. J. de; Manz, A. Chip technology for micro-separation. In Microsystem Technology; BioMethods; Birkhäuser, Basel, 1999; pp. 129–177 ISBN 9783034897846

1998

Byrne, C. D.; de Mello, A. J.; Barnes, W. L. Variable-Angle Time-Resolved Evanescent Wave-Induced Fluorescence Spectroscopy (VATR-EWIFS): A Technique for Concentration Profiling Fluorophores at Dielectric Interfaces. The Journal of Physical Chemistry B 1998, 102, 10326–10333

The concentration distributions of fluorescein and acridine orange, at a water/silica interface, are determined using the technique variable-angle time-resolved evanescent wave-induced fluorescence spectroscopy. It is demonstrated theoretically that the radiative fluorescence lifetime of a molecule is affected in only a minor way by the presence of a dielectric interface. Consequently, time-resolved evanescent wave-induced nfluorescence spectroscopy is used to measure the variations in the fluorescence quantum yield caused by the presence of the interface. Knowledge of these variations is then used to determine molecular concentration distributions. The concentration distribution of fluorescein is found to be uniform and homogeneous as a function of distance away from the hydrophilic silica surface. However, it is found that a water/silica interface has a definite affect on the concentration distribution of acridine orange. A “surface associated” acridine orange population distinguishable from “bulk” acridine orange is demonstrated by spectral and kinetic analysis of EWIF emission. This information is then used to create concentration profiles of both molecular populations.

Hill, E. K.; Mello, A. J. de; Birrell, H.; Charlwood, J.; Camilleri, P. Steady state and time-resolved fluorescence of 2-aminoacridone sugar derivatives. Journal of the Chemical Society, Perkin Transactions 2 1998, 2337–2342

The fluorescence properties of 2-aminoacridone (2-AMAC) and some polysaccharide derivatives have been studied in the steady state and with time-correlated single-photon counting. 2-AMAC in methanol has an absorption maximum at 425 nm and a fluorescence emission maximum at 530 nm. The absorption spectrum shows a sufficiently broad tail for satisfactory excitation by the light from an argon ion laser (488 nm). Lifetime decay analysis shows that the fluorescence lifetime of the aminoacridone moiety is not changed significantly by the addition of a sugar chain, or by the length or structure of that chain. 2-AMAC exhibits a fluorescence decay that may be fitted to a single exponential in both methanol (t ≈ 12 ns) and water (t ≈ 10 ns); in an equal mixture of the solvents the behaviour is best described by a sum of two exponential terms. We have also shown that the absorbance of a complex mixture of 2-AMAC tagged glycans is directly proportional to their fluorescence emission at 525 nm. These results have confirmed our previous studies that 2-AMAC is a useful and non-selective fluorescent tag in the analysis of polysaccharide chains.

Burggraf, N.; Krattiger, B.; de Rooij, N. F.; Manz, A.; de Mello, A. J. Holographic refractive index detector for application in microchip-based separation systems. The Analyst 1998, 123, 1443–1447

A novel detection scheme for capillary electrophoresis on planar glass microchips is presented. The application of a holographic-based refractive index detector to the electrophoretic separation of carbohydrates is described. The microchip device consists of a cyclic (square) separation channel having a circumference of 80 mm, a width of 40 mm and a depth of 10 µm. The volume of the injection scheme is approximately 16 pl. Separation and refractive index detection of a mixture of sucrose, N-acetylglucosamine and raffinose, each at a concentration of 33 mm, was achieved within 17 s of injection. Preliminary results demonstrate the feasibility of using hologram-based refractive index detectors in microchip separation systems. Although the initial detection limits are poor in comparison with alternative techniques, the potential of a universal detector of this kind is clear.

Byrne, C. D.; de Mello, A. J. Photophysics of ethidium bromide complexed to ct-DNA: a maximum entropy study. Biophysical Chemistry 1998, 70, 173–184

Time-integrated and time-resolved fluorescence spectroscopies have been used to probe the photophysical properties of ethidium bromide (Eb) complexed to calf thymus DNA (ct-DNA). Fluorescence decay profiles are obtained using the technique of time-correlated single photon counting (TCSPC), and subsequently analysed using conventional sum-of-exponential (SOE) routines and also the maximum entropy method (MEM). Through use of these methods and simulated decay data, it is demonstrated that the kinetics of Eb in the presence of ds-DNA are best described by a generic model consisting of three exponential terms. At all DNA:Eb ratios and NaCl concentrations studied, free Eb is detected. Furthermore, Eb is found to interact with ds-DNA through two mechanisms, each distinguishable by its fluorescence decaytime. Eb is shown to interact with DNA through classic intercalation, and also through binding at secondary sites. The component decaytimes are shown to be a function of NaCl concentration but independent of DNA:Eb molar ratio.

Kopp, M. U.; de Mello, A. J.; Manz, A. Chemical Amplification: Continuous-Flow PCR on a Chip. Science 1998, 280, 1046–1048

A micromachined chemical amplifier was successfully used to perform the polymerase chain reaction (PCR) in continuous flow at high speed. The device is analogous to an electronic amplifier and relies on the movement of sample through thermostated temperature zones on a glass microchip. Input and output of material (DNA) is continuous and amplification is independent of input concentration. A 20-cycle PCR amplification of a 176 – base pair fragment from the DNA gyrase gene of Neisseria gonorrhoeae was performed at various flow rates, resulting in total reaction times of 90 seconds to 18.7 minutes.

1997

Arora, A.; de Mello, A. J.; Manz, A. Sub-microliter Electrochemiluminescence Detector—A Model for Small Volume Analysis Systems. Analytical Communications 1997, 34, 393–395

A small volume, electrochemical cell for the generation and detection of electrochemiluminescence from tris(2,2\\\\\\\'-bipyridyl) ruthenium(II) has been fabricated. The flowcell is a poly(methyl methacrylate) (PMMA)–acetate–PMMA sandwich construct, containing two platinum, thin-film electrodes. Operation of the microchip establishes sub-microliter detection of tris(2,2\\\\\\\'-bipyridyl) ruthenium(II) electrochemiluminescence in continuous flow. Initial experiments demonstrate a detection limit of 5e-13 M at an effective cell volume of 100 nl. This corresponds to the detection of only 30 000 molecules.

1996

Woolley, A. T.; Hadley, D.; Landre, P.; deMello, A. J.; Mathies, R. A.; Northrup, M. A. Functional Integration of PCR Amplification and Capillary Electrophoresis in a Microfabricated DNA Analysis Device. Analytical Chemistry 1996, 68, 4081–4086

Microfabricated silicon PCR reactors and glass capillary electrophoresis (CE) chips have been successfully coupled to form an integrated DNA analysis system. This construct combines the rapid thermal cycling capabilities of microfabricated PCR devices (10 °C/s heating, 2.5 °C/s cooling) with the high-speed (<120 s) DNA separations provided by microfabricated CE chips. The PCR chamber and the CE chip were directly linked through a photolithographically fabricated channel filled with hydroxyethylcellulose sieving matrix. Electrophoretic injection directly from the PCR chamber through the cross injection channel was used as an “electrophoretic valve” to couple the PCR and CE devices on-chip. To demonstrate the functionality of this system, a 15 min PCR amplification of a -globin target cloned in M13 was immediately followed by high-speed CE chip separation in under 120s, providing a rapid PCR-CE analysis in under 20 min. A rapid assay for genomic Salmonella DNA was performed in under 45 min, demonstrating that challenging amplifications of diagnostically interesting targets can also be performed. Real-time monitoring of PCR target amplification in these integrated PCR-CE devices is also feasible. Amplification of the -globin target as a function of cycle number was directly monitored for two different reactions starting with 4×10^7 and 4×10^5 copies of DNA template. This work establishes the feasibility of performing high-speed DNA analyses in microfabricated integrated fluidic systems.

de Mello, A. J.; Elliott, J. A.; Rumbles, G. Evanescent wave-induced fluorescence study of Rhodamine 101 at dielectric interfaces. Journal of the Chemical Society, Faraday Transactions 1996, 92, 4723–4731

Time-integrated and time-resolved evanescent wave-induced fluorescence spectroscopies (EWIFS) have been used to probe the photophysical properties of Rhodamine 101 at two solution/solid interfaces. Interaction of Rhodamine 101 with a fused silica surface leads to a reduction in the molecular fluorescence quantum efficiency in both cases. The fluorescence kinetics of interfacial species are shown to be complex (non-exponential), a function of bulk solution concentration, and a function of distance normal to the interface. The application of the maximum entropy method to the analysis of EWIF decays is presented. Recovered lifetime distributions expose inherent complexity and heterogeneity that is hidden to conventional analysis techniques.

deMello, A. J. Chapter 1. Total Internal Reflection Fluorescence Spectroscopy. In Surface Analytical Techniques for Probing Biomaterial Processes; Davies, J. Surface Analytical Techniques for Probing Biomaterial Processes; CRC Press, 1996; ISBN 9780849383526
Rumbles, G.; Samuel, I. D. W.; Magnani, L.; Murray, K. A.; DeMello, A. J.; Crystall, B.; Moratti, S. C.; Stone, B. M.; Holmes, A. B.; Friend, R. H. Chromism and luminescence in regioregular poly(3-dodecylthiophene). Synthetic Metals 1996, 76, 47–51

We report photoluminescence studies of poly( 3-dodecylthiophene) (P3DT) in solution. In a good solvent the polymer exhibits luminescence nwith a high quantum efficiency and a decay time of 500 ps. In a poor solvent the emission is red shifted with a 20-fold reduction in nquantum efficiency and a decay profile that is non-monoexponential, but has an average lifetime that is very similar to the good solvent nenvironment. The data indicate a large increase in the natural radiative lifetime from approximately 1 ns in a good solvent to 20 ns in a poor nsolveni, which implies an emitting state that is different in the two situations. In the poor solvent the spectrum is almost identical to that of nthe thin film, suggesting that the polymer aggregates in the solution and the emitting species is the same in both environments. The data are nconsistent with the formation of an excited state that is not localized on a single chain but is delocalized over more than one chain.

1995

Dhami, S.; Mello, A. J. D.; Rumbles, G.; Bishop, S. M.; Phillips, D.; Beeby, A. PHTHALOCYANINE FLUORESCENCE AT HIGH CONCENTRATION: DIMERS OR REABSORPTION EFFECT?. Photochemistry and Photobiology 1995, 61, 341–346

For tetrasulfonated aluminum phthalocyanine (AlPcS4), dimer formation is characterized in nthe absorption spectrum by a broadening of the Q-band and the appearance of a new band a t the red nedge of the spectrum. The high concentrations required to produce dimers, however, often leads to nanomalous observations in fluorescence spectroscopy. In the present study, we have examined the nphotophysical characteristics of two dye systems; AlPcS4 in a 66% ethanol/water mixture and disulfonated naluminum phthalocyanine in methanol. Using absorption spectroscopy, the formation of dimers is shown nto be prevalent only in the case of AIPcS4. The fluorescence emission spectra in both cases, however, nexhibit similar spectral changes with increasing dye concentration. The measured fluorescence decay nprofiles for both dyes also show similar trends: They are monoexponential, invariant with emission nwavelength and have decay times that increase with dye concentration. These distortions are sometimes nincorrectly attributed to dimer fluorescence. We find no evidence for the existence of dimer fluorescence nand demonstrate that these data can be readily explained, by taking into consideration the effects of nreabsorption of fluorescence.

De Mello, A. J.; Crystall, B.; Rumbles, G. Evanescent-Wave Spectroscopic Studies of Surface-Enhanced Fluorescence Quantum Efficiencies. Journal of Colloid and Interface Science 1995, 169, 161–167

The techniques of evanescent wave induced fluorescence spectroscopy (EWIFS) and time-correlated single-photon counting have been combined to investigate the photophysical properties of auramine-O at a solid/solution interface. Interaction of the dye with the surface causes an enhancement of the fluorescence quantum efficiency through the restriction of intramolecular rotations. The fluorescence kinetics of the adsorbed molecules are shown to be a function of surface and bulk solution concentration. The application of the maximum entropy method to the analysis of EWIFS decays is also introduced and discussed