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Showing papers on "Microfluidics published in 2002"


Journal ArticleDOI
TL;DR: In this article, the authors present a review of the book.http://www.reviewreviews.com/reviews/book-reviews-of-the-book
Abstract: Review

2,157 citations


Journal ArticleDOI
TL;DR: The focus of this review is microscale phenomena and the use of the physics of the scale to create devices and systems that provide functionality useful to the life sciences.
Abstract: ■ Abstract Fluid flow at the microscale exhibits unique phenomena that can be leveraged to fabricate devices and components capable of performing functions useful for biological studies. The physics of importance to microfluidics are reviewed. Common methods of fabricating microfluidic devices and systems are described. Components, including valves, mixers, and pumps, capable of controlling fluid flow by utilizing the physics of the microscale are presented. Techniques for sensing flow characteristics are described and examples of devices and systems that perform bioanalysis are presented. The focus of this review is microscale phenomena and the use of the physics of the scale to create devices and systems that provide functionality useful to the life sciences.

1,721 citations


Journal ArticleDOI
TL;DR: In this paper, an alternative approach to microfluidics based upon the micromanipulation of discrete droplets of aqueous electrolyte by electrowetting is reported.
Abstract: The serviceability of microfluidics-based instrumentation including ‘lab-on-a-chip’ systems critically depends on control of fluid motion. We are reporting here an alternative approach to microfluidics based upon the micromanipulation of discrete droplets of aqueous electrolyte by electrowetting. Using a simple open structure, consisting of two sets of opposing planar electrodes fabricated on glass substrates, positional and formational control of microdroplets ranging in size from several nanoliters to several microliters has been demonstrated at voltages between 15–100 V. Since there are no permanent channels or structures between the plates, the system is highly flexible and reconfigurable. Droplet transport is rapid and efficient with average velocities exceeding 10 cm s−1 having been observed. The dependence of the velocity on voltage is roughly independent of the droplet size within certain limits, thus the smallest droplets studied (∼3 nl) could be transported over 1000 times their length per second. Formation, mixing, and splitting of microdroplets was also demonstrated using the same microactuator structures. Thus, electrowetting provides a means to achieve high levels of functional integration and flexibility for microfluidic systems.

1,078 citations


Book
01 Jan 2002
TL;DR: In conclusion, microfluidics for Life Sciences and Chemistry Characterization Techniques for Microfluidic should be used for both internal and external flow control of fluid Mechanics in Micro Scale.
Abstract: Introduction Fluid Mechanics in Micro Scale Microtechnologies for Microfluidics Microfluidics for External Flow Control Microfluidics for Internal Flow Control Microfluidics for Life Sciences and Chemistry Characterization Techniques for Microfluidics

1,013 citations


Journal ArticleDOI
01 Jan 2002
TL;DR: Electrowetting and electrowetting-on-dielectric (EWOD) as discussed by the authors can control the wettability of liquids on solid surfaces using electric potential, which can be applied to microfluidic devices.
Abstract: This paper deals with electrowetting (EW) and electrowetting-on-dielectric (EWOD) principles applied to microfluidic devices. EW and EWOD are principles that can control wettability of liquids on solid surfaces using electric potential. While EW is controlling wettability of a certain electrolyte on a metal electrode by varying electric energy across the electrical double layer (EDL), EWOD applies to virtually any aqueous liquid by varying electric energy across the thin dielectric film between the liquid and conducting substrate. These driving mechanisms have many advantages. By electrically changing the wettability of each of the electrode patterns on a surface, a liquid on these electrodes can be shaped and driven along the active electrodes, making microfluidics extremely simple both for device fabrication and operation. It is also worth noting that, driven by surface tension, the mechanism becomes more effective as the size of the device becomes smaller. This paper describes fundamental concepts and the proof-of-concept experiments, modeling and design, microfabrication processes, and initial testing results for the microfluidic devices based on the EW and EWOD principles.

643 citations


Journal ArticleDOI
TL;DR: This work developed a scheme for metering fluids on the picoliter scale that is scalable to highly integrated parallel architectures and is independent of the properties of the working fluid, and demonstrates that diffraction-quality crystals may be grown and harvested from such nanoliter-volume reactions.
Abstract: Producing robust and scalable fluid metering in a microfluidic device is a challenging problem. We developed a scheme for metering fluids on the picoliter scale that is scalable to highly integrated parallel architectures and is independent of the properties of the working fluid. We demonstrated the power of this method by fabricating and testing a microfluidic chip for rapid screening of protein crystallization conditions, a major hurdle in structural biology efforts. The chip has 480 active valves and performs 144 parallel reactions, each of which uses only 10 nl of protein sample. The properties of microfluidic mixing allow an efficient kinetic trajectory for crystallization, and the microfluidic device outperforms conventional techniques by detecting more crystallization conditions while using 2 orders of magnitude less protein sample. We demonstrate that diffraction-quality crystals may be grown and harvested from such nanoliter-volume reactions.

586 citations


Journal ArticleDOI
TL;DR: Comparisons regarding pump size, flow rate, and backpressure will help readers to decide their proper design before starting a microfluidics project.
Abstract: Microfluidics has emerged from the MEMS-technology as an important research field and a promising market. We give an overview on one of the most important microfluidic components: the micropump. In the last decade, various micropumps have been developed. There are only a few review papers on microfluidic devices and none of them were dedicated only to micropumps. This review paper outlines systematically the pump principles and their realization with MEMS-technology. Comparisons regarding pump size, flow rate, and backpressure will help readers to decide their proper design before starting a microfluidics project. Different pump principles are compared graphically and discussed in terms of their advantages and disadvantages for particular applications

566 citations


Journal ArticleDOI
Teruo Fujii1
TL;DR: Fundamentals of PDMS-based microfluidic devices and their functions are described as well as the experimental results, where microreactors, microchips for capillary gel electrophoresis, and hydrophobic vent valves are successfully fabricated and operated.

479 citations


Journal ArticleDOI
TL;DR: The thermal diffusion constant D(T)=0.4x10(-8) cm(2)/s K for DNA is quantified for the first time and offers a new approach to biological microfluidics and replicating systems in prebiotic evolution.
Abstract: Thermophoresis depletes DNA from a heated spot. We quantify for the first time the thermal diffusion constant D(T)=0.4x10(-8) cm(2)/s K for DNA, using fluorescent dyes and laser heating. For 5 kB DNA we extrapolate a 1000-fold depletion from a temperature difference of 50 K. Surprisingly, convection generated by the same heating can turn the depletion into trapping of DNA. Trapped DNA can form point geometries 20 microm in diameter with more than 1000-fold enhanced concentrations. The accumulation is driven only by temperature gradients and offers a new approach to biological microfluidics and replicating systems in prebiotic evolution.

368 citations


Journal ArticleDOI
TL;DR: The fabrication of fluidic channels with dimensions smaller than 1 microm is described and characterized in respect to their use for detection of individual DNA molecules and the distribution and relative proportions of the individual fragments can be deduced from a single experiment.
Abstract: The fabrication of fluidic channels with dimensions smaller than 1 μm is described and characterized in respect to their use for detection of individual DNA molecules. The sacrificial layer technique is used to fabricate these devices as it provides CMOS-compatible materials exhibiting low fluorescence background. It also allows creating microfluidics circuitry of submicrometer dimensions with great control. The small dimensions facilitate single molecule detection and minimize events of simultaneous passage of more than one molecule through the measurement volume. The behavior of DNA molecules inside these channels under an applied electrical field was first studied by fluorescence correlation spectroscopy using M13 double-stranded DNA. A linear relationship between the flow speed and applied electric field across the channel was observed. Speeds as high as 5 mm/s were reached, corresponding to only a few milliseconds of analysis time per molecule. The channels were then used to characterize a mixture of...

245 citations


Journal ArticleDOI
TL;DR: Two methods for measuring the efficiency of DEP for trapping DNA molecules as well as a set of quantitative measurements of the effects of strand length, buffer composition, and frequency of the applied electric field are presented.
Abstract: Under suitable conditions, a DNA molecule in solution will develop a strong electric dipole moment. This induced dipole allows the molecule to be manipulated with field gradients, in a phenomenon known as dielectrophoresis (DEP). Pure dielectrophoretic motion of DNA requires alternate current (AC) electric fields to suppress the electrophoretic effect of the molecules net charge. In this paper, we present two methods for measuring the efficiency of DEP for trapping DNA molecules as well as a set of quantitative measurements of the effects of strand length, buffer composition, and frequency of the applied electric field. A simple configuration of electrodes in combination with a microfluidic flow chamber is shown to increase the concentration of DNA in solution by at least 60-fold. These results should prove useful in designing practical microfluidic devices employing this phenomenon either for separation or concentration of DNA.

Journal ArticleDOI
TL;DR: To direct liquid flow inside microchannels, surface free energies were patterned by use of self-assembled monolayers (SAMs) in combination with either multistream laminar flow or photolithography, showing that aqueous liquids flow only along the hydrophilic pathways when the pressure is maintained below a critical value.
Abstract: To direct liquid flow inside microchannels, surface free energies were patterned by use of self-assembled monolayers (SAMs) in combination with either multistream laminar flow or photolithography. For the photolithographic method, two photocleavable SAMs were designed and synthesized. Carboxylic acid-terminated monolayers were obtained by photodeprotection, which was confirmed by contact angle and X-ray photoelectron spectroscopy. Using either of these patterning methods, we show that aqueous liquids flow only along the hydrophilic pathways when the pressure is maintained below a critical value; the liquids are referred to as being confined by virtual walls. Several principles of liquid flow in surface-patterned channels were derived analytically and verified experimentally. These principles include the maximum pressure that virtual walls can withstand, the critical width of the hydrophilic pathway that can support spontaneous flow, the smallest width of the liquid streams under an external pressure, the ...

Journal ArticleDOI
TL;DR: In this paper, the authors describe the fabrication of flexible, polymeric 3D microfluidic systems with integrated check valves (flap and diaphragm valves) and a pump by stacking patterned poly(dimethylsiloxane) (PDMS) layers containing microchannels and vias.
Abstract: This paper describes the fabrication of flexible, polymeric 3-dimensional microfluidic systems with integrated check valves (flap and diaphragm valves) and a pump by stacking patterned poly(dimethylsiloxane) (PDMS) layers containing microchannels and vias. We describe this procedure for fabricating, manipulating, and bonding of PDMS membranes and bas-relief plates into multilayer microfluidic devices. The fabrication and demonstration of integrated check valves and a pump in a prototype polymer 3-dimensional microfluidic system is a step toward practical realization of all-polymer, flexible, low-cost, disposable microfluidic devices for biochemical applications.

Journal ArticleDOI
TL;DR: A microchip-based flow confinement method for rapid delivery of small sample volumes to sensor surfaces is described, and with the faster binding, sample consumption was reduced by 96% compared to conventional whole-channel sample delivery.
Abstract: A microchip-based flow confinement method for rapid delivery of small sample volumes to sensor surfaces is described. For flow confinement, a sample flow is joined with a perpendicular makeup flow of water or sample medium. Under laminar flow conditions, the makeup flow confines the sample into a thin layer above the sensing area and increases its velocity. This can benefit mass transport limited processes such as DNA hybridization or heterogeneous immunoassays. For proof of concept, this method was applied to a high-affinity immunoassay with excess capture antibody. Rabbit IgG was immobilized onto a silicon nitride waveguide. Cy5-labeled anti-rabbit IgG was hydrodynamically pumped over the immobilized zone through an attached 3D-PDMS flow cell with 20-μm-deep microchannels. The degree of confinement was adjusted through the volume flow rate of the confining flow. Evanescent field-based fluorescence detection enabled monitoring of the binding event. Assays were allowed to reach equilibrium to enable senso...

Proceedings ArticleDOI
07 Aug 2002
TL;DR: In this paper, the authors reported a dramatic reduction of liquid droplet flow resistance by engineering the surfaces into nanomechanical hydrophobic structures that show a contact angle over 175/spl deg.
Abstract: This paper reports a dramatic reduction of liquid droplet flow resistance by engineering the surfaces into nanomechanical hydrophobic structures that show a contact angle over 175/spl deg/. Flow resistances of droplets on open surfaces as well as in confined microchannels (between surfaces) have been measured with significant reduction of flow resistance (over 99% and over 95%, respectively) compared with a surface of the same material.

Patent
07 Feb 2002
TL;DR: In this article, a three-dimensional microfluidic device (100) formed from a plurality of substantially planar layers (101, 102, 103) sealed together is disclosed.
Abstract: A three-dimensional microfluidic device (100) formed from a plurality of substantially planar layers (101, 102, 103) sealed together is disclosed.

Proceedings ArticleDOI
07 Aug 2002
TL;DR: In this article, an electrowetting-on-dielectric (EWOD) actuation was demonstrated to improve the performance of dye-mixing using convolutions generated by discrete droplet flow.
Abstract: Enhancement of mixing using electrowetting-on-dielectric (EWOD) actuation is demonstrated. Exponential improvement over simple diffusion is theorized, based on convolutions generated by discrete droplet flow. The relationship between particle size, distance diffused, and diffusion time is studied. An improvement of 50 times over simple diffusion is experimentally shown, using a simple dye-mixing experiment.

Journal ArticleDOI
TL;DR: The photopolymerization of plugs containing different DNA probe sequences in one microfluidic channel is demonstrated, thereby enabling the selective detection of multiple DNA targets in one electrophoretic pathway.
Abstract: Acrylamide-modified DNA probes are immobilized in polycarbonate microfluidic channels via photopolymerization in a polyacrylamide matrix. The resulting polymeric, hydrogel plugs are porous under electrophoretic conditions and hybridize with fluorescently tagged complementary DNA. The double-stranded DNA can be chemically denatured, and the chip may be reused with a new analytical sample. Conditions for photopolymerization, hybridization, and denaturation are discussed. We also demonstrate the photopolymerization of plugs containing different DNA probe sequences in one microfluidic channel, thereby enabling the selective detection of multiple DNA targets in one electrophoretic pathway.

Journal ArticleDOI
TL;DR: In this article, a flow cytometer that uses an air-liquid two-phase microfluidic system to produce a focused high-speed liquid sample stream of particles and cells is described.
Abstract: This paper describes a disposable flow cytometer that uses an air-liquid two-phase microfluidic system to produce a focused high-speed liquid sample stream of particles and cells The susceptibility of thin liquid columns to instabilities may suggest that focusing of sample liquids with streams of air would be difficult The design of channel geometry, control of flow rates, and use of appropriate surface chemistries on the channel walls, however, enabled the generation of thin (15–100 μm) and partially bounded sample streams that were stable and suitable for rapid cell analysis Using an inverted epi-fluorescence microscope with a photo-multiplier tube, we demonstrated that the system is capable of counting the number of beads and C2C12 myoblast cells The effects of different flow rates and surface chemistries of the channel walls on the air-liquid two-phase flows were characterized using optical and confocal microscopy Use of air instead of liquids as a sheath fluid eliminates the need for large sheath liquid reservoirs, and reduces the volume and weight requirements The low manufacturing cost and high volumetric efficiency make the air-sheath flow cytometer attractive for use as a stand-alone device or as an integrated component of bio-artificial hybrid microsystems


Journal ArticleDOI
TL;DR: The possibilities of accelerating the hybridization process by using microfluidic channels made of polycarbonate, optionally with an integrated pump, and using an eSensor electrochemical DNA detection platform to investigate hybridization kinetics are examined.

Patent
28 Jan 2002
TL;DR: An apparatus and method for performing nucleic acid (DNA and/or RNA) sequencing on a single molecule is described in this article, where the genetic sequence information is obtained by probing through a DNA or RNA molecule base by base at nanometer scale as though looking through a strip of movie film.
Abstract: An apparatus and method for performing nucleic acid (DNA and/or RNA) sequencing on a single molecule The genetic sequence information is obtained by probing through a DNA or RNA molecule base by base at nanometer scale as though looking through a strip of movie film This DNA sequencing nanotechnology has the theoretical capability of performing DNA sequencing at a maximal rate of about 1,000,000 bases per second This enhanced performance is made possible by a series of innovations including: novel applications of a fine-tuned nanometer gap for passage of a single DNA or RNA molecule; thin layer microfluidics for sample loading and delivery; and programmable electric fields for precise control of DNA or RNA movement Detection methods include nanoelectrode-gated tunneling current measurements, dielectric molecular characterization, and atomic force microscopy/electrostatic force microscopy (AFM/EFM) probing for nanoscale reading of the nucleic acid sequences

BookDOI
01 Jan 2002
TL;DR: In this paper, Lim et al. present a review of the literature on Micropumps and present a model of the Actuator Unit and the Outlet Valve, as well as a development of Slip Model and Slip-Corrected Reynolds Equation for Gas Lubrication in Magnetic Storage Device.
Abstract: List of Contributors. Foreword. Preface. Acknowledgements. Part I: 1. Literature Review for Micropumps. 1.1. Origins of Micropump Research. 1.2. Mechanical Micropumps. 1.3. Non-mechanical Micropumps. 1.4. Motivation. 2. Design Rules for Micropumps. 2.1. Preliminary Design. 2.2. Compression Ratio. 2.3. Criterion for Switching of Valve. 2.4. Criterion for Self-priming Capability. 2.5. Criterion for Bubble Tolerance. 3. Modelling and Simulation. 3.1. Background of Microfluidics Systems Modelling. 3.2. Governing Equation for Micro-pumps. 3.3. Modelling of the Actuator Unit. 3.4. Modelling of the Inlet Valve. 3.5. Modelling of the Outlet Valve. 3.6. System Model of Proposed Micro-pump. 4. Process Development and Fabrication. 4.1. Bulk Silicon Micromachining. 4.2. Process Flow. 5. Verification and Testing. 5.1. Experimental Set-up. 5.2. Piezoelectric Actuator Unit Model Verification. 5.3. Preliminary Functional Tests. 5.4. Conclusions And Recommendations. References. Appendices: Appendix A. Appendix B. Appendix C. Appendix D. Part II: 6. Development of Integrated Microfluidic Devices for Genetic Analysis R.H. Liu, P. Grodzinski. 7. Microfluidic Devices on Printed Circuit Board S. Richter, Nam-Trung Nguyen, A. Wego, L. Pagel. 8. Nano and Micro Channel Flows of Bio-Molecular Suspension Fan Xijun, Nhan Phan-Thien, Ng Teng Yong, Wu Xuhong, Xu Diao. 9. Transport of Liquid in Rectangular Micro-Channels by Electroosmotic Pumping Chun Yang. 10. A Development of Slip Model and Slip-Corrected Reynolds Equation for Gas Lubrication in Magnetic Storage Device E. Yin-Kwee Ng, Ningyu Liu, Xiaohai Mao. 11. Short Notes on Particle Image Velocimetry for Micro/Nano Fluidic Measurements Chee Yen Lim, F.E.H. Tay. Index.

Journal ArticleDOI
TL;DR: In addition to bioactive fluid dispensing, ink-jet based microdispensing allows integration of features (electronic, photonic, sensing, structural, etc.) that are not possible, or very difficult, with traditional photolithographic-based MEMS fabrication methods.
Abstract: Applications of microfluidics and MEMS (micro-electromechanical systems) technology are emerging in many areas of biological and life sciences. Non-contact microdispensing systems for accurate, high-throughput deposition of bioactive fluids can be an enabling technology for these applications. In addition to bioactive fluid dispensing, ink-jet based microdispensing allows integration of features (electronic, photonic, sensing, structural, etc.) that are not possible, or very difficult, with traditional photolithographic-based MEMS fabrication methods. Our single fluid and mutlifluid (MatrixJet™) piezoelectric microdispensers have been used for spot synthesis of peptides, production of microspheres to deliver drugs/biological materials, microprinting of biodegradable polymers for cell proliferation in tissue engineering requirements, and spot deposition for DNA, diagnostic immunoassay, antibody and protein arrays. We have created optical elements, sensors, and electrical interconnects by microdeposition of polymers and metal alloys. We have also demonstrated the integration of a reverse phase microcolumn within a piezoelectric dispenser for use in the fractionation of peptides for mass spectrometer analysis.

Journal ArticleDOI
TL;DR: In this article, the authors describe a hybrid fluidics platform for a chip-based biosensor system that combines high-performance microfluidics components with powerful, yet compact, millimeter-scale pump and valve actuators.
Abstract: We describe the engineering of a hybrid fluidics platform for a chip-based biosensor system that combines high-performance microfluidics components with powerful, yet compact, millimeter-scale pump and valve actuators. The microfluidics system includes channels, valveless diffuser-based pumps, and pinch-valves that are cast into a poly(dimethylsiloxane) (PDMS) membrane and packaged along with the sensor chip into a palm-sized plastic cartridge. The microfluidics are driven by pump and valve actuators contained in an external unit (with a volume ~30 cm3) that interfaces kinematically with the PDMS microelements on the cartridge. The pump actuator is a simple-lever, flexure-hinge displacement amplifier that increases the motion of a piezoelectric stack. The valve actuators are an array of cantilevers operated by shape memory alloy wires. All components can be fabricated without the need for complex lithography or micromachining, and can be used with fluids containing micron-sized particulates. Prototypes have been modeled and tested to ensure the delivery of microliter volumes of fluid and the even dispersion of reagents over the chip sensing elements. With this hybrid approach to the fluidics system, the biochemical assay benefits from the many advantages of microfluidics yet we avoid the complexity and unknown reliability of immature microactuator technologies.

Journal ArticleDOI
TL;DR: In this paper, an approach for using electrowetting actuation in recirculating fluidic channels to achieve dynamic tuning of optical fiber structures was developed, where electrically controlled and fully reversible motion of the fluids and lubricants in these channels alters the refractive index profile experienced by the optical waveguide modes of the fiber.
Abstract: We have developed an approach for using electrowetting actuation in recirculating fluidic channels to achieve dynamic tuning of optical fiber structures. The electrically controlled and fully reversible motion of the fluids and lubricants in these channels alters the refractive index profile experienced by the optical waveguide modes of the fiber. When combined with in-fiber gratings and etched fibers, this fluidic system yields dynamically adjustable narrow and broadband fiber filters, respectively. The nonmechanical operation of these systems, their ability to support switching speeds on the order of milliseconds, and their excellent optical characteristics indicate a promising potential for electrowetting-actuated fluidic tuning in optical fiber devices and other photonic components.

Journal ArticleDOI
TL;DR: Capillary electrophoresis was found to be instrumental in measuring fine physicochemical parameters pertaining to DNA polyelectrolytes, such as their free mobility and their translational diffusion coefficients.
Abstract: A number of recent developments in DNA analysis by capillary electrophoresis are here reviewed. They include capillary arrays for fast, parallel DNA sequencing as well as microfabricated capillary arrays. Microfluidic chips for DNA sizing and quantitation are also covered, as well as microdevices containing arrays of regular obstacles acting as size-separators during DNA migration. Screening of DNA point mutations by two much improved techniques is also reported: in one case, such mutations are detected (but only on relative short, ca. 60-70 base-long fragments) by free electrophoresis in rather acidic (pH ca. 3) buffers; in the case of single-strand chain polymorphism, an improved technique is described based on near-neutral pH buffers with mixtures of Tris/MES cations/zwitterions. When studying the behavior of inorganic and organic cations in the Debye-Huckel layer of DNA, it was found that the latter (especially a large number of Good's buffers and other zwitterions, such as His) would bind to the DNA filament not only via charge interaction, but also via additional bonds, notably hydrogen bonds, thus altering the electrophoretic (and possibly the biological) behavior of DNA molecules. However, whether or not borate ions would bind to DNA remains still an unsettled question. Finally, capillary electrophoresis was found to be instrumental in measuring fine physicochemical parameters pertaining to DNA polyelectrolytes, such as their free mobility and their translational diffusion coefficients.

Journal ArticleDOI
TL;DR: This work demonstrates the first instance of a microfluidic-based analysis system with detection based on ion-selective optode membranes monitored with fluorescence transduction.
Abstract: The development of an integrated analysis system for small ions based on ion-selective optodes and centrifugal microfluidics is reported. The performance of this system was evaluated through five-point calibration plots for two types of optode membranes, one being cation-selective and the other anion-selective, which were incorporated into a microfluidics platform on which fluid motion is induced via angular rotation. Additionally, the application of the microfluidic platform to ion analysis is studied via a two-point calibration protocol used to quantify an unknown sample. Calibrant solutions are delivered from reservoirs fabricated onto the platform to a measuring area that contains the optode membrane, with a change in membrane fluorescence being monitored. This work demonstrates the first instance of a microfluidic-based analysis system with detection based on ion-selective optode membranes monitored with fluorescence transduction. Furthermore, in addition to employing a standard excitation source where a fiber-optic probe is coupled to a tungsten-halogen lamp, laser diodes such as those employed in portable CD/DVD players were studied as excitation sources to enhance the observed fluorescence signals.


Journal ArticleDOI
TL;DR: In this paper, the fabrication of microfluidic devices for bio-molecule separation using an array of well-defined nanostructures is described, using epifluorescence microscopy, using a fluorescein solution to track fluid penetration inside the high density nanostructure region.