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Showing papers in "Lab on a Chip in 2008"


Journal ArticleDOI
TL;DR: A novel class of fluorosurfactants that are synthesized by coupling oligomeric perfluorinated polyethers (PFPE) with polyethyleneglycol (PEG) stabilize water-in-fluorocarbon oil emulsions and can be used for in vitro translation (IVT), as well as encapsulation and incubation of single cells.
Abstract: Drops of water-in-fluorocarbon emulsions have great potential for compartmentalizing both in vitro and in vivo biological systems; however, surfactants to stabilize such emulsions are scarce. Here we present a novel class of fluorosurfactants that we synthesize by coupling oligomeric perfluorinated polyethers (PFPE) with polyethyleneglycol (PEG). We demonstrate that these block copolymer surfactants stabilize water-in-fluorocarbon oil emulsions during all necessary steps of a drop-based experiment including drop formation, incubation, and reinjection into a second microfluidic device. Furthermore, we show that aqueous drops stabilized with these surfactants can be used for in vitrotranslation (IVT), as well as encapsulation and incubation of single cells. The compatability of this emulsion system with both biological systems and polydimethylsiloxane (PDMS) microfluidic devices makes these surfactants ideal for a broad range of high-throughput, drop-based applications.

747 citations


Journal ArticleDOI
TL;DR: FLASH (Fast Lithographic Activation of Sheets), a rapid method for laboratory prototyping of microfluidic devices in paper, is described, which is based on photolithography, but requires only a UV lamp and a hotplate.
Abstract: This article describes FLASH (Fast Lithographic Activation of Sheets), a rapid method for laboratory prototyping of microfluidic devices in paper. Paper-based microfluidic devices are emerging as a new technology for applications in diagnostics for the developing world, where low cost and simplicity are essential. FLASH is based on photolithography, but requires only a UV lamp and a hotplate; no clean-room or special facilities are required (FLASH patterning can even be performed in sunlight if a UV lamp and hotplate are unavailable). The method provides channels in paper with dimensions as small as 200 µm in width and 70 µm in height; the height is defined by the thickness of the paper. Photomasks for patterning paper-based microfluidic devices can be printed using an ink-jet printer or photocopier, or drawn by hand using a waterproof black pen. FLASH provides a straightforward method for prototyping paper-based microfluidic devices in regions where the technological support for conventional photolithography is not available.

663 citations


Journal ArticleDOI
TL;DR: This review provides an overview of methods for generating, controlling and manipulating droplets and discusses 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.
Abstract: 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.

637 citations


Journal ArticleDOI
TL;DR: Microfluidic gradient generators offer greater levels of precision, quantitation, and spatiotemporal gradient control than traditional methods, and may greatly enhance the understanding of many biological phenomena.
Abstract: Biomolecule gradients have been shown to play roles in a wide range of biological processes including development, inflammation, wound healing, and cancer metastasis. Elucidation of these phenomena requires the ability to expose cells to biomolecule gradients that are quantifiable, controllable, and mimic those that are present in vivo. Here we review the major biological phenomena in which biomolecule gradients are employed, traditional in vitro gradient-generating methods developed over the past 50 years, and new microfluidic devices for generating gradients. Microfluidic gradient generators offer greater levels of precision, quantitation, and spatiotemporal gradient control than traditional methods, and may greatly enhance our understanding of many biological phenomena. For each method, we outline the salient features, capabilities, and applications.

587 citations


Journal ArticleDOI
TL;DR: A passive microfluidic device with spiral microchannel geometry for complete separation of particles that takes advantage of the dual role of Dean forces for focusing larger particles in a single equilibrium position and transposing the smaller particles from the inner half to the outer half of the microchannel cross-section.
Abstract: Microparticle separation and concentration based on size has become indispensable in many biomedical and environmental applications. In this paper we describe a passive microfluidic device with spiral microchannel geometry for complete separation of particles. The design takes advantage of the inertial lift and viscous drag forces acting on particles of various sizes to achieve differential migration, and hence separation, of microparticles. The dominant inertial forces and the Dean rotation force due to the spiral microchannel geometry cause the larger particles to occupy a single equilibrium position near the inner microchannel wall. The smaller particles migrate to the outer half of the channel under the influence of Dean forces resulting in the formation of two distinct particle streams which are collected in two separate outputs. This is the first demonstration that takes advantage of the dual role of Dean forces for focusing larger particles in a single equilibrium position and transposing the smaller particles from the inner half to the outer half of the microchannel cross-section. The 5-loop spiral microchannel 100 μm wide and 50 μm high was used to successfully demonstrate a complete separation of 7.32 μm and 1.9 μm particles at Dean number De = 0.47. Analytical analysis supporting the experiments and models is also presented. The simple planar structure of the separator offers simple fabrication and makes it ideal for integration with on-chip microfluidic systems, such as micro total analysis systems (μTAS) or lab-on-a-chip (LOC) for continuous filtration and separation applications.

582 citations


Journal ArticleDOI
TL;DR: The performance of magnetic bead-based immunoassays (cardiac troponin I) on a digital microfluidic cartridge in less than 8 minutes using whole blood samples and the capability to perform sample preparation for bacterial infectious disease pathogen, methicillin-resistant Staphylococcus aureus and for human genomic DNA using magnetic beads are demonstrated.
Abstract: Point of care testing is playing an increasingly important role in improving the clinical outcome in health care management. The salient features of a point of care device are rapid results, integrated sample preparation and processing, small sample volumes, portability, multifunctionality and low cost. In this paper, we demonstrate some of these salient features utilizing an electrowetting-based Digital Microfluidic platform. We demonstrate the performance of magnetic bead-based immunoassays (cardiac troponin I) on a digital microfluidic cartridge in less than 8 minutes using whole blood samples. Using the same microfluidic cartridge, a 40-cycle real-time polymerase chain reaction was performed within 12 minutes by shuttling a droplet between two thermal zones. We further demonstrate, on the same cartridge, the capability to perform sample preparation for bacterial infectious disease pathogen, methicillin-resistant Staphylococcus aureus and for human genomic DNA using magnetic beads. In addition to rapid results and integrated sample preparation, electrowetting-based digital microfluidic instruments are highly portable because fluid pumping is performed electronically. All the digital microfluidic chips presented here were fabricated on printed circuit boards utilizing mass production techniques that keep the cost of the chip low. Due to the modularity and scalability afforded by digital microfluidics, multifunctional testing capability, such as combinations within and between immunoassays, DNA amplification, and enzymatic assays, can be brought to the point of care at a relatively low cost because a single chip can be configured in software for different assays required along the path of care.

559 citations


Journal ArticleDOI
TL;DR: Encapsulation of cells within picolitre-size monodisperse drops provides new means to perform quantitative biological studies on a single-cell basis for large cell populations by evenly spacing cells as they travel within a high aspect-ratio microchannel.
Abstract: Encapsulation of cells within picolitre-size monodisperse drops provides new means to perform quantitative biological studies on a single-cell basis for large cell populations. Variability in the number of cells per drop due to stochastic cell loading is a major barrier to these techniques. We overcome this limitation by evenly spacing cells as they travel within a high aspect-ratio microchannel; cells enter the drop generator with the frequency of drop formation.

549 citations


Journal ArticleDOI
TL;DR: It is shown that single hybridoma cells in 33 pL drops secrete detectable concentrations of antibodies in only 6 h and remain fully viable and highly flexible and adaptable to a variety of cell-based assays.
Abstract: We use microfluidic devices to encapsulate, incubate, and manipulate individual cells in picoliter aqueous drops in a carrier fluid at rates of up to several hundred Hz. We use a modular approach with individual devices for each function, thereby significantly increasing the robustness of our system and making it highly flexible and adaptable to a variety of cell-based assays. The small volumes of the drops enables the concentrations of secreted molecules to rapidly attain detectable levels. We show that single hybridoma cells in 33 pL drops secrete detectable concentrations of antibodies in only 6 h and remain fully viable. These devices hold the promise of developing microfluidic cell cytometers and cell sorters with much greater functionality, allowing assays to be performed on individual cells in their own microenvironment prior to analysis and sorting.

535 citations


Journal ArticleDOI
TL;DR: This review examines the innovative techniques which have recently been developed to address the difficulty in producing low-cost, sensitive, and portable optical detection systems for point-of-care (POC) diagnostics.
Abstract: Despite a growing focus from the academic community, the field of microfluidics has yet to produce many commercial devices for point-of-care (POC) diagnostics. One of the main reasons for this is the difficulty in producing low-cost, sensitive, and portable optical detection systems. Although electrochemical methods work well for certain applications, optical detection is generally regarded as superior and is the method most widely employed in laboratory clinical chemistry. Conventional optical systems, however, are costly, require careful alignment, and do not translate well to POC devices. Furthermore, many optical detection paradigms such as absorbance and fluorescence suffer at smaller geometries because the optical path length through the sample is shortened. This review examines the innovative techniques which have recently been developed to address these issues. We highlight microfluidic diagnostic systems which demonstrate practical integration of sample preparation, analyte enrichment, and optical detection. We also examine several emerging detection paradigms involving nanoengineered materials which do not suffer from the same miniaturization disadvantages as conventional measurements.

486 citations


Journal ArticleDOI
TL;DR: A novel on-chip microparticle focusing technique using standing surface acoustic waves (SSAW) is introduced, which is simple, fast, dilution-free, and applicable to virtually any type of microparticles.
Abstract: We introduce a novel on-chip microparticle focusing technique using standing surface acoustic waves (SSAW). Our method is simple, fast, dilution-free, and applicable to virtually any type of microparticle.

425 citations


Journal ArticleDOI
TL;DR: In this article, a plug-based microfluidic technology that enables rapid detection and drug susceptibility screening of bacteria in samples, including complex biological matrices, without pre-incubation is described.
Abstract: This article describes plug-based microfluidic technology that enables rapid detection and drug susceptibility screening of bacteria in samples, including complex biological matrices, without pre-incubation. Unlike conventional bacterial culture and detection methods, which rely on incubation of a sample to increase the concentration of bacteria to detectable levels, this method confines individual bacteria into droplets nanoliters in volume. When single cells are confined into plugs of small volume such that the loading is less than one bacterium per plug, the detection time is proportional to plug volume. Confinement increases cell density and allows released molecules to accumulate around the cell, eliminating the pre-incubation step and reducing the time required to detect the bacteria. We refer to this approach as ‘stochastic confinement’. Using the microfluidic hybrid method, this technology was used to determine the antibiogram – or chart of antibiotic sensitivity – of methicillin-resistant Staphylococcus aureus (MRSA) to many antibiotics in a single experiment and to measure the minimal inhibitory concentration (MIC) of the drug cefoxitin (CFX) against this strain. In addition, this technology was used to distinguish between sensitive and resistant strains of S. aureus in samples of human blood plasma. High-throughput microfluidic techniques combined with single-cell measurements also enable multiple tests to be performed simultaneously on a single sample containing bacteria. This technology may provide a method of rapid and effective patient-specific treatment of bacterial infections and could be extended to a variety of applications that require multiple functional tests of bacterial samples on reduced timescales.

Journal ArticleDOI
TL;DR: The mass production of monodisperse emulsion droplets and particles using microfluidic large-scale integration on a chip is reported, using a module having 128 cross-junctions arranged circularly on a 4 cm x 4 cm chip.
Abstract: In this study, we report the mass production of monodisperse emulsion droplets and particles using microfluidic large-scale integration on a chip. The production module comprises a glass microfluidic chip with planar microfabricated 16–256 droplet-formation units (DFUs) and a palm-sized stainless steel holder having several layers for supplying liquids into the inlets of the mounted chip. By using a module having 128 cross-junctions (i.e., 256 DFUs) arranged circularly on a 4 cm × 4 cm chip, we could produce droplets of photopolymerizable acrylate monomer at a throughput of 320.0 mL h−1. The product was monodisperse, having a mean diameter of 96.4 µm, with a coefficient of variation (CV) of 1.3%. Subsequent UV polymerization off the module yielded monodisperse acrylic microspheres at a throughput of ∼0.3 kg h−1. Another module having 128 co-flow geometries could produce biphasic Janus droplets of black and white segments at 128.0 mL h−1. The product had a mean diameter of 142.3 µm, with a CV of 3.3%. This co-flow module could also be applied in the mass production of homogeneous monomer droplets.

Journal ArticleDOI
TL;DR: It is shown that the merging of droplet interfaces occurs within both compressing and the decompressing regimes, and 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.
Abstract: 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.

Journal ArticleDOI
TL;DR: A digital microfluidic platform for performing heterogeneous sandwich immunoassays based on efficient handling of magnetic beads is presented in this paper, based on manipulation of discrete droplets of samples and reagents using electrowetting without the need for channels where the droplets are free to move laterally.
Abstract: A digital microfluidic platform for performing heterogeneous sandwich immunoassays based on efficient handling of magnetic beads is presented in this paper. This approach is based on manipulation of discrete droplets of samples and reagents using electrowetting without the need for channels where the droplets are free to move laterally. Droplet-based manipulation of magnetic beads therefore does not suffer from clogging of channels. Immunoassays on a digital microfluidic platform require the following basic operations: bead attraction, bead washing, bead retention, and bead resuspension. Several parameters such as magnetic field strength, pull force, position, and buffer composition were studied for effective bead operations. Dilution-based washing of magnetic beads was demonstrated by immobilizing the magnetic beads using a permanent magnet and splitting the excess supernatant using electrowetting. Almost 100% bead retention was achieved after 7776-fold dilution-based washing of the supernatant. Efficient resuspension of magnetic beads was achieved by transporting a droplet with magnetic beads across five electrodes on the platform and exploiting the flow patterns within the droplet to resuspend the beads. All the magnetic-bead droplet operations were integrated together to generate standard curves for sandwich heterogeneous immunoassays on human insulin and interleukin-6 (IL-6) with a total time to result of 7 min for each assay.

Journal ArticleDOI
TL;DR: Digital microfluidics (DMF) has great potential as a simple yet versatile analytical tool for implementing cell-based assays on the microscale because of automated manipulation of multiple reagents in addition to reduced reagent use and analysis time.
Abstract: We introduce a new method for implementing cell-based assays. The method is based on digital microfluidics (DMF) which is used to actuate nanolitre droplets of reagents and cells on a planar array of electrodes. We demonstrate that this method is advantageous for cell-based assays because of automated manipulation of multiple reagents in addition to reduced reagent use and analysis time. No adverse effects of actuation by DMF were observed in assays for cell viability, proliferation, and biochemistry. A cytotoxicity assay using Jurkat T-cells was performed using the new method, which had ∼ 20 times higher sensitivity than a conventional well plate assay. These results suggest that DMF has great potential as a simple yet versatile analytical tool for implementing cell-based assays on the microscale.

Journal ArticleDOI
TL;DR: This study introduces a microfluidic platform for 3D cell culture in biologically derived or synthetic hydrogels with the capability to monitor cellular dynamics in response to changes in their microenvironment and demonstrates the ability to generate gradients, surface shear, interstitial flow, and image cells in situ.
Abstract: New and more biologically relevant in vitro models are needed for use in drug development, regenerative medicine, and fundamental scientific investigation. While the importance of the extracellular microenvironment is clear, the ability to investigate the effects of physiologically relevant biophysical and biochemical factors is restricted in traditional cell culture platforms. Moreover, the versatility for multi-parameter manipulation, on a single platform, with the optical resolution to monitor the dynamics of individual cells or small population is lacking. Here we introduce a microfluidic platform for 3D cell culture in biologically derived or synthetic hydrogels with the capability to monitor cellular dynamics in response to changes in their microenvironment. Direct scaffold microinjection, was employed to incorporate 3D matrices into microfluidic devices. Our system geometry permits a unique window for studying directional migration, e.g.sprouting angiogenesis, since sprouts grow predominantly in the microscopic viewing plane. In this study, we demonstrate the ability to generate gradients (non-reactive solute), surface shear, interstitial flow, and image cellsin situ. Three different capillary morphogenesis assays are demonstrated. Human adult dermal microvascular endothelial cells (HMVEC-ad) were maintained in culture for up to 7 days during which they formed open lumen-like structures which was confirmed with confocal microscopy and by perfusion with fluorescent microspheres. In the sprouting assay, time-lapse movies revealed cellular mechanisms and dynamics (filopodial projection/retraction, directional migration, cell division and lumen formation) during tip-cell invasion of underlying 3D matrix and subsequent lumen formation.

Journal ArticleDOI
Adam R. Abate1, Daeyeon Lee1, Thao Do1, Christian Holtze1, David A. Weitz1 
TL;DR: This paper presents a method to coat PDMS channels with a glass-like layer using sol-gel chemistry, which greatly increases chemical resistance of the channels and can be functionalized with a wide range of chemicals to precisely control interfacial properties.
Abstract: Soft lithography using polydimethylsiloxane (PDMS) allows one to fabricate complex microfluidic devices easily and at low cost. However, PDMS swells in the presence of many organic solvents significantly degrading the performance of the device. We present a method to coat PDMS channels with a glass-like layer using sol–gel chemistry. This coating greatly increases chemical resistance of the channels; moreover, it can be functionalized with a wide range of chemicals to precisely control interfacial properties. This method combines the ease of fabrication afforded by soft-lithography with the precision control and chemical robustness afforded by glass.

Journal ArticleDOI
TL;DR: This paper describes, for the first time, the fabrication of large numbers of cell-laden microgel particles using a continuous microfluidic process called stop-flow lithography (SFL), which may become a useful tool for generating cell-filled microgels for various biomedical applications.
Abstract: Encapsulating cells within hydrogels is important for generating three-dimensional (3D) tissue constructs for drug delivery and tissue engineering. This paper describes, for the first time, the fabrication of large numbers of cell-laden microgel particles using a continuous microfluidic process called stop-flow lithography (SFL). Prepolymer solution containing cells was flowed through a microfluidic device and arrays of individual particles were repeatedly defined using pulses of UV light through a transparency mask. Unlike photolithography, SFL can be used to synthesize microgel particles continuously while maintaining control over particle size, shape and anisotropy. Therefore, SFL may become a useful tool for generating cell-laden microgels for various biomedical applications.

Journal ArticleDOI
TL;DR: With the ability to make truly molecular-scale filters and pores with well-defined sizes, shapes, and surface properties, now the authors are well positioned to engineer better functionality in molecular sieving, separation and other membrane applications.
Abstract: Filtration of molecules by nanometer-sized structures is ubiquitous in our everyday life, but our understanding of such molecular filtration processes is far less than desired. Until recently, one of the main reasons was the lack of experimental methods that can help provide detailed, microscopic pictures of molecule–nanostructure interactions. Several innovations in experimental methods, such as nuclear track-etched membranes developed in the 70s, and more recent development of nanofluidic molecular filters, played pivotal roles in advancing our understanding. With the ability to make truly molecular-scale filters and pores with well-defined sizes, shapes, and surface properties, now we are well positioned to engineer better functionality in molecular sieving, separation and other membrane applications. Reviewing past theoretical developments (often scattered across different fields) and connecting them to the most recent advances in the field would be essential to get a full, unified view on this important engineering question.

Journal ArticleDOI
TL;DR: A high-throughput microfluidics-based 'biophysical' flow cytometry technique that measures single-cell transit times of blood cell populations passing through in vitro capillary networks to characterize biophysical changes in two model disease states in which mechanical properties of cells are thought to lead to microvascular obstruction.
Abstract: Pathological processes in hematologic diseases originate at the single-cell level, often making measurements on individual cells more clinically relevant than population averages from bulk analysis. For this reason, flow cytometry has been an effective tool for single-cell analysis of properties using light scattering and fluorescence labeling. However, conventional flow cytometry cannot measure cell mechanical properties, alterations of which contribute to the pathophysiology of hematologic diseases such as sepsis, diabetic retinopathy, and sickle cell anemia. Here we present a high-throughput microfluidics-based ‘biophysical’ flow cytometry technique that measures single-cell transit times of blood cell populations passing through in vitro capillary networks. To demonstrate clinical relevance, we use this technique to characterize biophysical changes in two model disease states in which mechanical properties of cells are thought to lead to microvascular obstruction: (i) sepsis, a process in which inflammatory mediators in the bloodstream activate neutrophils and (ii) leukostasis, an often fatal and poorly understood complication of acute leukemia. Using patient samples, we show that cell transit time through and occlusion of microfluidic channels is increased for both disease states compared to control samples, and we find that mechanical heterogeneity of blood cell populations is a better predictor of microvascular obstruction than average properties. Inflammatory mediators involved in sepsis were observed to significantly affect the shape and magnitude of the neutrophil transit time population distribution. Altered properties of leukemia cell subpopulations, rather than of the population as a whole, were found to correlate with symptoms of leukostasis in patients—a new result that may be useful for guiding leukemia therapy. By treating cells with drugs that affect the cytoskeleton, we also demonstrate that their transit times could be significantly reduced. Biophysical flow cytometry offers a low-cost and high-throughput diagnostic and drug discovery platform for hematologic diseases that affect microcirculatory flow.

Journal ArticleDOI
TL;DR: Progress toward development of disposable, low-cost, easy-to-use microfluidics-based diagnostics that require no instrument at all is reviewed.
Abstract: In many health care settings, it is uneconomical, impractical, or unaffordable to maintain and access a fully equipped diagnostics laboratory. Examples include home health care, developing-country health care, and emergency situations in which first responders are dealing with pandemics or biowarfare agent release. In those settings, fully disposable diagnostic devices that require no instrument support, reagent, or significant training are well suited. Although the only such technology to have found widespread adoption so far is the immunochromatographic rapid assay strip test, microfluidics holds promise to expand the range of assay technologies that can be performed in formats similar to that of a strip test. In this paper, we review progress toward development of disposable, low-cost, easy-to-use microfluidics-based diagnostics that require no instrument at all. We also present examples of microfluidic functional elements—including mixers, separators, and detectors—as well as complete microfluidic devices that function entirely without any moving parts and external power sources.

Journal ArticleDOI
TL;DR: This work fabricated artificial cilia consisting of electro-statically actuated polymer structures, and have integrated these in a micro-fluidic channel, and shows that the cilia can generate substantial fluid velocities, up to 0.6 mm s(-1).
Abstract: In lab-on-chip devices, on which complete (bio-)chemical analysis laboratories are miniaturized and integrated, it is essential to manipulate fluids in sub-millimetre channels and sub-microlitre chambers. A special challenge in these small micro-fluidic systems is to create good mixing flows, since it is almost impossible to generate turbulence. We propose an active micro-fluidic mixing concept inspired by nature, namely by micro-organisms that swim through a liquid by oscillating microscopic hairs, cilia, that cover their surface. We have fabricated artificial cilia consisting of electro-statically actuated polymer structures, and have integrated these in a micro-fluidic channel. Flow visualization experiments show that the cilia can generate substantial fluid velocities, up to 0.6 mm s−1. In addition, very efficient mixing is obtained using specially designed geometrical cilia configurations in a micro-channel. Since the artificial cilia can be actively controlled using electrical signals, they have exciting applications in micro-fluidic devices.

Journal ArticleDOI
TL;DR: A droplet-based microfluidic system integrating a droplets generator and a droplet trap array is described for encapsulating individual Caenorhabditis elegans into a parallel series of droplets, enabling characterization of the worm behavior in response to neurotoxin at single-animal resolution.
Abstract: A droplet-based microfluidic system integrating a droplet generator and a droplet trap array is described for encapsulating individual Caenorhabditis elegans into a parallel series of droplets, enabling characterization of the worm behavior in response to neurotoxin at single-animal resolution.

Journal ArticleDOI
TL;DR: An integrated microfluidic device with on-chip pumping and detection functionalities that may have applications in toxicity testing and drug screening is developed.
Abstract: Conventional cell-based assays in life science and medical applications can be difficult to maintain functionally over long periods. Microfluidics is an emerging technology with potential to provide integrated environments for cell maintenance, continuous perfusion, and monitoring. In this study, we developed an integrated microfluidic device with on-chip pumping and detection functionalities. The microfluidic structure in the device is divided into two independent channels separated by a semipermeable membrane on which cells are inoculated and cultured. Perfusion and fluorescence measurements of culture media for each channel can be conducted by the on-chip pumping system and optical fiber detection system. Performance of the device was examined through long-term culture and monitoring of polarized transport activity of intestinal tissue models (Caco-2 cells). The cells could be cultured for more than two weeks, and monolayer transport of rhodamine 123 was successfully monitored by on-line fluorescent measurement. This device may have applications in toxicity testing and drug screening.


Journal ArticleDOI
TL;DR: An all-electronic (i.e., no ancillary pumping) real-time feedback control of on-chip droplet generation with significant improvement in the droplet volume uniformity, compared with an open loop control as well as the previous feedback control employing an external pump.
Abstract: Electrowetting-on-dielectric (EWOD) actuation enables digital (or droplet) microfluidics where small packets of liquids are manipulated on a two-dimensional surface. Due to its mechanical simplicity and low energy consumption, EWOD holds particular promise for portable systems. To improve volume precision of the droplets, which is desired for quantitative applications such as biochemical assays, existing practices would require near-perfect device fabrication and operation conditions unless the droplets are generated under feedback control by an extra pump setup off of the chip. In this paper, we develop an all-electronic (i.e., no ancillary pumping) real-time feedback control of on-chip droplet generation. A fast voltage modulation, capacitance sensing, and discrete-time PID feedback controller are integrated on the operating electronic board. A significant improvement is obtained in the droplet volume uniformity, compared with an open loop control as well as the previous feedback control employing an external pump. Furthermore, this new capability empowers users to prescribe the droplet volume even below the previously considered minimum, allowing, for example, 1 : x (x < 1) mixing, in comparison to the previously considered n : m mixing (i.e., n and m unit droplets).

Journal ArticleDOI
TL;DR: A microfluidic approach is reported that can extract total mRNA from individual single-cells and synthesize cDNA on the same device with high mRNA-to-cDNA efficiency, which makes large-scale single-cell gene expression profiling possible.
Abstract: The gene expression of human embryonic stem cells (hESC) is a critical aspect for understanding the normal and pathological development of human cells and tissues. Current bulk gene expression assays rely on RNA extracted from cell and tissue samples with various degree of cellular heterogeneity. These ‘cell population averaging’ data are difficult to interpret, especially for the purpose of understanding the regulatory relationship of genes in the earliest phases of development and differentiation of individual cells. Here, we report a microfluidic approach that can extract total mRNA from individual single-cells and synthesize cDNA on the same device with high mRNA-to-cDNA efficiency. This feature makes large-scale single-cell gene expression profiling possible. Using this microfluidic device, we measured the absolute numbers of mRNA molecules of three genes (B2M, Nodal and Fzd4) in a single hESC. Our results indicate that gene expression data measured from cDNA of a cell population is not a good representation of the expression levels in individual single cells. Within the G0/G1 phase pluripotent hESC population, some individual cells did not express all of the 3 interrogated genes in detectable levels. Consequently, the relative expression levels, which are broadly used in gene expression studies, are very different between measurements from population cDNA and single-cell cDNA. The results underscore the importance of discrete single-cell analysis, and the advantages of a microfluidic approach in stem cell gene expression studies.

Journal ArticleDOI
TL;DR: The proof-of-principle is demonstrated of a new lens-free cell monitoring platform that involves using an opto-electronic sensor array to record the shadow image of cells onto the sensor plane that does not require any mechanical scanning or optical elements, such as microscope objectives or lenses.
Abstract: We experimentally and theoretically demonstrate the proof-of-principle of a new lens-free cell monitoring platform that involves using an opto-electronic sensor array to record the shadow image of cells onto the sensor plane This technology can monitor/count cells over a field-of-view that is more than two orders of magnitude larger than that of a conventional light microscope Furthermore, it does not require any mechanical scanning or optical elements, such as microscope objectives or lenses We also show that this optical approach can conveniently be combined with microfluidic channels, enabling parallel on-chip monitoring of various different cell types, eg, blood cells, NIH-3T3 fibroblasts, murine embryonic stem cells, AML-12 hepatocytes An important application of this approach could be a miniaturized point-of-care technology to obtain CD4 T lymphocyte counts of HIV infected patients in resource limited settings

Journal ArticleDOI
TL;DR: A microfluidic device was designed and fabricated to generate stable concentration gradients of biomolecules in a cell culture chamber while minimizing the fluid shear stress experienced by the cells, suggesting a two-part requirement to induce VEGF chemotaxis.
Abstract: The directed migration of endothelial cells is an early and critical step in angiogenesis, or new blood vessel formation. In this study, the polarization and chemotaxis of human umbilical vein endothelial cells (HUVEC) in response to quantified gradients of vascular endothelial growth factor (VEGF) were examined. To accomplish this, a microfluidic device was designed and fabricated to generate stable concentration gradients of biomolecules in a cell culture chamber while minimizing the fluid shear stress experienced by the cells. Finite element simulation of the device geometry produced excellent agreement with the observed VEGF concentration distribution, which was found to be stable across multiple hours. This device is expected to have wide applicability in the study of shear-sensitive cells such as HUVEC and non-adherent cell types as well as in the study of migration through three-dimensional matrices. HUVEC were observed to chemotax towards higher VEGF concentrations across the entire range of concentrations studied (18–32 ng mL−1) when the concentration gradient was 14 ng mL−1 mm−1. In contrast, shallow gradients (2 ng mL−1 mm−1) across the same concentration range were unable to induce HUVEC chemotaxis. Furthermore, while all HUVEC exposed to elevated VEGF levels (both in steep and shallow gradients) displayed an increased number of filopodia, only chemotaxing HUVEC displayed an asymmetric distribution of filopodia, with enhanced numbers of protrusions present along the leading edge. These results suggest a two-part requirement to induce VEGF chemotaxis: the VEGF absolute concentration enhances the total number of filopodia extended while the VEGF gradient steepness induces filopodia localization, cell polarization, and subsequent directed migration.

Journal ArticleDOI
TL;DR: This printing method even allows fabricating a parallel array of preconcentrators to increase the concentrated sample volume, which can facilitate an integration of the microfluidic preconcentrator chip as a signal enhancing tool to various detectors such as a mass spectrometer.
Abstract: In this paper, we report a new method of fabricating a high-throughput protein preconcentrator in poly(dimethylsiloxane) (PDMS) microfluidic chip format. We print a submicron thick ion-selective membrane on the glass substrate by using standard patterning techniques. By simply plasma-bonding a PDMS microfluidic device on top of the printed glass substrate, we can integrate the ion-selective membrane into the device and rapidly prototype a PDMS preconcentrator without complicated microfabrication and cumbersome integration processes. The PDMS preconcentrator shows a concentration factor as high as ∼104 in 5 min. This printing method even allows fabricating a parallel array of preconcentrators to increase the concentrated sample volume, which can facilitate an integration of our microfluidic preconcentrator chip as a signal enhancing tool to various detectors such as a mass spectrometer.