Publications

A catalogue of the deMello Group publications

2017

Yun Ding, Jaebum Choo, Andrew J. deMello. From single-molecule detection to next-generation sequencing: microfluidic droplets for high-throughput nucleic acid analysis. Microfluid Nanofluid, 2017, 21: 58.

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.

Daniel T. Chiu, Andrew J. deMello, Dino Di Carlo, Patrick S. Doyle, Carl Hansen, Richard M. Maceiczyk & Robert C.R. Wootton. Small but Perfectly Formed? Successes, Challenges, and Opportunities for Microfluidics in the Chemical and Biological Sciences. Chem 2, 2017, February 9, 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.

Richard Maceiczyk, Hisashi Shimizu, David Müller, Takehiko Kitamori, and Andrew deMello. A Photothermal Spectrometer for Fast and Background-Free Detection of Individual Nanoparticles in Flow. Anal. Chem., 2017, 89 (3), 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

Jae-Won Choi, Byung-Gwan Jo, Andrew deMello, Jaebum Choo & Hak Yong Kim. Streptavidin-triggered signal amplified fluorescence polarization for analysis of DNA-protein interaction. Analyst, 2016, 141, 6499-6520

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 binding affinity of human angiogenin and single-stranded DNA aptamer. Streptavidin was bound to biotinylated single-stranded DNA aptamer and interaction between this complex and Alexa Fluor 488 labelled human angiogenin was measured. A dissociation constant of 135.3 ± 32.9 nM and 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 molecule 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 this 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 concentration of rare and expensive protein samples.\\\\r\\\\n

Xavier Casadevall i Solvas, Andrew deMello. Particle concentration influences inertial focusing in Multiorifice Flow Fractionation microfluidic devices. Matters, 2016, 201606000007

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 components in the performances of these devices.\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\r\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n

Lukmaan A. Bawazer, Ciara S. McNally, Christopher J. Empson, William J. Marchant, Tim P. Comyn, Xize Niu, Soongwon Cho, Michael J. McPherson, Bernard P. Binks, Andrew deMello & Fiona C. Meldrum1. Combinatorial microfluidic droplet engineering for biomimetic material synthesis. Science Advances, 2016, 2, 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.

Marta Rubio-Martinez, Inhar Imaz, Neus Domingo, Afshin Abrishamkar, Tiago Sotto Mayor, René M. Rossi, Carlos Carbonell, Andrew J. deMello, David B. Amabilino, Daniel Maspoch & Josep Puigmartí-Luis. Freezing the non-classical 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.

Alexandra Yashina, Ioannis Lignos, Stavros Stavrakis, Jaebum Choo and Andrew deMello. Scalable production of CuInS2/ZnS quantum dots in a two-step droplet-based microfluidic platform. J. Mater. Chem. 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.

Chiara Martino & Andrew J. deMello. 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.

Richard M. Maceiczyk, Leonard Bezinge and Andrew J. deMello. Kinetics of nanocrystal synthesis in a microfluidic reactor: theory and experiment. React. Chem. Eng., 2016, 1, 261-271.

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

Chiara Martino, Daniele Vigolo, Xavier Casadevall i Solvas, Stavros Stavrakis and Andrew J. deMello. 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 Technology, 2016, 1, 1600025.

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.

David Müller, Stefano Cattaneo, Florian Meier, Roland Welz, Tjerk de Vries, Meital Portugal-Cohen, Diana C Antonio, Claudia Cascio, Luigi Calzolai, Douglas Gilliland, Andrew de Mello. Inverse supercritical fluid extraction as a sample preparation method for the analysis of the nanoparticle content in sunscreen agents. Journal of Chromatography A, 1140, 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.

Xiaobao Cao, Andrew deMello and Katherine S. Elvira. Enhanced versatility of fluid control on centrifugal microfluidic platforms using two degrees of freedom. Lab 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.

Yun Ding, Famin Qiu, Xavier Casadevall i Solvas, Flora Wing Yin Chiu, Bradley J. Nelson, and Andrew deMello. 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.

Ioannis Lignos, Stavros Stavrakis, Georgian Nedelcu, Loredana Protesescu, Andrew J. deMello, and Maksym V. Kovalenko. 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.

Rongke Gao, Ziyi Cheng, Andrew J. deMello and Jaebum Choo. Wash-free magnetic immunoassay of the PSA cancer marker using SERS and droplet microfluidics. Lab 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.

Afshin Abrishamkar, Markos Paradinas, Elena Bailo, Romen Rodriguez-Trujillo, Raphael Pfattner, René M. Rossi, Carmen Ocal, Andrew J. deMello, David B. Amabilino & Josep Puigmartí-Luis. Microfluidic Pneumatic Cages: A novel approach for in-chip crystal trapping, manipulation and controlled chemical treatment. J. Vis. Exp., 2016, 113, e54193.

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.

Chiara Martino, Cyril Statzer, Daniele Vigolo & Andrew J. deMello. Controllable Generation and Encapsulation of Alginate Fibers Using Droplet-Based Microfluidics. Lab 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.

Claire E. Stanley*, Guido Grossmann, Xavier Casadevall i Solvas and Andrew deMello*. Soil-on-a-Chip: Microfluidic platforms for environmental organismal studies. Lab 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.

Jae-Won Choi, Kyong-Mi Min, Sundar Hengoju, Gil-Jung Kim, Soo-Ik Chang, Andrew J. deMello, Jaebum Choo, Hak Yong Kim. A droplet-based microfluidic immunosensor for high efficiency melamine analysis. Biosensors & 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

Dong-Ku Kang, Xiuqing Gong, Soongwon Cho, Jin-young Kim, Joshua B. Edel, Soo-Ik Chang, Jaebum Choo, Andrew J. deMello. 3D Droplet Microfluidic Systems for High-Throughput Biological Experimentation. Analytical Chemistry, 2015, 87, 10770−10778

Herein, we describe the development of a multilayer droplet\r\nmicrofluidic system for creating concentration gradients and generating\r\nmicrodroplets of varying composition for high-throughput biochemical and\r\ncell-based screening applications. The 3D droplet-based microfluidic device\r\nconsists of multiple PDMS layers, which are used to generate logarithmic\r\nconcentration gradient reagent profiles. Parallel flow focusing structures are used\r\nto form picoliter-sized droplets of defined volumes but of varying composition.\r\nAs 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.

Hyangah Chon, Rui Wang, So-Young Bang, Hye-Soon Lee, Sang-Cheol Bae, Sung Hyun Hong, Young Ho Yoon, Andrew J. deMello & Jaebum Choo. Clinical validation of surface-enhanced Raman scattering-based immunoassays in the early diagnosis of rheumatoid arthritis. Analytical and Bioanalytical Chemistry

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.

Flora Wing Yin Chiu, Hakan Bagci, Amanda G. Fisher, Andrew J. deMello and Katherine S. Elvira. A microfluidic toolbox for cell fusion. Journal of Chemical Technology and 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.

David J. Collins, Adrian Neild, Andrew deMello, Ai-Qun Liu and Ye Ai . The Poisson distribution and beyond: methods for microfluidic droplet production and single cell encapsulation. Lab 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.

David Müller, Stefano Cattaneo, Florian Meier, Roland Welz & Andrew J. de Mello. Nanoparticle separation with a miniaturized asymmetrical flow field-flow fractionation cartridge. Frontiers in Chemistry 3:45. doi: 10.3389/fchem.2015.00045

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, Dirk van Swaay, Andrew deMello, Ross Anderson and Stephen Mann . 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.

Dirk van Swaay, Dora Tang, Stephen Mann and Andrew de Mello. Microfluidic Formation of Membrane-Free Aqueous Coacervate Droplets in Water. Angew. Chem. Int. Ed. 2015, 54, 1 – 5

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.

Ioannis Lignos, Stavros Stavrakis, Ardita Kilaj and Andrew J. deMello. 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.

Oliver Dressler, Tianjin Yang, Soo-Ik Chang, Jaebum Choo, Robert C. R. Wootton and Andrew deMello. 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

Carl Esben Poulsen, Robert C. R. Wootton, Anders Wolff, Andrew J. deMello and Katherine S. Elvira. A microfluidic platform for the rapid determination of distribution coefficients by gravity assisted droplet-based liquid-liquid extraction. Analytical Chemistry, 2015, 87 (12), 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.

Rongke Gao, Juhui Ko, Kiweon Cha, Jun Ho Jeon, Gi-eun Rhie, Jonghoon Choi, Andrew J. deMello and Jaebum Choo. Fast and sensitive detection of an anthrax biomarker using SERS-based solenoid microfluidic sensor. Biosens. Bioelectron., 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.

David Hess, Anandkumar Rane, Andrew J. deMello and Stavros Stavrakis. High-Throughput, Quantitative Enzyme Kinetic Analysis in Microdroplets using Stroboscopic Epifluorescence Imaging. Anal. Chem., 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.

Aaron P. Debon, Robert. C. R. Wootton and Katherine. S. Elvira. Droplet confinement and leakage: Causes, underlying effects, and amelioration strategies. Biomicrofluidics, 2015, 9, 024119

The applicability of droplet-based microfluidic systems to many research fields stems from the fact that droplets are generally considered individual and self-contained reaction vessels. This study demonstrates that, more often than not, the integrity of droplets is not complete, and depends on a range of factors including surfactant type and concentration, the micro-channel surface, droplet storage conditions, and the flow rates used to form and process droplets. Herein, a model microfluidic device is used for droplet generation and storage to allow the comparative study of forty-four different oil/surfactant conditions. Assessment of droplet stability under these conditions suggests a diversity of different droplet failure modes. These failure modes have been classified into families depending on the underlying effect, with both numerical and qualitative models being used to describe the causative effect and to provide practical solutions for droplet failure amelioration in microfluidic systems.

Tohid Pirbodaghi, Daniele Vigolo, Samin Akbari and Andrew deMello. Investigating the fluid dynamics of rapid processes within microfluidic devices using bright-field microscopy. Lab Chip, 2015, 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.

Chiara Martino, Tae Yong Lee, Shin-Hyun Kim, and Andrew deMello. Microfluidic Generation of PEG-b-PLA Polymersomes Containing Alginate-based Core Hydrogel. Biomicrofluidics, 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.

Richard M. Maceiczyk, Ioannis G. Lignos and Andrew J. deMello. Online detection and automation methods in microfluidic nanomaterial synthesis. Curr. Opin. Chem. Eng., 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.

Yun Ding, Xavier Casadevall i Solvas and Andrew deMello. The “V-junction”: a novel structure for high-speed generation of bespoke droplet flows. 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

Tom Robinson, Prashant Valluri, Gordon Kennedy, Alessandro Sardini, Christopher Dunsby, Mark A. A. Neil, Geoff S. Baldwin, Paul M. W. French, and Andrew J. de Mello. Analysis of DNA binding and nucleotide flipping kinetics using two-color two-photon fluorescence lifetime imaging microscopy. Anal. Chem., 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.

Chiara Martino, Simon Berger, Robert C. R. Wootton and Andrew J. deMello. A 3D-Printed Microcapillary Assembly for Facile Double Emulsion Generation. Lab 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.

Claire E. Stanley, Martina Stöckli, Dirk van Swaay, Jerica Sabotič, Pauli Kallio, Markus Kuenzler, Andrew deMello and Markus Aebi. Probing bacterial-fungal interactions at the single cell level. Integr. Biol., 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.

Richard M. Maceiczyk and Andrew J. deMello. Fast and Reliable Metamodeling of Complex Reaction Spaces Using Universal Kriging. J. Phys. Chem. 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.

Thomas W. Phillips*, Ioannis G. Lignos*, Richard M. Maceiczyk*, Andrew J. deMello and John C. deMello. Nanocrystal synthesis in microfluidic reactors: where next?. Lab 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.

Jae-Won Choi, Sangmin Lee, Dong-Hun Lee, Joonwon Kim, Andrew J. deMello and Soo-Ik Chang. Integrated pneumatic micro-pumps for high-throughput droplet-based microfluidics. RSC Adv., 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.

Ioannis Lignos, Loredana Protesescu, Stavros Stavrakis, Laura Piveteau, Mark J. Speirs, Maria Antonietta Loi, Maksym V. Kovalenko, and Andrew J. deMello. Facile Droplet-based Microfluidic Synthesis of Monodisperse IV–VI Semiconductor Nanocrystals with Coupled In-Line NIR Fluorescence Detection. Chem. Mater., 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.

Jin-young Kim, Soo-Ik Chang, Andrew J. deMello and Danny O’Hare. Integration of monolithic porous polymer with droplet-based microfluidics on a chip for nano/ picoliter volume sample analysis. Nano Convergence 2014, 1, 1-5

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.

Simon Berger, Joanna Stawikowska, Dirk van Swaay, and Andrew deMello. Continuous Suspension of Lipids in Oil by the Selective Removal of Chloroform via Microfluidic Membrane Separation. Ind. Eng. Chem. Res., 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.

Yan Zhao, Fiona Pereira, Andrew J. deMello, Hywel Morgan and Xize Niu. Droplet-based in situ compartmentalization of chemically separated components after isoelectric focusing in a Slipchip. Lab 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.

Xiuqing Gong, Amol V. Patil, Aleksandar P. Ivanov, Qingyuan Kong, Thomas Gibb, Fatma Dogan, Andrew J. deMello, and Joshua B. Edel . Label-Free In-Flow Detection of Single DNA Molecules using Glass Nanopipettes. Anal. Chem., 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.

Oliver J. Dressler, Richard M. Maceiczyk, Soo-Ik Chang, Andrew J. Demello. Droplet-Based Microfluidics: Enabling Impact on Drug Discovery. J. Biomol. Screen., 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

2013

Dirk van Swaay, Jean-Pierre Mächler, Claire Stanley and Andrew deMello. A chip-to-world connector with a built-in reservoir for simple small-volume sample injection. Lab Chip, 2013, 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.

Y. Ding, S. Stavrakis, X. Casadevall i Solvas, and A. 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\r\nconventional synthetic methods. These studies represent the first multiphase microfluidic method for the synthesis of diynes.

Katherine S. Elvira*, Xavier Casadevall i Solvas, Robert C. R. Wootton and Andrew J. deMello*. 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.

Xize Niu, Fiona Pereira, Joshua B. Edel, and Andrew J. de Mello. Droplet-Interfaced Microchip and Capillary Electrophoretic Separations. Anal. Chem. 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.

Soongwon Cho, Dong-Ku Kang, Steven Sim, Florian Geier, Jin-Young Kim, Xize Niu, Joshua B. Edel, Soo-Ik Chang, Robert C. R. Wootton, Katherine S. Elvira and Andrew J. deMello. 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.

Fiona Pereira, Xize Niu and Andrew J. deMello. 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.

Fabrice Gielen, Liisa Van Vliet, Bartosz T. Koprowski, Sean R.A. Devenish, Martin Fischlechner, Joshua B. Edel, Xize Niu, Andrew J. de Mello and Florian Hollfelder. A Fully Unsupervised Compartment-on-demand Platform for Precise Nanolitre Assays of Time-Dependent Steady-State Enzyme Kinetics and Inhibition. Anal. Chem., 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.

Dirk van Swaay and Andrew deMello. Microfluidic methods for forming liposomes. Lab Chip, 2013, 13, 752-767

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.

Katherine S. Elvira, Robert C. R. Wootton, Nuno M. Reis, Malcolm R. Mackley and Andrew J. deMello. Through-wall mass transport as a modality for safe generation of singlet oxygen in continuous flows. ACS Sustainable Chemistry and 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

Mikihide Yamazaki, Siva Krishnadasan, Andrew J. deMello and John C. deMello. Non-emissive plastic colour filters for fluorescence detection. Lab 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.

Xize Niu and Andrew J. deMello. Building droplet-based microfluidic systems for biological analysis. Biochem. Soc.Trans., 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.

Yuval Elani, Andrew J. deMello, Xize Niu and Oscar Ces. Novel technologies for the formation of 2-D and 3-D droplet interface bilayer networks. Lab 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.

Ioannis G. Lignos, Robert C.R. Wootton, Bradley M. Stone & Andrew J. deMello. Segmented Flow Microfluidics. Roberts GC. Encyclopedia of Biophysics. Heidelberg, Springer, 2012.

During the past two decades, the use of miniaturized systems for the manipulation and processing of fluid samples has gained significant interest because of their chemical, biological and biomedical applications. This interest in large part been driven by concomitant advances in the areas of genomics, proteomics, drug discovery, high-throughput screening and diagnostics, with a clearly defined need to perform rapid measurements on small sample volumes. At a basic level, microfluidic activities have been motivated by the fact that physical processes can be more easily controlled when instrumental dimensions are reduced to the micron scale.

Miriam S. Goyder, Keith R. Willison, David R. Klug, Andrew J. deMello and Oscar Ces. 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.

Alexandra Yashina, Fiona Meldrum and Andrew deMello. 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.

Katherine S. Elvira, Robin Leatherbarrow, Joshua Edel and Andrew deMello. 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.

Jae-Won Choi, Dong-Ku Kang, Hyun Park, Andrew J. deMello & Soo-Ik Chang. High-Throughput Analysis of Protein–Protein Interactions in Picoliter-Volume Droplets Using Fluorescence Polarization. Anal. Chem., 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.

Claire E. Stanley, Robert C. R. Wootton and Andrew J. deMello. Continuous and segmented flow microfluidics: Applications in high-throughput chemistry and biology. Chimia, 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.

Robert C.R. Wootton and Andrew J. deMello. 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.

Xiuqing Gong, Philip W. Miller, Antony D. Gee, Nicholas J. Long, Andrew J. de Mello and Ramon Vilar. Gas–Liquid Segmented Flow Microfluidics for Screening Pd-Catalyzed Carbonylation Reactions. Chem. Eur. J., 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.

Kritika Kumar, Adrian M. Nightingale, Siva H. Krishnadasan, Nazila Kamaly, Marzena Wylenzinska-Arridge, Katharina Zeissler, Will R. Branford, Ecaterina Ware, Andrew J. deMello and John C. deMello. Direct synthesis of dextran-coated superparamagnetic iron oxide nanoparticles in a capillary-based droplet reactor. J. Mater. Chem., 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
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
Fabrice Gielen, Andrew J. deMello and Joshua B. Edel. Dielectric Cell Response in Highly Conductive Buffers. Anal. Chem., 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

Soongwon Cho, Dong-Ku Kang, Jaebum Choo, Andrew J. deMello and Soo-Ik Chang. 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 chipbased microfluidic formats over the last decade, including gene sequencing, emulsion PCR, immunoassays, electrophoresis, cellbased 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.

Xavier Casadevall i Solvas, Xize Niu, Katherine Leeper, Soongwon Cho, Soo-Ik Chang, Joshua B. Edel and Andrew J. deMello. Fluorescence detection methods for microfluidic droplet platforms. J. Vis. Exp., 2011, 58, e3437

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.

Jin-young Kim, Andrew J. deMello, Soo-Ik Chang, Jongin Hong and Danny O’Hare. Thermoset polyester droplet-based microfluidic devices for high frequency generation. Lab 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 O2 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.

Guillaume A. T. Chansin, Jongin Hong, Jonathan Dusting, Andrew J. deMello, Tim Albrecht, and Joshua B. Edel. 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. Chem. Commun., 2011, 47, 9801–9803

We present a passive microfluidic strategy for sorting adult C. elegans nematodes on the basis of age and size. The separation mechanism takes advantage of phenotypic differences between ‘adult’ and ‘juvenile’ organisms and their behaviour in microfluidic architectures. In brief, the microfluidic device allows worms 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. Nat. Chem., 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. Anal. Chem. 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 dropletsmove 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.

Michael P. Cecchini, Jongin Hong, Chaesung Lim, Jaebum Choo, Tim Albrecht, Andrew J. deMello and Joshua B. Edel. Ultrafast Surface Enhanced Resonance Raman Scattering Detection in Droplet-Based Microfluidic Systems. Anal. Chem. 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.

Andrew deMello and Hywel Morgan. 10th Anniversary Issue: UK. Lab 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.

Gihan Ryu, Jingsong Huang, Oliver Hofmann, Claire A. Walshe, Jasmine Y. Y. Sze, Gareth D. McClean, Alan Mosley, Simon J. Rattle, John C. deMello, Andrew J. deMello and Donal D. C. Bradley. Highly sensitive fluorescence detection system for microfluidic lab-on-a-chip. Lab 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 5.6e4 beads/µl which can be equated to ~3 nM fluorescein equivalent concentration. The LOD for the human plasma immunoassays is measured as 1.5 ng/ml for both myoglobin and CK-MB.

Michelle Rogers, Chi Leong, Xize Niu, Andrew de Mello, Kim H. Parker and Martyn G. Boutelle. Optimisation of a microfluidic analysis chamber for the placement of microelectrodes. Phys. Chem. Chem. Phys., 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.

Mikihide Yamazaki, Oliver Hofmann, Gihan Ryu, Li Xiaoe, Tai Kyu Lee, Andrew J. deMello and John C. deMello. Non-emissive colour filters for fluorescence detection. Lab 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.

Ali Salehi-Reyhani, Joseph Kaplinsky, Edward Burgin, Miroslava Novakova, Andrew J. deMello, Richard H. Templer, Peter Parker, Mark A. A. Neil, Oscar Ces, Paul French, Keith R. Willison and David Klug. A first step towards practical single cell proteomics: a microfluidic antibody capture chip with TIRF detection. Lab 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

Philip W. Miller, Hélène Audrain, Dirk Bender, Andrew J. deMello, Antony D. Gee, Nicholas J. Long and Ramon Vilar. Rapid Carbon-11 Radiolabelling for PET Using Microfluidics. Chem. Eur. J., 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.

Monpichar Srisa-Art, Andrew J. deMello and Joshua B. Edel. High-Efficiency Single-Molecule Detection within Trapped Aqueous Microdroplets. J. Phys. Chem. 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.

Xavier Casadevall i Solvas and Andrew deMello. Droplet microfluidics: recent developments and future applications. Chem. Commun., 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.

Simon D. Brandt, Robert C. R. Wootton , et al. The Naphyrone Story: The Alpha or Beta-naphthyl Isomer?. Drug testing and Analysis

Naphyrone (naphthylpyrovalerone,O-2482) hasbeen recently advertised forpurchase on a number of websites. This compound has been viewed as a so-called ‘legal high’ and was classified as a controlled drug under the UK Misuse of Drugs Act 1971 in mid-July 2010. So far, naphyrone is commonly equated with 1-naphthalen-2-yl-2-pyrrolidin-1-yl-pentan-1-one (β-naphyrone) but analytical characterization of two naphyrone samples revealed the existence of a novel isomer consistent with 1- naphthalen-1-yl-2-pyrrolidin-1-yl-pentan-1-one (α-naphyrone). Analyses of both α- and β-naphyrone were carried out using gas chromatography ion trap (EI/CI)mass spectrometry and 1D/2D nuclear magnetic resonance spectroscopy. This provides the first report of α-naphyrone in the scientific literature and the ability to differentiate it from the β-isomer should be of interest to forensic and clinical communities.

Andrew J. deMello and Adam T Woolley. Nanotechnology. Curr. Opin. Chem. Biol., 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, highthroughput 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.

Fabrice Gielen, Fiona Pereira, Andrew J. deMello and Joshua B. Edel. High-Resolution Local Imaging of Temperature in Dielectrophoretic Platforms. Anal. Chem. 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 calibra- tion tool for screening temperature-mediated processes with high resolution.

Jongin Hong, Minsuk Choi, Joshua B. Edel and Andrew J. deMello. Passive self-synchronized two-droplet generation. Lab 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.

Kalpana Vijayakumar, Shelly Gulati, Andrew J. deMello and Joshua B. Edel. Rapid cell extraction in aqueous two-phase microdroplet systems. Chem. Sci., 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

Philip W. Miller, Andrew J. deMello and Antony D. Gee. Application of Microfluidics to the Ultra-Rapid Preparation of Fluorine-18 Labelled Compounds. Curr. Radiopharm., 2010, Vol. 3, No. 2, 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.

Siva Krishnadasan, Alexandra Yashina, Andrew J. deMello and John C. deMello. Microfluidic Reactors for Nanomaterial Synthesis. Micro Systems and Devices for (Bio)chemical Processes. Adv. Chem. Eng., 2010, 38, 195-231

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.

Andrew K. L. Chan, Xize Niu, Andrew J. de Mello and Sergei G. Kazarian. Rapid prototyping of microfluidic devices for integrating with FT-IR spectroscopic imaging. Lab 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 µm 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.

Robert C. R. Wootton and Andrew J. deMello. 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.

Xavier Casadevall i Solvas, Monpichar Srisa-Art, Andrew J. deMello and Joshua B. Edel. Mapping of Fluidic Mixing in Microdroplets with 1 μs Time Resolution Using Fluorescence Lifetime Imaging. Anal. Chem. 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.

Jongin Hong, Andrew J deMello and Suwan N Jayasinghe. Bio-electrospraying and droplet-based microfluidics: control of cell numbers within living residues. Biomed. Mater., 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.

Claire E. Stanley*, Katherine S. Elvira*, Xize Z. Niu, Antony D. Gee, Oscar Ces, Joshua B. Edel and Andrew J. deMello. 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\r\nformation of droplet interface bilayers (DIBs) in a microfluidic\r\ndevice. We can form complex DIB networks that are able to fill\r\npredefined three dimensional architectures. Moreover, we\r\ndemonstrate the flexibility of the system by using a variety of lipids\r\nincluding 1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC)\r\nand 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC).
» Chemical Communications 2010 Cover

Chaesung Lim, Jongin Hong, Bong Geun Chung, Andrew J. deMello and Jaebum Choo. Optofluidic platforms based on surface-enhanced Raman scattering. 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

Philip W. Miller, Lucy E. Jennings, Andrew J. deMello, Antony D. Gee, Nicholas J. Long, and Ramon Vilar. A Microfluidic Approach to the Rapid Screening of Palladium-Catalysed Aminocarbonylation Reactions. Adv. Synth. Catal., 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 oC), however the palladium(II) chloride-Xantphos complex [PdCl2 (Xantphos)] proved to be far superior as a catalyst at lower temperatures (75–120 oC). 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.

Monpichar Srisa-Art, Andrew J. deMello and Joshua B. Edel. High-throughput confinement and detection of single DNA molecules in aqueous microdroplets. Chem. Commun., 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.

Monpichar Srisa-Art, Ian C. Bonzani, Andrew Williams, Molly M. Stevens, Andrew J. deMello and Joshua B. Edel. Identification of rare progenitor cells from human periosteal tissue using droplet microfluidics. 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.

Tom Robinson, Yolanda Schaerli, Robert Wootton, Florian Hollfelder, Christopher Dunsby, Geoff Baldwin, Mark Neil, Paul French and Andrew deMello. Removal of background signals from fluorescence thermometry measurements in PDMS microchannels using fluorescence lifetime imaging. Lab 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.

Xize Z. Niu, B. Zhang, Rafal T. Marszalek, Oscar Ces, Joshua B. Edel, David R. Klug and Andrew J. deMello. Droplet-based compartmentalization of chemically separated components in two-dimensional separations. Chem. Commun., 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.

Ashleigh B. Theberge, Graeme Whyte, et al. Suzuki–Miyaura coupling reactions in aqueous microdroplets with catalytically active fluorous interfaces . Chemical Communications

Using microfluidic techniques and a novel fluorous-tagged palladium catalyst, we generated droplet reactors with catalytically active walls and used these compartments for small molecule synthesis.

Jongin Hong, Minsuk Choi, Andrew J. deMello and Joshua B. Edel. Interfacial Tension-Mediated Droplet Fusion in Rectangular Microchannels. Biochip J., 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.

Andrew K. L. Chan, Shelly Gulati, Joshua B. Edel, Andrew J. de Mello and Sergei G. Kazarian. Chemical imaging of microfluidic flows using ATR-FTIR spectroscopy. Lab 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.

Xize Niu, Fabrice Gielen, Andrew J. deMello and Joshua B. Edel. Electro-Coalescence of Digitally Controlled Droplets. Anal. Chem., 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.

Monpichar Srisa-Art, Dong-Ku Kang, Jongin Hong, Hyun Park, Robin J. Leatherbarrow, Joshua B. Edel, Soo-Ik Chang and Andrew J. deMello. Analysis of Protein–Protein Interactions by Using Droplet-Based Microfluidics. Chem. BioChem., 2009, 10, 1605 – 1611

One of the primary goals of current proteomics research is to understand the physiological and metabolic pathways of cells and thereby establish molecular diagnostic tools that are able to identify the proteins associated with disease states. More specifically, protein–protein interactions are critical for many biological functions. For example, signal mediation between the exterior and interior of a cell is normally a result of protein– protein interactions. Such signal transduction plays an elementary role in many biological processes and in many diseases (such as cancer). Accordingly, the ability to probe protein– protein interactions in a high-throughput manner is recognised to be important in developing effective diagnostic techniques, cultivating disease therapies and discovering new small-molecule drug candidates.
» ChemBioChem 2009 Cover

Shelly Gulati, Vincent Rouilly, Xize Niu, James Chappell, Richard I. Kitney, Joshua B. Edel, Paul S. Freemont and Andrew J. deMello. Opportunities for microfluidic technologies in synthetic biology. J. R. Soc. 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.

Christopher J. Cullen, Robert C. R. Wootton and Andrew J. de Mello. Alkene epoxidation with a polystyrene immobilised metal salen catalyst in a continuous-flow microfluidic reactor. J. Appl. Phys. 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.

Xuhua Wang, Maliwan Amatatongchai, Duangjai Nacapricha, Oliver Hofmann, John C. de Mello, Donal D.C. Bradley and Andrew J. de Mello. Thin-film organic photodiodes for integrated on-chip chemiluminescence detection – application to antioxidant capacity screening. Sens. Actuators B, 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 650nm with a peak responsivity of 0.25 A/W at 550nm and a dark current density of 0.59μA/cm2 under 10mV bias for a device area of 1mm2. The signal rise and fall times of the detectors were 0.51μs and 0.66μs, respectively. The detectorswere 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.

Guoqing Wang, Chaesung Lim, Lingxin Chen, Hyangah Chon, Jaebum Choo, Jongin Hong and Andrew J. deMello. Surface-enhanced Raman scattering in nanoliter droplets: towards high-sensitivity detection of mercury (II) ions. Anal. Bioanal. Chem., 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.

Fiona Pereira, Stuart Hassard, John Hassard and Andrew deMello. 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, selfcoating capacity and separation efficiency. The results show complete resolution of all fragments under a range of conditions, including short separation lengths.

Jongin Hong, Hanjong Paik, Hosung Hwang, Sunghwan Lee, Andrew J. deMello and Kwangsoo No. The effect of growth temperature on physical properties of heavily doped ZnO:Al films. Phys. 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%.

Andrew J. deMello and Robert C. R. Wootton. Miniaturization: Chemistry at the crossroads. Nat. Chem., 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.

Peter M. P. Lanigan, Tanja Ninkovic, Karen Chan, Andrew J. de Mello, Keith R. Willison, David R. Klug, Richard H. Templer, Mark A. A. Neil and Oscar Ces. A microfluidic platform for probing single cell plasma membranes using optically trapped Smart Droplet Microtools (SDMs). Lab 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.

Yolanda Schaerli, Robert C. Wootton, Tom Robinson, Viktor Stein, Christopher Dunsby, Mark A. A. Neil, Paul M. W. French, Andrew J. deMello, Chris Abell and Florian Hollfelder. Continuous-Flow Polymerase Chain Reaction of Single-Copy DNA in Microfluidic Microdroplets. Anal. Chem., 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
Guillaume A. T. Chansin, Jongin Hong, Andrew J. Demello and Joshua B. Edel. Nanopore-Based Optofluidic Devices for Single Molecule Sensing. Nanofluidics: Nanoscience and Nanotechnology, 2008.

One of the primary motivations behind the development of miniaturised analysis devices has been to create new tools for modern day genomic and genetic analysis.1 At present, much effort is directed towards designing faster and more efficient DNA analysis devices that could potentially identify the genes responsible for specific diseases.2-4 One increasingly popular approach is confinement and detection of single analyte molecules within nanofluidic structures. Such devices, have at least one dimension of the channel measuring less than a few hundred nanometres.5 One of the main advantages of nanofluidics is in the ability to confine single molecules within a well defined space in order to be efficiently detected. Importantly, probing molecules at the single molecule level is essential if one wants to measure fluctuations usually lost in ensemble averaged techniques.

2008

Jongin Hong, Joshua B. Edel and Andrew J. deMello. Micro- and nanofluidic systems for high-throughput biological screening. Drug Discov. 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.

Ansgar Huebner, Dan Bratton, Graeme Whyte, Min Yang, Andrew J. deMello, Chris Abell and Florian Hollfelder. Static microdroplet arrays: a microfluidic device for droplet trapping, incubation and release for enzymatic and cell-based assays. Lab Chip, 2009, 9, 692–698

We describe the design, fabrication and use of a single-layered poly(dimethylsiloxane) microfluidic structure 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.

Fabrice Gielen, Andrew J. deMello, Tony Cass and Joshua B. Edel. Increasing the Trapping Efficiency of Particles in Microfluidic Planar Platforms by Means of Negative Dielectrophoresis. J. Phys. Chem. 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.

Xize Niu, Shelly Gulati, Joshua B. Edel and Andrew J. deMello. Pillar-induced droplet merging in microfluidic circuits. Lab 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

Ansgar Huebner, Luis F. Olguin, Daniel Bratton, Graeme Whyte, Wilhelm T. S. Huck, Andrew J. de Mello, Joshua B. Edel, Chris Abell and Florian Hollfelder. Development of Quantitative Cell-Based Enzyme Assays in Microdroplets. Anal. Chem. 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 timeresolved kinetic measurements.

Monpichar Srisa-Art, Emily C. Dyson, Andrew J. deMello and Joshua B. Edel. Monitoring of Real-Time Streptavidin-Biotin Binding Kinetics Using Droplet Microfluidics. Anal. Chem. 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 3.0e6 - 4.5e7 [1/(M.s)]

Tom Robinson, Prashant Valluri, Hugh B. Manning, Dylan M. Owen, Ian Munro, Clifford B. Talbot, Christopher Dunsby, John F. Eccleston, Geoff S. Baldwin, Mark A. A. Neil, Andrew J. de Mello and Paul M. W. French. Three-dimensional molecular mapping in a microfluidic mixing device using fluorescence lifetime imaging. Opt. Lett., 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.

Peter M.P. Lanigan, Karen Chan, Tanya Ninkovic, Richard H. Templer, P.M.W. French, A.J. deMello1,2, K. R. Willison, P.J. Parker, M.A.A. Neil, O. Ces and D.R. Klug. Spatially selective sampling of single cells using optically trapped fusogenic emulsion droplets: a new single-cell proteomic tool. J. R. Soc. 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.

Monpichar Srisa-Art, Andrew J. deMello and Joshua B. Edel. Fluorescence Lifetime Imaging of Mixing Dynamics in Continuous-Flow Microdroplet Reactors. PRL, 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.

Ansgar Huebner, Sanjiv Sharma, Monpichar Srisa-Art, Florian Hollfelder, Joshua B. Edel and Andrew J. deMello. Microdroplets: A sea of applications?. Lab 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.

Jongin Hong, Yoonjae Lee, Guillaume A T Chansin, Joshua B Edel and Andrew J deMello. 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.

Yasemin Koc, Andrew J. de Mello, G. McHale, M. I. Newton, Peter Roach and Neil J. Shirtcliffe. Nano-scale superhydrophobicity: suppression of protein adsorption and promotion of flow-induced detachment. Lab 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.

Oliver Hofmann, Donal D.C. Bradley, John C. deMello and Andrew J. deMello. Lab-on-a-Chip Devices with Organic Semiconductor-Based Optical Detection. Organic Semiconductros in Sensor Applications. Springer Series in Materials Science, 2008.

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

Monpichar Srisa-Art, Andrew J. deMello and Joshua B. Edel. High-Throughput DNA Droplet Assays Using Picoliter Reactor Volumes. Anal. Chem., 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 reac- tors to high-throughput chemistry and biology. Herein, we describe the integration of confocal fluorescence spec- troscopy as a high-efficiency detection method for droplet- based microfluidics. Issues such as surface contamina- tion, 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 com- positions 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 concentra- tions. 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.

Guillaume A. T. Chansin, Rafael Mulero, Jongin Hong, Min Jun Kim, Andrew J. deMello, and Joshua B. Edel. Single-Molecule Spectroscopy Using Nanoporous Membranes. Nano Lett., 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.

Siva Krishnadasan, Richard J. C. Brown, Andrew J. deMello and John C. deMello. Intelligent routes to the controlled synthesis of nanoparticles. Lab 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. Handbook of Capillary and Microchip Electrophoresis and Associated Microtechniques, Third Edition Edited by James P. Landers CRC Press, 2008, 1185–1204

In 1828, when attempting to prepareammoniumcyanate from silver cyanide andammoniumchloride, 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. Since that time, organic chemistry (the study of the structure, properties, composition, reactions, and synthesis of carbon-containing compounds) has flourished and is of vital importance to the pharmaceutical, chemical, cosmetic, petrochemical, and textile industries. For the vast majority of the time, since (and for centuries before) Wöhler’s synthesis of urea, the chemist’s toolkit has predominantly consisted of macroscopic components fabricated from glass. Examples of such components include round-bottomed flasks, test tubes, distillation columns, reflux condensers, Erlenmeyer flasks, drying tubes, separation funnels, recrystallization tubes, and burettes. Despite the enormous advances that have been made in experimental, mechanistic, and theoretical organic chemistry over the past 150 years it is noteworthy that the basic experimental techniques and associated laboratory equipment remain largely unaffected. Perhaps this is unsurprising, since standard laboratory glassware provides a fitting environment in which to perform the vast majority of synthetic transformations. Glass as a generic material is robust, possessing good chemical inertness. It also exhibits high thermal conductivity, low electrical conductivity, and good transparency within the visible region of the electromagnetic spectrum. This means that standard glassware can be used to process most chemical reagents under a wide range of temperatures and pressure. A more pragmatic reason for the adoption of macroscale glassware in organic synthesis relates to the fact that chemists as individuals feel comfortable performing reactions in environments, which they can easily manipulate, control, and observe. Nevertheless, although a chemist may prefer to perform a reaction within a round bottom flask, at the molecular scale it makes little difference if a reaction is processed within a volume of 100 mL or 100 pL. What is more important is that the “ideal” chemical reactor should provide an environment in which chemical state functions are precisely controllable, allowing the rapid synthesis of a desired product in high yield. To this end, over the past decade, the application of micromachining techniques cultivated within the semiconductor and microelectronics industries have allowed the creation of a new instrumental platform able to efficiently process and analyze molecular reactions on the micron to nanometer scale. This chapter aims to provide an introduction to the concept of reaction miniaturization. The theory of miniaturization is discussed and followed by a practical assessment of the use of microfluidic systems in synthetic chemistry.

Jingsong Huang, Xuhua Wang, Andrew J. deMello, John C. deMello and Donal D. C. Bradley. Efficient flexible polymer light emitting diodes with conducting polymer anodes. J. Mater. Chem., 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-dioctylfluoreneco- 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 and 8.8 cd/A 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.

Andrew J. de Mello and Joshua B. Edel. Hydrodynamic focusing in microstructures: Improved detection efficiencies in subfemtoliter probe volumes. J. Appl. Phys. 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.

Philip W. Miller, Nicholas J. Long and Andrew J. de Mello, et al. Rapid Multiphase Carbonylation Reactions by Using a Microtube Reactor: Applications in Positron Emission Tomography 11C-Radiolabeling. Angew. Chem., 2007, 119, 2933 –2936

The development of new strategies for the synthesis of positron-emitting radiolabeled compounds is of great current interest owing to the increased use of positron-emission tomography (PET) in medical imaging.

Joshua B. Edel and Andrew J. de Mello. Interphoton burst recurrence times: Single cell analysis in freely flowing solutions. Appl. Phys. Lett. 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.

Ansgar Huebner, Monpichar Srisa-Art, D. Holt, Chris Abell, Florian Hollfelder, Andrew J. deMello and Joshua B. Edel. Quantitative detection of protein expression in single cells using droplet microfluidics. Chem. Commun., 2007, 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.

Richard K. P. Benninger, Oliver Hofmann, Björn Önfelt, Ian Munro, Chris Dunsby, Daniel M. Davis, Mark A. A. Neil, Paul M. W. French and Andrew J. de Mello. Fluorescence-Lifetime Imaging of DNA–Dye Interactions within Continuous-Flow Microfluidic Systems. Angew. Chem., 2007, 119, 2278 –2281

Recent years have seen significant 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 rapid measurements on small sample volumes in areas such as chemical synthesis, DNA analysis, drug discovery, pharmaceutical screening, proteomics, and medical diagnostics. It is well recognized that, when compared to macroscale instruments, microfluidic systems engender a number of distinct advantages with respect to speed, analytical throughput, reagent usage, process control, automation, and operational and configurational flexibility. Although all these advantages are directly facilitated by system downscaling (and the associated improvements in both mass and thermal transfer), the instantaneous-reaction volumes that characterize microfluidic systems typically range from a few picoliters to hundreds of nanoliters. This means that analyte detection and identification is a significant challenge and often defines the principal limitations of a microfluidic system. Despite this problem, a variety of detection methods have been successfully transferred and integrated with microfluidic systems.

Joshua B. Edel, Pedro Lahoud, Anthony E. G. Cass and Andrew J. deMello. Discrimination between Single Escherichia coli Cells Using Time-Resolved Confocal Spectroscopy. J. Phys. Chem. 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.

Jingsong Huang, R. Xia, Y. Kim, Xuhua Wang, J. Dane, O. Hofmann, A. Mosley, Andrew J. de Mello, John C. de Mello and Donal D. C. Bradley. Patterning of organic devices by interlayer lithography. J. Mater. Chem., 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 BF, Krishnadasan S, deMello AJ, deMello JC, Shaffer MS. Accelerated synthesis of titanium oxide nanostructures using microfluidic chip. Lab 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

Maliwan Amatatongchai, Oliver Hofmann, Duangjai Nacapricha, Orawon Chailapakul and Andrew J. deMello. A microfluidic system for evaluation of antioxidant capacity based on a peroxyoxalate chemiluminescence assay. Anal. Bioanal. Chem., 2007, 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 (SAHP of 3.27× 10−3 μmol−1 L), followed by α-tocopherol (SAHP of 2.36× 10−3 μmol−1 L) and quercetin (SAHP 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.

Xuhua Wang, Oliver Hofmann, Rupa Das, Edward M. Barrett, Andrew J. deMello, John C. deMello and Donal D. C. Bradley. Integrated thin-film polymer/fullerene photodetectors for on-chip microfluidic chemiluminescence detection. Lab 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 6 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 mM, 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

Paul J. Brewer, Jingsong Huang, Paul A. Lane, Andrew J. deMello, Donal D. C. Bradley and John C. deMello. Influence of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) in polymer LEDs. Phys. Rev. B, 2006, 74, 115202

We investigate the influence of poly3,4-ethylenedioxythiophene-polystyrenesulfonate PEDOT:PSS on the optoelectronic properties of polymer light-emitting diodes containing poly9,9-dioctylfluorene PFO. Electromodulation and IV 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 electroninjecting 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.

Andrew J. deMello. 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.

David Shalom, Robert C.R. Wootton, Richard F. Winkle, Ben F. Cottam, Ramon Vilar, Andrew J. deMello and C. Paul Wilde. Synthesis of thiol functionalized gold nanoparticles using a continuous flow microfluidic reactor. Mater. Lett., 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.

Jingsong Huang, Xuhua Wang, Y. Kim, Andrew J. deMello, Donal D. C. Bradley and John C. deMello. High efficiency flexible ITO-free polymer/fullerene photodiodes. Phys. Chem. Chem. Phys., 2006, 8, 3904–3908

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

Oliver Hofmann, Xuhua Wang, Alastair Cornwell, Stephen Beecher, Amal Raja, Donal D. C. Bradley, Andrew J. deMello and John C. deMello. Monolithically integrated dye-doped PDMS long-pass filters for disposable on-chip fluorescence detection. Lab Chip, 2006, 6, 981–987

We report the fabrication of high quality monolithically integrated optical long-pass filters, for use in disposable diagnostic microchips. The filters were prepared by incorporating dye molecules directly into the microfluidic chip substrate, thereby providing a fully integrated solution that removes the usual need for discrete optical filters. In brief, lysochrome dyes were added to a poly(dimethylsiloxane) (PDMS) monomer prior to moulding of the microchip from a structured SU-8 master. Optimum results were obtained using 1 mm layers of PDMS doped with 1200 μg mL-1 Sudan II, which resulted in less than 0.01% transmittance below 500 nm (OD 4), >80% above 570 nm, and negligible autofluorescence. These spectral characteristics compare favourably with commercially available Schott-glass long-pass filters, indicating that high quality optical filters can be straightforwardly integrated into the form of PDMS microfluidic chips. The filters were found to be robust in use, showing only slight degradation after extended illumination and negligible dye leaching after prolonged exposure to aqueous solutions. The provision of low cost high quality integrated filters represents a key step towards the development of high-sensitivity disposable microfluidic devices for point-of-care diagnostics.
» Lab Chip 2006 Cover

Paul J. Brewer, Andrew J. deMello, John C. deMello, Paul A. Lane, Donal D. C. Bradley, R. Fletcher, and J. O’Brien. Influence of carrier injection on the electromodulation response of trap-rich polymer light-emitting diodes. J. Appl. Phys. 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 lower temperatures (<100 K) resemble trap-free light-emitting diodes with a uniform electric field that extends through the bulk. We consider also the effects of pixel aging and show that field redistribution effects are reduced after extended device operation.

Robert C. R. Wootton and Andrew J. deMello. A one-step protocol for the chemical derivatisation of glass microfluidic devices. Lab 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.

Richard K. P. Benninger, Yasemin Kocü, Oliver Hofmann, Jose Requejo-Isidro, Mark A. A. Neil, Paul M. W. French and Andrew J. deMello. Quantitative 3D Mapping of Fluidic Temperatures within Microchannel Networks Using Fluorescence Lifetime Imaging. Anal. Chem., 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

Philip W. Miller, Nicholas J. Long, Andrew J. de Mello, Ramon Vilar, Jan Passchier and Antony Gee. Rapid formation of amides via carbonylative coupling reactions using a microfluidic device. Chem. Commun., 2006, 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.

Richard K. P. Benninger, Oliver Hofmann, James McGinty, Jose Requejo-Isidro, Ian Munro, Mark A. A. Neil, Andrew J. deMello and Paul M. W. French. Time-resolved fluorescence imaging of solvent interactions in microfluidic devices. Opt. 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.

Oliver Hofmann, Xuhua Wang, John C. deMello, Donal D. C. Bradley and Andrew J. deMello. Towards microalbuminuria determination on a disposable diagnostic microchip with integrated fluorescence detection based on thin-film organic light emitting diodes. Lab 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)

Paul J. Brewer, Paul A. Lane, Jingsong Huang, Andrew J. deMello, Donal D. C. Bradley and John C. deMello. Role of electron injection in polyfluorene-based light emitting diodes containing PEDOT:PSS. Phys. Rev. B, 2005, 71, 205209

We report electromodulation sEMd studies of polyfluorene-based light-emitting diodes containing polys3,4- ethylene-dioxythiophened-polysstyrene-sulfonated sPEDOT:PSSd, in which the barrier to hole injection is large (~0.7 eV). 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 sSEd. The Ba devices show conventional SE behavior for low applied biases but, above turn-on, the sfieldinducedd 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.

Alexander Iles, Robin Fortt and Andrew J. de Mello. Thermal optimisation of the Reimer–Tiemann reaction using thermochromic liquid crystals on a microfluidic reactor. Lab 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 b-naphthol was performed under hydrodynamic pumping regimes.

Jingsong Huang, Paul F. Miller, Jo S. Wilson, Andrew J. de Mello, John C. de Mello and Donal D. C. Bradley. 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. Adv. Funct. Mater., 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

Shee-Ann Leung, Richard F. Winkle, Robert C. R. Wootton and Andrew J. deMello. A method for rapid reaction optimisation in continuous-flow microfluidic reactors using online Raman spectroscopic detection. 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.

Oliver Hofmann, Paul Miller, Paul Sullivan, Timothy S. Jones, John C. deMello, Donal D.C. Bradley and Andrew J. deMello. Thin-film organic photodiodes as integrated detectors for microscale chemiluminescence assays. Sens. Actuators B, 2005, 106, 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 2mm×8mm 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 ~1mM 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.

Pierre-Alain Auroux, Yasemin Koc, Andrew deMello, Andreas Manz and Philip J.R. Day. Miniaturised nucleic acid analysis. Lab 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.

Nigel P. Beard, Joshua B. Edel and Andrew J. deMello. 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.

Andrew J. de Mello, Matthew Habgood, N. Llewellyn Lancaster, Tom Welton and Robert C. R. Wootton. Precise temperature control in microfluidic devices using Joule heating of ionic liquids. Lab 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 intrachannel temperature control to within ± 0.2 degC. 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.

Siva Krishnadasan, Jordi Tovilla, Ramon Vilar, Andrew J. deMello and John C. deMello. On-line analysis of CdSe nanoparticle formation in a continuous flow chip-based microreactor. J. Mater. Chem., 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.

Paul J. Brewer, Paul A. Lane, Andrew J. deMello, Donal D. C. Bradley, J. C. deMello. Internal Field Screening in Polymer Light-Emitting Diodes. Adv. Funct. Mater. 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 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. 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.

Joshua B. Edel, Nigel P. Beard, Oliver Hofmann, John C. deMello, Donal D. C. Bradley and Andrew J. deMello. Thin-film polymer light emitting diodes as integrated excitation sources for microscale capillary electrophoresis. Lab 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 x 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 1026 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.

Robert C. R. Wootton and Andrew J. deMello. Continuous laminar evaporation: micron-scale distillation. Chem. Commun. 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

Shee-Ann Leung, Joshua B Edel, Robert C R Wootton and Andrew J deMello. Continuous real-time bubble monitoring in microchannels using refractive index detection. Meas. Sci. Technol., 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.

Joshua B. Edel and Andrew J. de Mello. Determination of single particle flow velocities in microchannels using a maximum likelihood estimator method. Phys. Chem. Chem. Phys., 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 20x, 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 4x 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.

Joshua B. Edel and Andrew J. de Mello. Single Particle Confocal Fluorescence Spectroscopy in Microchannels: Dependence of Burst Width and Burst Area Distributions on Particle Size and Flow Rate. Anal. Sci., 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.

Robin Fortt, Robert C. R. Wootton and Andrew J. de Mello. Continuous-Flow Generation of Anhydrous Diazonium Species: Monolithic Microfluidic Reactors for the Chemistry of Unstable Intermediates. OPRD, 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 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.

Andrew J. deMello. DNA amplification moves on. Nature, 2003, 422, 28-29

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

Andrew J. deMello. Microfluidics: DNA amplification moves on. Nature, 2003, 422, 28-29

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

Nigel P. Beard, Chao-Xuan Zhang and Andrew J. deMello. 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.

Andrew J. de Mello and Nigel Beard. Dealing with ‘real’ samples: sample pre-treatment in microfluidic systems. Lab Chip, 2003, 3, 11N–19N

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 Mello. Electrophoretic analysis of amines using reversed-phase, reversed-polarity, head-column field-amplified sample stacking and laser-induced fluorescence detection. J. Chromatogr. A, 2002, 979, 171–178

This paper describes the use of reversed-phase, reversed-polarity head-column field-amplified sample stacking (HCFASS) for on-line sample concentration in conventional capillary electrophoresis. The effective stacking efficiency was determined as a function of sodium hydroxide concentration in the sample matrix. Results concur with theoretical predictions where stacking efficiency depends on the conductivity (electric field strength) and electrophoretic mobility in the sample matrix solution. Fluorescein isothiocyanate-derivatized aniline and 2,4-dimethylaniline were dissolved in sodium hydroxide (800 μM), separated in a phosphate running buffer (0.05 M, pH 9.0) and detected utilising laser-induced fluorescence. The use of reversed-phase, reversed-polarity HCFASS with laser-induced fluorescence detection yielded sensitivity improvements with respect to normal injection schemes in excess of three orders of magnitude, and a limit of detection as low as 10-13 M.

Joshua B. Edel, Andrew J. deMello and John C. deMello. Solution-phase electroluminescence. Chem. Commun., 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 lightemitting diode and is distinct from the solvent-mediated electrochemical devices recently reported by Chang et al.

Shee-Ann Leung and Andrew J. de Mello. On-column pre-concentration of alcohol dehydrogenase in capillary electrophoresis. J. Sep. Sci. 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 5e-13 M. Both qualitative and quantitative aspects of this method are investigated.

Nigel P. Beard and Andrew J. de Mello. 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 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.

Joshua B. Edel, Robin Fortt, John C. deMello and Andrew J. deMello. Microfluidic routes to the controlled production of nanoparticles. Chem. Commun., 2002, 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 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 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.

Andrew de Mello and Robert Wootton. But what is it good for? Applications of microreactor technology for the fine chemical industry. Lab 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.

Andrew de Mello. Plastic fantastic?. Lab 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.

Robert C. R. Wootton, Robin Fortt and Andrew J. de Mello. A Microfabricated Nanoreactor for Safe, Continuous Generation and Use of Singlet Oxygen. OPRD, 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.

Robert C. R. Wootton, Robin Fortt and Andrew J. de Mello. On-chip generation and reaction of unstable intermediates—monolithic nanoreactors for diazonium chemistry: Azo dyes. Lab 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

Andrew J. de Mello. DNA amplification: does ‘small’ really mean ‘efficient’?. Lab 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.

Andrew J. de Mello. Miniaturization. Anal. Bioanal. Chem., 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.

V. Nittis, Robert Fortt, C. H. Legge and Andrew J. de Mello. A high-pressure interconnect for chemical microsystem applications. Lab 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.

Stephen C. Jakeway and Andrew J. de Mello. 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.

Michael C. Mitchell, Valerie Spikmans, Andreas Manz and Andrew J. de Mello. Microchip-based synthesis and total analysis systems (μSYNTAS): chemical microprocessing for generation and analysis of compound libraries. J. Chem. Soc., Perkin Trans., 2001, 1, 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.

Somsak Sirichai and Andrew J. de Mello. 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, 348-54

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
Andrew J. de Mello. Chip-MS: Coupling the large with the small. Lab 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

Michael C. Mitchell, Valerie Spikmans and Andrew J. de Mello. Microchip-based synthesis and analysis: Control of multicomponent reaction products and intermediates. Analyst, 2001, 126, 24–27

A miniaturised-SYNthesis and Total Analysis System (μSYNTAS) was used for the solution-phase synthesis and on-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 and 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.

Elisabeth K. Hill and Andrew J. de Mello. Single-molecule detection using confocal fluorescence detection: Assessment of optical probe volumes. 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.

Stephen C. Jakeway, Andrew J. de Mello and Emma L. Russell. Miniaturized total analysis systems for biological analysis. Fresenius J. Anal. Chem., 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.

Somsak Sirichai and Andrew J. de Mello. A capillary electrophoresis microchip for the analysis of photographic developer solutions using indirect fluorescence detection. 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

Fiona G. Bessoth, Andrew J. deMello and Andreas Manz. Microstructure for efficient continuous flow mixing. Anal. Commun., 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.

Andrew J. de Mello, Andreas Manz. Chip technology for micro-separation. Microsystem Technology - A Powerful Tool for Biomolecular Studies. Editors: Saluz, Hans-Peter, Köhler, M., Mejevaia, T. (Eds.), ISBN: 978-3034888172

1998

Christopher D. Byrne, Andrew J. de Mello and William L. Barnes. Variable-Angle Time-Resolved Evanescent Wave-Induced Fluorescence Spectroscopy (VATR-EWIFS): A Technique for Concentration Profiling Fluorophores at Dielectric Interfaces. J. Phys. Chem. 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 fluorescence spectroscopy is used to measure the variations in the fluorescence quantum yield caused by the pressence 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.

Elisabeth K. Hill, Andrew J. de Mello, Helen Birrell, Joanne Charlwood and Patrick Camilleri. Steady state and time-resolved fluorescence of 2-aminoacridone sugar derivatives. J. Chem. Soc., Perkin Trans. 2, 1998, 11, 2337–2341

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.

Norbert Burggraf, Beat Krattiger, Andrew J. de Mello, Nico F. de Rooij and Andreas Manz. Holographic refractive index detector for application in microchip-based separation systems. 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.

Christopher D. Byrne and Andrew J. de Mello. Photophysics of ethidium bromide complexed to ct-DNA: a maximum entropy study. Biophys. Chem., 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.

Martin U. Kopp, Andrew J. de Mello and Andreas Manz. Chemical Amplification: Continuous-Flow PCR on a Chip. Science, 1998, 280, 1046-1048

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

1997

Arun Arora, Andrew J. de Mello and Andreas Manz. Sub-microliter Electrochemiluminescence Detector—A Model for Small Volume Analysis Systems. Anal. Commun., 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

Adam T. Woolley, Dean Hadley, Phoebe Landre, Andrew J. deMello, Richard A. Mathies and M. Allen Northrup. Functional Integration of PCR Amplification and\r\nCapillary Electrophoresis in a Microfabricated DNA\r\nAnalysis Device. Anal. Chem., 1996, 68, 4081-4086

Microfabricated silicon PCR reactors and glass capillary\r\nelectrophoresis (CE) chips have been successfully coupled\r\nto form an integrated DNA analysis system. This con-\r\nstruct combines the rapid thermal cycling capabilities of\r\nmicrofabricated PCR devices (10 °C/s heating, 2.5 °C/s\r\ncooling) with the high-speed (<120 s) DNA separations\r\nprovided by microfabricated CE chips. The PCR chamber\r\nand the CE chip were directly linked through a photo-\r\nlithographically fabricated channel filled with hydroxyeth-\r\nylcellulose sieving matrix. Electrophoretic injection di-\r\nrectly from the PCR chamber through the cross injection\r\nchannel was used as an “electrophoretic valve” to couple\r\nthe PCR and CE devices on-chip. To demonstrate the\r\nfunctionality of this system, a 15 min PCR amplification\r\nof a -globin target cloned in M13 was immediately\r\nfollowed by high-speed CE chip separation in under 120\r\ns, providing a rapid PCR-CE analysis in under 20 min.\r\nA rapid assay for genomic Salmonella DNA was per-\r\nformed in under 45 min, demonstrating that challenging\r\namplifications of diagnostically interesting targets can also\r\nbe performed. Real-time monitoring of PCR target am-\r\nplification in these integrated PCR-CE devices is also\r\nfeasible. Amplification of the -globin target as a function\r\nof cycle number was directly monitored for two different\r\nreactions starting with 4 × 107 and 4 × 105 copies of DNA\r\ntemplate. This work establishes the feasibility of perform-\r\ning high-speed DNA analyses in microfabricated inte-\r\ngrated fluidic systems.

Andrew J. deMello, Julia A. Elliott and Garry Rumbles. Evanescent wave-induced fluorescence study of Rhodamine 101 at dielectric interfaces. J. Chem. SOC., Faraday Trans., 1997, 93, 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.

Andrew J. de Mello. Total Internal Reflection Fluorescence Spectroscopy. Davies, John. Surface analytical techniques for probing biomaterial processes. CRC press, 1996., ISBN: 978-0849383526
Garry Rumbles, I.D.W. Samuel, L. Magnani, K.A. Murray, A.J. DeMello, B. Crystall, S.C. Moratti, B.M. Stone, A.B. Holmes, R.H. Friend. Chromism and luminescence in regioregular poly(3-dodecylthiophene). Synthetic Met., 1996, 76, 47-51

We report photoluminescence studies of poly( 3-dodecylthiophene) (P3DT) in solution. In a good solvent the polymer exhibits luminescence\r\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\r\nquantum efficiency and a decay profile that is non-monoexponential, but has an average lifetime that is very similar to the good solvent\r\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\r\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\r\nthe thin film, suggesting that the polymer aggregates in the solution and the emitting species is the same in both environments. The data are\r\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

S. Dhami, Andrew J. De Mello, Garry Rumbles, S. M. Bishop D. Phillips and A. Beeby. Phthalocyanine fluorescence at high concentration Dimers or reabsorption effect?. Photochem. Photobiol., 1995, 61, 341-346

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

Andrew J. deMello, B. Crystall and Garry Rumbles. Evanescent-Wave Spectroscopic Studies of Surface-Enhanced Fluorescence \r\nQuantum Efficiencies. J. Coll. Inter. Sci., 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