Search

Optoelectronic tweezers (OET) is a noncontact micromanipulation technology for controlling microparticles and cells. In the OET, it is necessary to configure a medium with different electrical properties to manipulate different particles and to avoid the interaction between two particles. Here, a new method exploiting the interaction between different dielectric properties of micro-objects to achieve the trapping, transport, and release of particles in the OET system was proposed. Besides, the effect of interaction between the micro-objects with positive and negative dielectric properties was simulated by the arbitrary Lagrangian-Eulerian (ALE) method. In addition, compared with conventional OET systems relying on fabrication processes involving the assembly of photoelectric materials, a contactless OET platform with an iPad-based wireless-control interface was established to achieve convenient control. Finally, this platform was used in the interaction of swimming microorganisms (positive-dielectric properties) with microparticles (negative-dielectric properties) at different scales. It showed that one particle could interact with 5 particles simultaneously, indicating that the interaction can be applied to enhance the high-throughput transportation capacities of the OET system and assemble some special microstructures. Owing to the low power, microorganisms were free from adverse influence during the experiment. In the future, the interaction of particles in a simple OET platform is a promising alternative in micro-nano manipulation for controlling drug release from uncontaminated cells in targeted therapy research.

Finger-stick blood sampling is convenient for point of care diagnostics, but whole blood samples are problematic for many assays because of severe matrix effects associated with blood cells and cell debris. We introduce a new digital microfluidic (DMF) diagnostic platform with integrated porous membranes for blood-plasma separation from finger-stick blood volumes, capable of performing complex, multi-step, diagnostic assays. Importantly, the samples can be directly loaded onto the device by a finger "dab" for user-friendly operation. We characterize the platform by comparison to plasma generated via the "gold standard" centrifugation technique, and demonstrate a 21-step rubella virus (RV) IgG immunoassay yielding a detection limit of 1.9 IU mL-1, below the diagnostic cut-off. We propose that this work represents a critical next step in DMF based portable diagnostic assays-allowing the analysis of whole blood samples without pre-processing.

Micromanipulation techniques that are capable of assembling nano/micromaterials into usable structures such as topographical micropatterns (TMPs) have proliferated rapidly in recent years, holding great promise in building artificial electronic and photonic microstructures. Here, a method is reported for forming TMPs based on optoelectronic tweezers in either "bottom-up" or "top-down" modes, combined with in situ photopolymerization to form permanent structures. This work demonstrates that the assembled/cured TMPs can be harvested and transferred to alternate substrates, and illustrates that how permanent conductive traces and capacitive circuits can be formed, paving the way toward applications in microelectronics. The integrated, optical assembly/preservation method described here is accessible, versatile, and applicable for a wide range of materials and structures, suggesting utility for myriad microassembly and microfabrication applications in the future.

Microcoil nuclear magnetic resonance (NMR) has been interfaced with digital microfluidics (DMF) and is applied to monitor organic reactions in organic solvents as a proof of concept. DMF permits droplets to be moved and mixed inside the NMR spectrometer to initiate reactions while using sub-microliter volumes of reagent, opening up the potential to follow the reactions of scarce or expensive reagents. By setting up the spectrometer shims on a reagent droplet, data acquisition can be started immediately upon droplet mixing and is only limited by the rate at which NMR data can be collected, allowing the monitoring of fast reactions. Here we report a cyclohexene carbonate hydrolysis in dimethylformamide and a Knoevenagel condensation in methanol/water. This is to our knowledge the first time rapid organic reactions in organic solvents have been monitored by high field DMF-NMR. The study represents a key first step towards larger DMF-NMR arrays that could in future serve as discovery platforms, where computer controlled DMF automates mixing/titration of chemical libraries and NMR is used to study the structures formed and kinetics in real time.

Optoelectronic tweezer (OET) is a useful optical micromanipulation technology that has been demonstrated for various applications in electrical engineering and most notably cell selection for biomedical engineering. In this work, we studied the use of light patterns with different shapes and thicknesses to manipulate dielectric microparticles with OET. It was demonstrated that the maximum velocities of the microparticles increase to a peak and then gradually decrease as the light pattern’s thickness increases. Numerical simulations were run to clarify the underlying physical mechanisms, and it was found that the observed phenomenon is due to the co-influence of horizontal and vertical dielectrophoresis forces related to the light pattern’s thickness. Further experiments were run on light patterns with different shapes and objects with different sizes and structures. The experimental results indicate that the physical mechanism elucidated in this research is an important one that applies to different light pattern shapes and different objects, which is useful for enabling users to optimize OET settings for future micromanipulation applications.

Microfluidic sample manipulation is a key enabler in modern chemical biology research. Both discrete droplet-based digital microfluidic (DMF) assays and continuous flow in-channel assays are well established, each featuring unique advantages from the viewpoint of automation and parallelization. However, there are marked differences in the applicable microfabrication materials and methods, which limit the interfacing of DMF sample preparation with in-channel separation systems, such as the gold standard microchip electrophoresis. Simultaneously, there is an increasing demand for low-cost and user-friendly manufacturing techniques to foster the adaptation of microfluidic technology in routine laboratory analyses. This work demonstrates integration of DMF with in-channel separation systems using only low-cost and accessible (non-cleanroom) manufacturing techniques, i.e., inkjet printing of silver for patterning of the driving electrodes and UV curing of off-stoichiometric thiol-ene (OSTE) polymers both for dielectric coating of the electrode arrays and replica molding of the microchannel network. As a dielectric, OSTE performs similar to Parylene C (a gold standard dielectric in electrowetting), whereas its tunable surface and bulk properties facilitate straightforward bonding of the microchannel with the dielectric layer. In addition, a new chip design that facilitates efficient droplet transfer from the DMF part to the microchannel inlet solely by electrowetting is showcased.

The rectification of ion transport through biological ion channels has attracted much attention and inspired the thriving invention and applications of ionic diodes. However, the development of high-performance ionic diodes is still challenging, and the working mechanisms of ionic diodes constructed by 1D ionic nanochannels have not been fully understood. This work reports the systematic investigation of the design and mechanism of a new type of ionic diode constructed from horizontally aligned multi-walled carbon nanotubes (MWCNTs) with oppositely charged polyelectrolytes decorated at their two entrances. The major design and working parameters of the MWCNT-based ionic diode, including the ion channel size, the driven voltage, the properties of working fluids, and the quantity and length of charge modification, are extensively investigated through numerical simulations and/or experiments. An optimized ionic current rectification (ICR) ratio of 1481.5 is experimentally achieved on the MWCNT-based ionic diode. These results promise potential applications of the MWCNT-based ionic diode in biosensing and biocomputing. As a proof-of-concept, DNA detection and HIV-1 diagnosis is demonstrated on the ionic diode. This work provides a comprehensive understanding of the working principle of the MWCNT-based ionic diodes and will allow rational device design and optimization.

In digital microfluidics, discrete droplets of fluid are made to move on an open surface with no microchannels. These systems are commonly operated by application of electrical driving forces to an array of electrodes. While these driving forces are well characterized, the dissipative forces opposing droplet movement have not been as thoroughly examined. In recognition of this deficit, we used force-velocity plots to characterize droplet movement in digital microfluidics, which was found to be consistent with a simple theoretical framework for understanding dissipation effects for droplets in two-plate, air-filled devices. Interestingly, in some conditions, a previously unreported ″velocity saturation″ effect was observed. When examined across a range of different liquids, the forces at which this saturation occurs seem to be lower for liquids with smaller surface tensions. Furthermore, when driven at forces that cause saturation, physical phenomena are observed that are akin to what has been reported for stationary droplets in the electrowetting literature. These phenomena are detrimental to device performance, leading to a new "force window" approach that delineates the optimum operation conditions for different liquids. We propose that these findings may be useful for a wide range of applications for experts and new users alike in this growing field.

In this work, we introduce a new type of optical micromanipulation platform that we call patterned optoelectronic tweezers (p-OET). In p-OET devices, the photoconductive layer (that is contiguous in a conventional OET device) is patterned, forming regions in which the electrode layer is locally exposed. We demonstrate that the micro-patterns in the photoconductive layer are useful for repelling unwanted particles/cells, and also for keeping selected particles/cells in place after turning off the light source. We propose that the new technique may be useful for myriad applications in the rapidly growing area of optical micromanipulation.

Controlled ion transport through ion channels of cell membranes regulates signal transduction processes in biological systems and has also inspired the thriving development of ionic electronics (ionotronics or iontronics) and biocomputing. However, for constructing highly integrated ionic electronic circuits, the integration of natural membrane‐spanning ion channel proteins or artificial nanomembrane‐based ionic diodes into planar chips is still challenging due to the vertically arranged architecture of conventional nanomembrane‐based artificial ionic diodes. Here, a new design of ionic diode is reported, which allows chip‐scale integration of ionotronics, based on horizontally aligned nanochannels made from multiwalled carbon nanotubes (MWCNTs). The rectification of ion transport through the MWCNT nanochannels is enabled by decoration of oppositely charged polyelectrolytes on the channel entrances. Advanced ionic electronic circuits including ionic logic gates, ionic current rectifiers, and ionic bipolar junction transistors (IBJT) are demonstrated on planar nanofluidic chips by stacking a series of ionic diodes fabricated from the same bundles of MWCNTs. The horizontal arrangement and facile chip‐scale fabrication of the MWCNT ionic diodes may enable new designs of complex but monolithic ionotronic systems. The MWCNT ionic diode may also prove to be an excellent platform for investigation of electrokinetic ion transport in 1D carbon materials.

We present a novel method for in-plane digital microfluidic spectroscopy. In this technique, a custom manifold (.stl file available online as ESM) aligns optical fibres with a digital microfluidic device, allowing optical measurements to be made in the plane of the device. Because of the greater width vs thickness of a droplet on-device, the in-plane alignment of this technique allows it to outperform the sensitivity of vertical absorbance measurements on digital microfluidic (DMF) devices by ∼14×. The new system also has greater calibration sensitivity for thymol blue measurements than the popular NanoDrop system by ∼2.5×. The improvements in absorbance sensitivity result from increased path length, as well as from additional effects likely caused by liquid lensing, in which the presence of a water droplet between optical fibres increases fibre-to-fibre transmission of light by ∼2× through refraction and internal reflection. For interrogation of dilute samples, stretching of droplets using digital microfluidic electrodes and adjustment of fibre-to-fibre gap width allows absorbance path length to be changed on-demand. We anticipate this new digital microfluidic optical fibre absorbance and fluorescence measurement system will be useful for a wide variety of analytical applications involving microvolume samples with digital microfluidics.

Nanostructured microelectrodes (NMEs) are three-dimensional electrodes that have superb sensitivity for electroanalysis. Here we report the integration of NMEs with the versatile fluid-handling system digital microfluidics (DMF), for eventual application to distributed diagnostics outside of the laboratory. In the new methods reported here, indium tin oxide DMF top plates were modified to include Au NMEs as well as counter and pseudoreference electrodes. The new system was observed to outperform planar sensing electrodes of the type that are typically integrated with DMF. A rubella virus (RV) IgG immunoassay was developed to evaluate the diagnostic potential for the new system, relying on magnetic microparticles coated with RV particles and analysis by differential pulse voltammetry. The limit of detection of the assay (0.07 IU mL(-1)) was100× below the World Health Organization defined cut-off for rubella immunity. The sensitivity of the integrated device and its small size suggest future utility for distributed diagnostics.

Non-specific adsorption of biomolecules (or “biofouling”) is a major problem in microfluidics and many other applications. The problem is particularly pernicious in digital microfluidics (DMF, a technique in which droplets are manipulated electrodynamically on an array of electrodes coated with a hydrophobic insulator), as local increases in surface energy that arise from fouling can cause droplet movement to fail. We report a new solution to this problem: a device coating bearing a combination of fluorinated poly(ethylene glycol) functionalities (FPEG) and perfluorinated methacrylate (FA) moieties. A range of different FPEG-FA copolymers were synthesized containing varying amounts of FPEG relative to the fluorinated backbone. Coatings with low%FPEG were found to result in significant reductions in protein adsorption and improvements in device lifetime (up to 5.5-fold) relative to the state of the art. An analysis of surface topology and chemistry suggests that FPEG-FA surfaces undergo a dynamic reconstruction upon activation by applying DMF driving potentials, with FPEG groups forming vertical protrusions out of the plane of the device surface. An analysis of changes in surface wettability and adhesion as a function of activation supports this hypothesis. This innovation represents an advance for digital microfluidics, and may also find use in other applications that are currently limited by biofouling.

A microfluidic technique for combinatorial chemical synthesis of peptidomimetics has been developed. The new method is fast, automated and includes an integrated magnetic separation of inorganic catalysts from reaction products. This proof-of-concept study should lead to methods for generating libraries of compounds suitable for screening for bioactivity.

Optical micromanipulation has become popular for a wide range of applications. In this work, a new type of optical micromanipulation platform, patterned optoelectronic tweezers (p-OET), is introduced. In p-OET devices, the photoconductive layer (that is continuous in a conventional OET device) is patterned, forming regions in which the electrode layer is locally exposed. It is demonstrated that micropatterns in the photoconductive layer are useful for repelling unwanted particles/cells, and also for keeping selected particles/cells in place after turning off the light source, minimizing light-induced heating. To clarify the physical mechanism behind these effects, systematic simulations are carried out, which indicate the existence of strong nonuniform electric fields at the boundary of micropatterns. The simulations are consistent with experimental observations, which are explored for a wide variety of geometries and conditions. It is proposed that the new technique may be useful for myriad applications in the rapidly growing area of optical micromanipulation.

made with high chemoselectivity from amino acids or linear peptides, isocyanides, and amphoteric aziridine aldehydes in a one-step process. Importantly, the resulting products possess useful structural features that allow specific modification at defined positions. In our initial work, we formed serial batches of peptides using conventional macroscale synthetic techniques. The utility of this method is limited, however, without a high-throughput approach for generating focused libraries of peptide macrocycles. Such a method would be automated and would enable multistep reactions to be handled in parallel. Herein, we present a new miniaturized technique for synchronized on-chip synthesis of peptide macrocycles and related products. The most common format for miniaturized synthesis is enclosed microchannels in planar platforms. Such systems have been used for conventional organic synthesis, polymerization reactions, formation of biomolecules, such as peptides and DNA, and generation of nanoparticles and colloids. However, there are some challenges that limit the scope of their use for parallel chemical synthesis. For example, many microchannel platforms are formed from poly(dimethylsiloxane), a material that is susceptible to degradation in common organic solvents. Furthermore, control of many reagents simultaneously (a feature required to implement parallel synthetic reactions) in microchannels requires pumps, tubing, valves, and/or threedimensional channel networks that can be difficult to fabricate and operate. This has prompted researchers to develop specialized techniques to overcome this limitation. Another disadvantage associated with the microchannel format is the challenge inherent in the removal of solvents and re-dissolution of solids that are common steps in synthesis. Solid reagents and products can clog microchannels, making targeted reagent delivery difficult to control. Finally, the small volumes of samples in microchannels makes it difficult to recover them in sufficient quantities for off-line analysis techniques, such as NMR spectroscopy. In need of a platform capable of generating a) peptide macrocycles for downstream transfer onto functionalized surfaces, and b) spatially resolved macrocyclic peptide products in the solid state, we chose an alternative format for automation of synthesis, called digital microfluidics. In digital microfluidics, discrete nL to mL sized droplets of samples and reagents are controlled in parallel by applying a series of electrical potentials to an array of electrodes coated with a hydrophobic insulator (Figure 1). Digital microfluidics has become popular for biological and chemical applications, including cell culture and assays, enzyme assays, immunoassays, protein processing, clinical sample processing and analysis, and synthesis of anisotropic Scheme 1. Synthesis of peptide-based macrocycles and their structurally modified derivatives.

We present a straightforward, accessible method to covalently pattern proteins in poly(dimethyl siloxane) (PDMS) microchannels. Our approach includes (i) region-specific photografting of a layer of poly(acrylamide) (PAAm) and (ii) bioconjugation of PAAm with a desired protein. The method produces symmetric protein patterns on all channel walls, which have high specificity and pattern fidelity, are compatible with a variety of geometries and exhibit excellent longevity under shear stresses of up to 1 dyn/cm. We demonstrate the generality of the method by creating multi-protein gradients within microfluidic microchannels and by in-situ patterning of islands of multiple proteins. Protein activity was observed by the digestion of BODIPY-casein using channels patterned with trypsin.

We investigated the flow dynamics of biotin-conjugated microgel capsules in avidin-conjugated microchannel constrictions. Microgels were prepared using a microfluidic assembly approach. Biotinylated microgels passing through avidin-modified constrictions slowed relative to several control systems. This effect was observed below a critical velocity of the microgels in the channel-at-large. The reduction in microgel velocity in the constriction occurred for several different sizes of microgels and orifices. Soft compliant microgels showed a lower velocity in the constriction relative to rigid microgels with the same concentration of biotin on the surface, due to the ability of the softer microgels to deform in the orifice and maximize their surface area when in contact with the orifice wall.

An innovative and simple microfabrication method for digital microfluidics is presented. In this method, devices are formed from copper substrates or gold compact disks using rapid marker masking to replace photolithography. The new method is capable of forming devices with inter-electrode gaps as small as 50 μm. Saran™ wrap (polyethylene film) and commercial water repellants were used as dielectric and hydrophobic coatings, respectively, to replace commonly used and more expensive materials such as parylene-C and Teflon-AF. Devices formed by the new method enabled single- and two-plate actuation of droplets with volumes of 1–12 μL. Fabricated devices were successfully tested for droplet manipulation, merging and splitting. We anticipate that this fabrication method will bring digital microfluidics within the reach of any laboratory with minimal facilities.

is a barrier to its growth and development. Conse-quently, DMF devices are limited to use in a few laboratoriesworldwide.The availability of an accessible microfabrication techniqueis critical for the growth and continued development of DMF.An analogy can be made to the state of conventional, chan-nel-based microfluidics in the mid-1990s. A database searchreveals that approximately eight articles per year were pub-lished on the subject of channel microfluidics in 1992–1998;this number exploded to approximately 53 articles per yearin 1999–2000.

An integrated microfluidic device has been fabricated for analyzing the chemical contents of a single cell (chemical cytometry). The device is designed to accomplish four different functions: ( i ) cell handling, ( ii ) metering and delivering of chemical reagents, ( iii ) cell lysis and chemical derivatization, and ( iv ) separating derivatized compounds and detecting them by laser-induced fluorescence. These functions are accomplished with only two valves, formed by multilayer soft lithography. A new kind of three-state valve and a picopipette are described; these elements are crucial for minimizing the reaction volume and ensuring optimal shape of the channel for electrophoresis injection. By using these valves, a reaction volume of ≈70 pl is achieved for the lysis and derivitization of the contents of a single Jurkat T cell (≈10 μm diameter). As a demonstration of the use of this integrated microfluidic device, electropherograms of amino acids from individual Jurkat T cells are recorded and compared with those collected from a multiple-cell homogenate.

Poly(dimethylsiloxane) (PDMS) microfluidic devices were prepared from different ratios of "curing agent" (which contains silicon hydride groups) to "base" (which contains vinyl-terminated noncross-linked PDMS), to determine the effect of this ratio on electroosmotic flow (EOF). In fabricating devices for this purpose, a novel method for permanently enclosing PDMS channels was developed. As a supplement to the microfluidic method, the inner walls of capillaries were coated with PDMS formed from varying ratios of curing agent to base. EOF was found to be constant for PDMS formed with each ratio, which implies that the negative surface charges do not arise from chemical species present only in the base or the curing agent.

We report the fabrication of a scaffold (hereafter referred to as AngioChip) that supports the assembly of parenchymal cells on a mechanically tunable matrix surrounding a perfusable, branched, three-dimensional microchannel network coated with endothelial cells. The design of AngioChip decouples the material choices for the engineered vessel network and for cell seeding in the parenchyma, enabling extensive remodelling while maintaining an open-vessel lumen. The incorporation of nanopores and micro-holes in the vessel walls enhances permeability, and permits intercellular crosstalk and extravasation of monocytes and endothelial cells on biomolecular stimulation. We also show that vascularized hepatic tissues and cardiac tissues engineered by using AngioChips process clinically relevant drugs delivered through the vasculature, and that millimetre-thick cardiac tissues can be engineered in a scalable manner. Moreover, we demonstrate that AngioChip cardiac tissues implanted with direct surgical anastomosis to the femoral vessels of rat hindlimbs establish immediate blood perfusion.

Three-dimensional (3D) hydrogel structures are finding use in fundamental studies of self-assembly, rheology, and 3D cell culture. Most techniques for 3D hydrogel formation are 'single pot', in which gels are not addressable after formation. For many applications, it would be useful to be able to form arrays of gels bearing mixtures of constituents and/or formed from composites of different gel materials. Here, in response to this challenge, we introduce a digital microfluidic method for 'on-demand' formation of arrays of microgels bearing arbitrary contents and shapes. On formation of the gels, each microgel is individually addressable for reagent delivery and analysis. We demonstrate the utility of the method for 3D cell culture and higher-order tissue formation by implementing the first sub-microlitre recapitulation of 3D kidney epithelialization. We anticipate this platform will enable new research that can exploit the flexible nature of this technique for forming and addressing arrays of hydrogels with unique geometries and contents.

The first example of so-called "digital microfluidics" (DMF) implemented on paper by inkjet printing is reported. A sandwich enzyme-linked immunosorbent assay (ELISA) is demonstrated as an example of a complex, multistep protocol that would be difficult to achieve with capillary-driven paper microfluidics. Furthermore, it is shown that paper-based DMF devices have comparable performance to traditional photolithographically patterned DMF devices at a fraction of the cost.

Three-dimensional hydrogel based cell culture has increased in prominence as a function of the in vivo-like phenotypes observed for cells cultured in this way. Unfortunately, cost and challenges in the physical manipulation of delicate hydrogel materials has impeded widespread use of these methods. Here we report the first digital microfluidic platform for the on-demand formation of hydrogel structures in virtual microwells. Moreover, we use the device to automate seeding of cells in hydrogels, exchange media at regular intervals, and perform fixing and staining of cells for on-device light and confocal microscopy. Further we apply this method for the recapitulation of higher-order tissue formation in a model of kidney epithelialization. These findings demonstrate the potential of digital microfluidics as a useful tool for a broad range of hydrogel based technologies.

Digital microfluidic devices allow the manipulation of droplets between two parallel electrodes. These electrodes can act as mirrors generating a micro-cavity, which can be exploited for a droplet dye-laser. Three representative laser-dyes with emission wavelengths spanning the whole visible spectrum are chosen to show the applicability of this concept. Sub-microlitre droplets of laser-dye solution are moved in and out of a lasing site on-chip to down-convert the UV-excitation light into blue, green and red laser-pulses.

Biofouling in microfluidic devices limits the type of samples which can be handled and the duration for which samples can be manipulated. Despite the cost of disposing fouled devices, relatively few strategies have been developed to tackle this problem. Here, we have analyzed a series of eight amphiphilic droplet additives, Pluronic coblock polymers of poly(propylene oxide) (PPO) and poly(ethylene oxide) (PEO), as a solution to biofouling in digital microfluidics using serum-containing cell culture media as a model fluid. Our analysis shows that species with longer PPO chains are superior for enabling droplet motion and reducing biofouling. Two of the tested species, L92 and P105, were found to lengthen device lifetimes by 2-3 times relative to additives used previously when used at optimal concentrations. Pluronics with low PEO content such as L92 were found to be cytotoxic to an immortalized mammalian cell line, and therefore we recommend that Pluronic additives with greater or equal to 50% PEO composition, such as P105, be used for digital microfluidic applications involving cells. Finally, contact angle measurements were used to probe the interaction between Pluronic-containing droplets and device surfaces. Strong correlations were found between various types of contact angle measurements and the capacity of additives to reduce biofouling, which suggests that contact angle measurements may be useful as a tool for rapidly screening new candidates for the potential to reduce biofouling. We propose that this study will be useful for scientists and engineers who are developing digital microfluidic platforms for a wide range of applications involving protein-containing solutions, and in particular, for applications involving cells. � 2011 American Chemical Society.

Since the inception of soft lithography, microfluidic devices for cardiovascular research have been fabricated easily and cost-effectively using the soft lithography method. The drawback of this method was the fabrication of microchannels with rectangular cross-sections, which did not replicate the circular cross-sections of blood vessels. This article presents a novel, straightforward approach for the fabrication of microchannels with circular cross-sections in poly(dimethylsiloxane) (PDMS), using soft lithography. The method exploits the polymerization of the liquid silicone oligomer around a gas stream when both of them are coaxially introduced in the microchannel with a rectangular cross-section. We demonstrate (i) the ability to control the diameter of circular cross-sections of microchannels from ca. 40-100 mum; (ii) the fabrication of microchannels with constrictions, and (iii) the capability to grow endothelial cells on the inner surface of the microchannels.

We investigated the flow dynamics of microgel capsules in topographically patterned microfluidic devices. For microgels flowing through channel constrictions, or orifices, we observed three phenomena: (i) the effect of confinement, (ii) the role of interactions between the microgels and the channel surface, and (iii) the effect of the velocities of microgels prior to their passage through an orifice. We studied negatively charged alginate microgels and positively charged alginate microgels coated with N-(2-hydroxy)propyl-3-trimethylammonium chitosan chloride (HTCC). Aqueous dispersions of microgels were driven through poly(dimethyl siloxane) microchannels carrying a weak negative surface charge. The velocity of the continuous phase, and hence, the velocity of the microgels increased as they passed through topographically patterned orifices. Alginate microgels were observed to have a larger increase in velocity relative to HTCC-coated alginate microgels. This effect, which was attributed to electrostatic attraction or repulsion, was found to be strongest for orifices with dimensions close to the microgel diameter. For example, when 75 microm-diameter microgels flowed through a 76 microm orifice, alginate gels (negatively charged) experienced a 2x greater increase in velocity than HTCC-coated (positively charged) microgels. This effect was exaggerated at lower initial flow rates. For example, when 75 microm-diameter microgels flowed through an 80 microm orifice, a two-fold difference in the velocity changes of the two microgel types was observed when the initial flow rate was 275 microm s(-1), while a three-fold difference in velocity changes was observed when the initial flow rate was 130 microm s(-1). We speculate that these studies will be useful for modeling the flow of suspensions of cells or other biologically relevant particles for a wide range of applications.

We introduce a method for 3D droplet actuation in digital microfluidics, which we have called all terrain droplet actuation (ATDA), in which droplets are manipulated on inclined, declined, vertical, twisted and upside down architectures. ATDA enables discrete processes on a single platform without thermal, chemical, or biological interference between them. To illustrate this capacity, we developed sensors capable of cycling droplets between distinct temperatures and oxygen milieu. We anticipate that ATDA will have significant impact in the field of microfluidics and the growing trend toward laboratory miniaturization.

To realize multiplexed sample preparation on a digital microfluidic chip for high-throughput Matrix Assisted Laser Desorption/Ionization Mass Spectrometry (MALDI-MS), several fluidic functions need to be integrated. These include the generation of multiple droplets from a reservoir and parallel in-line sample purification. In this paper, we develop two critical new functions in handling protein solutions and standard proteomic reagents with electrowetting-on-dielectric (EWOD) actuation, leading to an integrated chip for multiplexed sample preparation for MALDI-MS. The first is a voltage sequence designed to generate a series of droplets from each of the three reservoirs--proteomic sample, rinsing fluid, and MALDI reagents. It is the first time that proteomic reagents have been dispensed using EWOD in an air (as opposed to oil) environment. The second is a box-in-box electrode pattern developed to allow droplet passing over dried sample spots, making the process of in-line sample purification robust for parallel processing. As a result, parallel processing of multiple sample droplets is demonstrated on the integrated EWOD-MALDI-MS chip, an important step towards high-throughput MALDI-MS. The MS results, collected directly from the integrated devices, are of good quality, suggesting that the tedious process of sample preparation can be automated on-chip for MALDI-MS applications as well as other high-throughput proteomics applications.

We present a novel sample preparation technique using electrowetting-based digital microfluidics for matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS). We demonstrate that critical functions, such as generation of droplets from reservoirs and sample purification can be achieved for standard MALDI-MS reagents and analytes by electrowetting-on-dielectric (EWOD) actuation. The results, collected using devices with droplets suspended in air (rather than oil (Pollack et al., 2000)), suggest that the tedious process of sample preparation can be automated on-chip for high-throughput proteomics and other applications of MALDI-MS.

Spatial patterning of thin polyacrylamide films bonded to self-assembled monolayers on silica microchannels is described as a means for manipulating cell-adhesion and electroosmotic properties in microchips. Streaming potential measurements indicate that the zeta potential is reduced by at least two orders of magnitude at biological pH, and the adhesion of several kinds of cells is reduced by 80–100%. Results are shown for cover slides and in wet-etched silica microchannels. Because the polyacrylamide film is thin and transparent, this film is consistent with optical manipulation of cells and detection of cell contents. The spatial patterning technique is straightforward and has the potential to aid on-chip analysis of single adherent cells.

We report a digital microfluidic system designed for droplet-based long-term culture and analysis of algae. The system includes unique innovations relative to standard devices including an active reservoir structure to maintain homogeneous cell density, a customized device layout capable of controlling a wide range of different droplet volumes, vertical interconnects to collect spent reagents, detection zones compatible with parallel-scale optical measurements using a standard multiwell plate reader, and optimized features for droplet dispensing in parallel. The method allows for automated, multiplexed analysis with significant reductions in human intervention, representing a decrease from 600 pipette steps (for a conventional screen in multiwell plates) to fewer than 20 (for the new microfluidic technique). The system was applied to screen conditions favourable for lipid generation in the widely used algal model for biofuel production, Cyclotella cryptica. A dependence on illumination wavelength was observed, with the best conditions (representing a four-fold increase relative to control) comprising an alternation between yellow (∼580 nm) and blue (∼450 nm) illumination wavelengths. These effects were observed for both micro- and macro-scale cultures, and are consistent with a putative mechanism involving photooxidative stress. We propose that the microfluidic system described here is an attractive new screening tool with potential advantages for applications in renewable energy, biotechnology, materials science, and beyond.

A laser-polymerized thin film for silica surface modification is presented. This technique enables photopatterned surface charge modification consistent with optical tweezer techniques. This charge modification may be applied for chip-based cell techniques and multi-dimensional separation techniques that require nonuniform zeta potential on a microfluidic chip.

We have developed a simple and fast procedure for the in-situ photopolymerization of a sol-gel monolith having a porous structure on a chip. A solution of methacryloxypropyltrimethoxysilane mixed with an acid catalyst, water, toluene, and a photoinitiator was irradiated at 365nm for 10sec∼1min in a microchip to prepare a photopolymerized sol-gel monoliths under an inverted microscope with a mercury lamp.

We propose a new methodology for the separation of the constituents of complex chemical and biological mixtures using electrophoresis combined with dielectrophoresis on a chip and laser induced fluorescence detection. We use a network of closely spaced interleaved microelectrodes to facilitate the use of dielectrophoresis as an electrical gradient “stationary phase” for bulk separations. Our new method combines the potential of dielectrophoretic separations with integrated chip electrophoreis, which offers the advantages of high throughput and of precise control of a small amount of sample volume using electroosmotically driven, high-efficiency separations of a number of chemicals and molecules.

Voltage pulses that cause changes in fluid shape or movement can be used to drive optical components and miniaturized assays.

Hydrogels are networks of hydrophilic polymer chains that are swollen with water, and they are useful for a wide range of applications because they provide stable niches for immobilizing proteins and cells. We report here the marriage of hydrogels with digital microfluidic devices. Until recently, digital microfluidics, a fluid handling technique in which discrete droplets are manipulated electromechanically on the surface of an array of electrodes, has been used only for homogeneous systems involving liquid reagents. Here, we demonstrate for the first time that the cylindrical hydrogel discs can be incorporated into digital microfluidic systems and that these discs can be systematically addressed by droplets of reagents. Droplet movement is observed to be unimpeded by interaction with the gel discs, and gel discs remain stationary when droplets pass through them. Analyte transport into gel discs is observed to be identical to diffusion in cases in which droplets are incubated with gels passively, but transport is enhanced when droplets are continually actuated through the gels. The system is useful for generating integrated enzymatic microreactors and for three-dimensional cell culture. This paper demonstrates a new combination of techniques for lab-on-a-chip systems which we propose will be useful for a wide range of applications.