Showing papers on "Microfluidics published in 2005"
TL;DR: A review of the physics of small volumes (nanoliters) of fluids is presented, as parametrized by a series of dimensionless numbers expressing the relative importance of various physical phenomena as mentioned in this paper.
Abstract: Microfabricated integrated circuits revolutionized computation by vastly reducing the space, labor, and time required for calculations. Microfluidic systems hold similar promise for the large-scale automation of chemistry and biology, suggesting the possibility of numerous experiments performed rapidly and in parallel, while consuming little reagent. While it is too early to tell whether such a vision will be realized, significant progress has been achieved, and various applications of significant scientific and practical interest have been developed. Here a review of the physics of small volumes (nanoliters) of fluids is presented, as parametrized by a series of dimensionless numbers expressing the relative importance of various physical phenomena. Specifically, this review explores the Reynolds number Re, addressing inertial effects; the Peclet number Pe, which concerns convective and diffusive transport; the capillary number Ca expressing the importance of interfacial tension; the Deborah, Weissenberg, and elasticity numbers De, Wi, and El, describing elastic effects due to deformable microstructural elements like polymers; the Grashof and Rayleigh numbers Gr and Ra, describing density-driven flows; and the Knudsen number, describing the importance of noncontinuum molecular effects. Furthermore, the long-range nature of viscous flows and the small device dimensions inherent in microfluidics mean that the influence of boundaries is typically significant. A variety of strategies have been developed to manipulate fluids by exploiting boundary effects; among these are electrokinetic effects, acoustic streaming, and fluid-structure interactions. The goal is to describe the physics behind the rich variety of fluid phenomena occurring on the nanoliter scale using simple scaling arguments, with the hopes of developing an intuitive sense for this occasionally counterintuitive world.
4,044 citations
TL;DR: In this paper, the authors compare the various approaches used to derive the basic electrowetting equation, which has been shown to be very reliable as long as the applied voltage is not too high.
Abstract: Electrowetting has become one of the most widely used tools for manipulating tiny amounts of liquids on surfaces. Applications range from 'lab-on-a-chip' devices to adjustable lenses and new kinds of electronic displays. In the present article, we review the recent progress in this rapidly growing field including both fundamental and applied aspects. We compare the various approaches used to derive the basic electrowetting equation, which has been shown to be very reliable as long as the applied voltage is not too high. We discuss in detail the origin of the electrostatic forces that induce both contact angle reduction and the motion of entire droplets. We examine the limitations of the electrowetting equation and present a variety of recent extensions to the theory that account for distortions of the liquid surface due to local electric fields, for the finite penetration depth of electric fields into the liquid, as well as for finite conductivity effects in the presence of AC voltage. The most prominent failure of the electrowetting equation, namely the saturation of the contact angle at high voltage, is discussed in a separate section. Recent work in this direction indicates that a variety of distinct physical effects?rather than a unique one?are responsible for the saturation phenomenon, depending on experimental details. In the presence of suitable electrode patterns or topographic structures on the substrate surface, variations of the contact angle can give rise not only to continuous changes of the droplet shape, but also to discontinuous morphological transitions between distinct liquid morphologies. The dynamics of electrowetting are discussed briefly. Finally, we give an overview of recent work aimed at commercial applications, in particular in the fields of adjustable lenses, display technology, fibre optics, and biotechnology-related microfluidic devices.
1,962 citations
TL;DR: A versatile new strategy for producing monodisperse solid particles with sizes from 20 to 1000 mm by using a microfluidic device and shaping the droplets in a microchannel and then solidifying these drops in situ either by polymerizing a liquid monomer or by lowering the temperature of a liquid that sets thermally.
Abstract: Herein we describe a versatile new strategy for producing monodisperse solid particles with sizes from 20 to 1000 mm. The method involves the formation of monodisperse liquid droplets by using a microfluidic device and shaping the droplets in a microchannel and then solidifying these drops in situ either by polymerizing a liquid monomer or by lowering the temperature of a liquid that sets thermally. This method has the following features: 1) It produces particles with an exceptionally narrow range of sizes. 2) A new level of control over the shapes of the particles is offered. 3) The mechanism for droplet formation allows the use of a wide variety of materials including gels, metals, polymers, and polymers doped with functional additives. 4) The procedure can be scaled up to produce large numbers of particles. A number of methods exist for making inorganic and organic particles with narrow polydispersity. Inorganic colloids are typically prepared by precipitation reactions from organometallic precursors. Polymer colloids with sizes from 20 nm to approximately 1 mm are usually prepared by a variation of emulsion polymerization techniques. Larger beads are accessible through miniemulsion polymerization,
882 citations
TL;DR: The controlled synthesis of nonspherical microparticles using microfluidics processing is described, where plugs and disks of different lengths and diameters were obtained by varying the flow rates of the two phases.
Abstract: The controlled synthesis of nonspherical microparticles using microfluidics processing is described. Polymer droplets, formed by shearing a photopolymer using a continuous water phase at a T-junction, were constrained to adopt nonspherical shapes by confining them using appropriate microchannel geometries. Plugs were obtained by shearing the polymer phase at low shear rates, while disks were obtained by flattening droplets using a channel of low height. The nonspherical shapes formed were permanently preserved by photopolymerizing the constrained droplets in situ using ultraviolet light. Monodisperse plugs and disks of different lengths and diameters were obtained by varying the flow rates of the two phases.
462 citations
TL;DR: This review describes recent developments in microfabricated flow cytometers and related microfluidic devices that can detect, analyze, and sort cells or particles and presents various efforts that take advantage of novel microscale flow phenomena and microFabrication techniques to build microfluidity cell analysis systems.
Abstract: This review describes recent developments in microfabricated flow cytometers and related microfluidic devices that can detect, analyze, and sort cells or particles. The high-speed analytical capabilities of flow cytometry depend on the cooperative use of microfluidics, optics and electronics. Along with the improvement of other components, replacement of conventional glass capillary-based fluidics with microfluidic sample handling systems operating in microfabricated structures enables volume- and power-efficient, inexpensive and flexible analysis of particulate samples. In this review, we present various efforts that take advantage of novel microscale flow phenomena and microfabrication techniques to build microfluidic cell analysis systems.
449 citations
01 Jan 2005
TL;DR: In this paper, the authors achieved the synthesis of an [18F]fluoride-radiolabeled molecular imaging probe, 2-deoxy-2-[18F]-fluoro-dglucose ([18 F]FDG), in an integrated microfluidic device.
Abstract: Microreactor technology has shown potential for optimizing synthetic efficiency, particularly in preparing sensitive compounds. We achieved the synthesis of an [18F]fluoride-radiolabeled molecular imaging probe, 2-deoxy-2-[18F]fluoro-d-glucose ([18F]FDG), in an integrated microfluidic device. Five sequential processes—[18F]fluoride concentration, water evaporation, radiofluorination, solvent exchange, and hydrolytic deprotection—proceeded with high radio-chemical yield and purity and with shorter synthesis time relative to conventional automated synthesis. Multiple doses of [18F]FDG for positron emission tomography imaging studies in mice were prepared. These results, which constitute a proof of principle for automated multistep syntheses at the nanogram to microgram scale, could be generalized to a range of radiolabeled substrates.
416 citations
TL;DR: In this article, Joanicot and Ajdari discuss recent developments in droplet creation and management within microfluidic devices, and present new methods for microscale control, combined with better theoretical understanding, will result in precise handling of chemical processes at the single-droplet level and engineering of new materials.
Abstract: Future applications of microfluidic technology--in which nanoliter quantities of chemicals are processed and reacted, perhaps on an integrated chip--would immensely benefit from exquisite control of small droplets. In their Perspective,
Joanicot and Ajdari
discuss recent developments in droplet creation and management within microfluidic devices. New methods for microscale control, combined with better theoretical understanding, will result in precise handling of chemical processes at the single-droplet level and engineering of new materials.
358 citations
TL;DR: A biological analysis chip with integrated DNA amplification by PCR and hybridization was designed and was able to detect a single nucleotide polymorphism (SNP) responsible for the Leiden Factor V syndrome from human blood.
Abstract: We have developed a microfluidic device operating at a planar surface instead of a closed channel network. The fluid is transported in single droplets using surface acoustic waves (SAW) on a piezoelectric LiNbO3 substrate. The surface of the piezo is chemically structured to induce high contact angles of the droplets or enclose areas where the liquid can wet the substrate. Combining the SAW technique with thin film resistance heaters, a biological analysis chip with integrated DNA amplification by PCR and hybridization was designed. To prevent evaporation of the PCR reagents at high temperatures the sample is enclosed in droplets of mineral oil. On this chip the SAW resolves dried primers, shifts the oil capped liquid between the two heaters and mixes during hybridization. The chip is able to perform a highly sensitive, fast and specific PCR with a volume as low as 200 nl. During the temperature cycles an online monitoring of the DNA concentration is feasible with an optical unit, providing a sensitivity of 0.1 ng. After PCR the product is moved to the second heater for the hybridization on a spotted DNA array. With our chip we were able to detect a single nucleotide polymorphism (SNP) responsible for the Leiden Factor V syndrome from human blood.
350 citations
TL;DR: Arrays of nanoliter-sized plugs of different compositions can be preformed in a three-phase liquid/liquid/gas flow and transported into a microfluidic channel to test against a target, as demonstrated in protein crystallization and an enzymatic assay.
Abstract: Plugging a gap in screening: Arrays of nanoliter-sized plugs of different compositions can be preformed in a three-phase liquid/liquid/gas flow. The arrays can be transported into a microfluidic channel to test against a target (see schematic representation), as demonstrated in protein crystallization and an enzymatic assay.
259 citations
TL;DR: This review is an account of the efforts to develop a versatile and flexible microfluidic technology for surface‐processing applications and miniaturizing biological assays and addresses some of the major challenges for confining chemical and biochemical processes on surfaces.
Abstract: This review is an account of our efforts to develop a versatile and flexible microfluidic technology for surface-processing applications and miniaturizing biological assays. The review is presented in the context of current trends in microfluidic technology and addresses some of the major challenges for confining chemical and biochemical processes on surfaces: the sealing of a microchannel with a surface, the world-to-chip interface, the displacement of liquids in small conduits, the sequential delivery of multiple solutions, the accurate patterning of surfaces, the coincident detection of various analytes, and the detection of analytes in a small and dilute sample. Our solutions to these problems include the use of reversible sealing, capillary phenomena for powering and controlling liquid transport, and non-contact microfluidics for spotting and drawing (on surfaces) with flow conditions. These solutions offer many advantages over conventional techniques for handling minute amounts of liquids and may find applications in lithography, biopatterning (e.g., the patterning of biomolecules), diagnostics, drug discovery, and also cellular assays.
252 citations
TL;DR: Many constraints imposed by the monolithic construction of microfluidic channels can now be circumvented using an MFP, opening up new avenues for micro fluidic processing.
Abstract: Microfluidic systems allow (bio)chemical processes to be miniaturized with the benefit of shorter time-to-result, parallelism, reduced sample consumption, laminar flow, and increased control and efficiency. However, such miniaturization inherently limits the size of the solid objects that can be processed and entails new challenges such as the interfacing of macroscopic samples with microscopic conduits. Here, we report a microfluidic probe (MFP) that overcomes these problems by combining the concepts of 'microfluidics' and of 'scanning probes'. Here, liquid boundaries formed by hydrodynamic forces underneath the MFP confine a flow of processing solution and replace the solid walls of closed microchannels. The MFP is therefore mobile and can be used to process large surfaces and objects by scanning across them. We illustrate the versatility of this concept with several examples including protein microarraying, complex gradient-formation, multiphase laminar-flow patterning, erasing, localized staining of cells and the contact-free detachment of a single cell. Many constraints imposed by the monolithic construction of microfluidic channels can now be circumvented using an MFP, opening up new avenues for microfluidic processing.
TL;DR: Nanoliter-sized plugs--aqueous droplets surrounded by a fluorinated carrier fluid--have been applied to the screening of protein crystallization conditions, andformed arrays of plugs in capillary cartridges enable sparse matrix screening.
TL;DR: The theoretical modeling of these immunoassay applications is presented where a finite difference algorithm is applied to delineate the role of the transport of analyte molecules in the microchannel, the kinetics of binding between the analyte and the capture antibodies, and the surface density of the capture antibody on the assay.
Abstract: Microfluidics are emerging as a promising technology for miniaturizing biological assays for applications in diagnostics and research in life sciences because they enable the parallel analysis of multiple analytes with economy of samples and in short time. We have previously developed microfluidic networks for surface immunoassays where antibodies that are immobilized on one wall of a microchannel capture analytes flowing in the microchannel. This technology is capable of detecting analytes with picomolar sensitivity and from sub-microliter volume of sample within 45 min. This paper presents the theoretical modeling of these immunoassays where a finite difference algorithm is applied to delineate the role of the transport of analyte molecules in the microchannel (convection and diffusion), the kinetics of binding between the analyte and the capture antibodies, and the surface density of the capture antibody on the assay. The model shows that assays can be greatly optimized by varying the flow velocity of the solution of analyte in the microchannels. The model also shows how much the analyte-antibody binding constant and the surface density of the capture antibodies influence the performance of the assay. We then derive strategies to optimize assays toward maximal sensitivity, minimal sample volume requirement or fast performance, which we think will allow further development of microfluidic networks for immunoassay applications.
TL;DR: In this article, the authors present experiments and simulations of magnetic separation of magnetic beads in a microfluidic channel using micro-fabricated electromagnets, and the results of their simulations using FEMLAB and Mathematica are compared with experimental results obtained using their own micro-manufactured systems.
TL;DR: In this paper, a fully automated microfluidic system for the DNA amplification process by integrating an electroosmotic pump, an active micromixer and an on-chip temperature control system is presented.
Abstract: The present paper reports a fully automated microfluidic system for the DNA amplification process by integrating an electroosmotic pump, an active micromixer and an on-chip temperature control system. In this DNA amplification process, the cell lysis is initially performed in a micro cell lysis reactor. Extracted DNA samples, primers and reagents are then driven electroosmotically into a mixing region where they are mixed by the active micromixer. The homogeneous mixture is then thermally cycled in a micro-PCR (polymerase chain reaction) chamber to perform DNA amplification. Experimental results show that the proposed device can successfully automate the sample pretreatment operation for DNA amplification, thereby delivering significant time and effort savings. The new microfluidic system, which facilitates cell lysis, sample driving/mixing and DNA amplification, could provide a significant contribution to ongoing efforts to miniaturize bio-analysis systems by utilizing a simple fabrication process and cheap materials.
TL;DR: In this article, the authors demonstrate the fabrication and rotation of microgears based on the principle of form birefringence, which may be readily rotated by manipulating the input polarization in a standard optical trap.
Abstract: The reflection and refraction of light at a dielectric interface gives rise to forces due to changes in the photon momentum1. At the microscopic level, these forces are sufficient to trap and rotate microscopic objects2,3. Such forces may have a profound impact in the emergent area of microfluidics, where there is the desire to process minimal amounts of analyte. This places stringent criteria on the ability to pump, move and mix small volumes of fluid, which will require the use of micro-components and their controlled actuation4,5,6,7. We demonstrate the modelling, fabrication and rotation of microgears based on the principle of form birefringence. Using a geometric anisotropy (a one-dimensional photonic crystal etched into the microgear), we can fabricate microgears of known birefringence, which may be readily rotated by manipulating the input polarization in a standard optical trap. This methodology offers a new and powerful mechanism for generating a wide range of microfabricated machines, such as micropumps, that may be driven by purely optical control.
TL;DR: An ambient temperature stationary "pump" is reported that generates a proton concentration gradient through the bipolar electrochemical decomposition of hydrogen peroxide on patterned silver-gold surfaces that drives convective fluid flow and pattern formation of colloidal tracer particles at the microscopic level.
Abstract: As innovations continue to be made in the fields of microfluidics and the colloidal assembly, new strategies for moving particles and fluids may be needed. Heterogeneous catalysis provides means of locally converting the stored chemical energy of fuels to mechanical energy. We report an ambient temperature stationary “pump” that generates a proton concentration gradient through the bipolar electrochemical decomposition of hydrogen peroxide on patterned silver−gold surfaces. The resulting electric field drives convective fluid flow and pattern formation of colloidal tracer particles at the microscopic level by a combination of electroosmotic and electrophoretic forces.
TL;DR: In this article, a droplet-based micro oscillating-flow PCR chip was designed and fabricated by the silicon microfabrication technique and three different temperature zones, which were stable at denaturation, extension and annealing temperatures, were integrated with a single, simple and straight microchannel to form the chip's basic functional structure.
Abstract: Polymerase chain reactions (PCR), thermally activated chemical reactions which are widely used for nucleic acid amplification, have recently received much attention in microelectromechanical systems and micro total analysis systems because a wide variety of DNA/RNA molecules can be enriched by PCR for further analyses. In the present work, a droplet-based micro oscillating-flow PCR chip was designed and fabricated by the silicon microfabrication technique. Three different temperature zones, which were stable at denaturation, extension and annealing temperatures and isolated from each other by a thin-wall linkage, were integrated with a single, simple and straight microchannel to form the chip’s basic functional structure. The PCR mixture was injected into the chip as a single droplet and flowed through the three temperature zones in the main microchannel in an oscillating manner to achieve the temperature maintenance and transitions. The chip’s thermal performance was theoretically analyzed and numerically simulated. The results indicated that the time needed for the temperature of the droplet to change to the target value is less than 1 s, and the root mean square error of temperature is less than 0.2 ◦ C. A droplet of 1 µ lP CR mixture with standard HPV (Human Papilloma Virus)-DNA sample inside was amplified by the present chip and the results were analyzed by slab gel electrophoresis with separation of DNA markers in parallel. The electrophoresis results demonstrated that the micro oscillating-flow PCR chip successfully amplified the HPV-DNA, with a processing time of about 15 min which is significantly reduced compared to that for the conventional PCR instrument. (Some figures in this article are in colour only in the electronic version)
TL;DR: In this article, the SU-8 chips with enclosed microchannels and high density of fluidic inlets have been made in a three-layer process which involves SU 8 to SU 8 adhesive bonding and sacrificial etching.
Abstract: Free-standing SU-8 chips with enclosed microchannels and high density of fluidic inlets have been made in a three-layer process which involves SU-8 to SU-8 adhesive bonding and sacrificial etching. With this process we can fabricate microchannels with depths ranging from 10 to 500 μm, channel widths from 10 to 2000 μm and lengths up to 6 cm. The process is optimized with respect to SU-8 glass transition temperature. Thermal stresses and thickness non-uniformities of SU-8 are compensated by novel mask design features, the auxiliary moats. With these process innovations filling of microchannels can be prevented, non-bonded area is minimized and bonding yields are 90% for large-area microfluidic chips. We have released up to 100 mm in diameter sized microfluidic chips completely from carrier wafers. These free-standing SU-8 chips are mechanically strong and show consistent wetting and capillary filling with aqueous fluids. Fluidic inlets were made in SU-8 chips by adding one lithography step, eliminating through-wafer etching or drilling. In our process the inlet size and density is limited by lithography only.
TL;DR: This removable microfluidic system for performing microarray hybridization on glass slides is promising for molecular diagnostics and gene profiling and did not require any purification of target nucleic acids.
Abstract: Background: Current hybridization protocols on microarrays are slow and need skilled personnel. Microfluidics is an emerging science that enables the processing of minute volumes of liquids to perform chemical, biochemical, or enzymatic analyzes. The merging of microfluidics and microarray technologies constitutes an elegant solution that will automate and speed up microarray hybridization.
Methods: We developed a microfluidic flow cell consisting of a network of chambers and channels molded into a polydimethylsiloxane substrate. The substrate was aligned and reversibly bound to the microarray printed on a standard glass slide to form a functional microfluidic unit. The microfluidic units were placed on an engraved, disc-shaped support fixed on a rotational device. Centrifugal forces drove the sample and buffers directly onto the microarray surface.
Results: This microfluidic system increased the hybridization signal by ∼10fold compared with a passive system that made use of 10 times more sample. By means of a 15–min automated hybridization process, performed at room temperature, we demonstrated the discrimination of 4 clinically relevant Staphylococcus species that differ by as little as a single-nucleotide polymorphism. This process included hybridization, washing, rinsing, and drying steps and did not require any purification of target nucleic acids. This platform was sensitive enough to detect 10 PCR-amplified bacterial genomes.
Conclusion: This removable microfluidic system for performing microarray hybridization on glass slides is promising for molecular diagnostics and gene profiling.
TL;DR: This review will explore several state of the art methods and applications of introducing solid supports into chips including packing chips with beads, incorporating membranes into chips, creating supports using microfabrication, and fabricating gels and polymer monoliths within microfluidic channels.
Abstract: The development of micro analytical systems requires that fluids are able to interact with the surface of the microfluidic chip in order to perform analysis such as chromatography, solid phase extraction, and enzymatic digestion. These types of analyses are more efficient if there are solid supports within the microfluidic channels. In addition, solid supports within microfluidic chips are useful in producing devices with multiple functionalities. In recent years there have been many approaches introduced for incorporating solid supports within chips. This review will explore several state of the art methods and applications of introducing solid supports into chips. These include packing chips with beads, incorporating membranes into chips, creating supports using microfabrication, and fabricating gels and polymer monoliths within microfluidic channels.
TL;DR: In this paper, a step-and-repeat fabrication process called liquid-phase photopolymerization (LP/sup 3/) is used to construct Ni microstructures driven by an external rotating magnetic field to serve as microactuators in the devices.
Abstract: Programmable autonomous micromixers and micropumps have been designed and realized via a merger between MEMS and microfluidic tectonics (/spl mu/FT). Advantages leveraged from both fabrication platforms allow for relatively simple and rapid fabrication of these microfluidic components. Nickel (Ni) microstructures, driven by an external rotating magnetic field, are patterned in situ and serve as the microactuators in the devices. /spl mu/FT permits in situ patterning through the use of a step-and-repeat fabrication process known as liquid-phase photopolymerization (LP/sup 3/). LP/sup 3/ is a polymer-based fabrication process tool that offers additional fabrication materials, including responsive hydrogels that expand and contract under different stimuli. Using pH- and temperature-sensitive hydrogels as clutches, autonomous micromixers and micropumps have been fabricated and tested that perform as closed-loop microsystems. The step-and-repeat fabrication process allows pre-programming of the system, like a programmable read-only memory chip, to be sensitive to a desired stimulus. Different Ni blade designs, and pH-sensitive hydrogel geometries and dimensions have been designed and tested to better ascertain their effects on micromixing efficiency and response times of hydrogels (related to the autonomous functionality), respectively. Temperature-responsive hydrogels have allowed for development of temperature-sensitive micromixers and micropumps with applications in areas demanding temperature control. [1498].
TL;DR: In this paper, the interplay between channel geometry and ordered foam/emulsion structures can be used to process tiny amounts of gases or liquids in a highly reliable and efficient way.
TL;DR: Different actuation mechanisms for microfluidics-based biochips, as well as associated design automation trends and challenges are presented, and the underlying physical principles of eletrokinetics, electrohydrodynamics, and thermo-capillarity are discussed.
Abstract: Advances in microfluidics technology offer exciting possibilities in the realm of enzymatic analysis, DNA analysis, proteomic analysis involving proteins and peptides, immunoassays, implantable drug delivery devices, and environmental toxicity monitoring. Microfluidics-based biochips are therefore gaining popularity for clinical diagnostics and other laboratory procedures involving molecular biology. As more bioassays are executed concurrently on a biochip, system integration and design complexity are expected to increase dramatically. This paper presents different actuation mechanisms for microfluidics-based biochips, as well as associated design automation trends and challenges. The underlying physical principles of eletrokinetics, electrohydrodynamics, and thermo-capillarity are discussed. Next, the paper presents an overview of an integrated system-level design methodology that attempts to address key issues in the modeling, simulation, synthesis, testing and reconfiguration of digital microfluidics-based biochips. The top-down design automation will facilitate the integration of fluidic components with microelectronic component in next-generation system-on-chip designs.
TL;DR: In this article, a single pump pulling at the device outlet can be used to drive hydrodynamic focusing with not only excellent control over the focus width and stream velocity, but also with minimal sample consumption.
Abstract: Hydrodynamic focusing has proven to be a useful microfluidics technique for the study of systems under rapid mixing conditions. Most studies to date have used a “push” configuration, requiring multiple pumps or pressure sources that complicate implementation and limit applications in point-of-care environments. Here, we demonstrate a simplified hydrodynamic focusing approach, in which a single pump pulling at the device outlet can be used to drive hydrodynamic focusing with not only excellent control over the focus width and stream velocity, but also with minimal sample consumption. In this technique, flow can be either mechanically driven or induced simply through capillarity.
TL;DR: Use of the photomodification procedure coupled to microfluidics allowed for the rapid generation of medium-density DNA microarrays and the use of this procedure for screening multiple KRAS2 mutations possessing high diagnostic value for colorectal cancers.
TL;DR: This method achieves flow rates in the microchannels ranging from approximately 1.2 nL s (-1) to approximately 30 pL s(-1), and is able to keep 90% of a 0.6 microL solution placed in an open filling port for 60 min.
Abstract: This paper presents a method for programming the flow rate of liquids inside open microfluidic networks (MFNs). A MFN comprises a number of independent flow paths, each of which starts with an open filling port, has a sealed microchannel in which assays can be performed, and an open capillary pump (CP). The MFN is placed over Peltier elements and its flow paths initially fill owing to capillary forces when liquids are added to the filling ports. A cooling Peltier element underneath the filling ports dynamically prevents evaporation in all filling ports using the ambient temperature and relative humidity as inputs. Another Peltier element underneath the CPs heats the pumps thereby inducing evaporation in the CPs and setting the flow rate in the microchannels. This method achieves flow rates in the microchannels ranging from ∼1.2 nL s−1 to ∼30 pL s−1, and is able to keep 90% of a 0.6 µL solution placed in an open filling port for 60 min. This simple and efficient method should be applicable to numerous assays or chemical reactions that require small and precise flow of liquids and reagents inside microfluidics.
01 Jan 2005
TL;DR: In this article, Coplanar electrowetting and transport and mixing in an open microfluidic substrate have been demonstrated on a printed circuit board (PCB) and a microfluide substrate.
Abstract: We report three novel demonstrations: 1 Coplanar electrowetting 2 Electrowetting on a printed circuit board (PCB) and 3 Transport and mixing in an “open” microfluidic substrate Similar to “soft” lithography which enabled many researchers to easily prototype and experiment with continuous-flow microfluidics, this work allows researchers to easily experiment with discrete-flow microfluidics (digital microfluidics) The flexibility in design afforded by this coplanar and “open” structure facilitates novel applications, particularly in areas of clinical diagnostics and reconfigurable chip cooling Furthermore, it provides digital microfluidic systems with an inexpensive and rapid turn-around process
TL;DR: The improved capture kinetics, transfer efficiency, and single-base specificity enabled by microfluidics make the processor well-suited for performing larger-scale DNA computations.
Abstract: An integrated microfluidic processor is developed that performs molecular computations using single nucleotide polymorphisms (SNPs) as binary bits. A complete population of fluorescein-labeled DNA "answers" is synthesized containing three distinct polymorphic bases; the identity of each base (A or T) is used to encode the value of a binary bit (TRUE or FALSE). Computation and readout occur by hybridization to complementary capture DNA oligonucleotides bound to magnetic beads in the microfluidic device. Beads are loaded into sixteen capture chambers in the processor and suspended in place by an external magnetic field. Integrated microfluidic valves and pumps circulate the input DNA population through the bead suspensions. In this example, a program consisting of a series of capture/rinse/release steps is executed and the DNA molecules remaining at the end of the computation provide the solution to a three-variable, four-clause Boolean satisfiability problem. The improved capture kinetics, transfer efficiency, and single-base specificity enabled by microfluidics make our processor well-suited for performing larger-scale DNA computations.
TL;DR: In this paper, the micro impedance pump was constructed of a simple thin-walled tube coupled at either end to glass capillary tubing and actuated electromagnetically to drive flow.
Abstract: Over the past two decades, a variety of micropumps have been explored for various applications in microfluidics such as control of pico- and nanoliter flows for drug delivery as well as chemical mixing and analysis. We present the fabrication and preliminary experimental studies of flow performance on the micro impedance pump, a previously unexplored method of pumping fluid on the microscale. The micro impedance pump was constructed of a simple thin-walled tube coupled at either end to glass capillary tubing and actuated electromagnetically. Through the cumulative effects of wave propagation and reflection originating from an excitation located asymmetrically along the length of the elastic tube, a pressure head can be established to drive flow. Flow rates were observed to be reversible and highly dependent on the profile of the excitation. Micro impedance pump flow studies were conducted in open and closed circuit flow configurations. Maximum flow rates of 16 ml min-1 have been achieved under closed loop flow conditions with an elastic tube diameter of 2 mm. Two size scales with channel diameters of 2 mm and 250 µm were also examined in open circuit flow, resulting in flow rates of 191 µl min-1 and 17 µl min-1, respectively.