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December 2009

Volume 3, Issue 4, partial issue

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Study on surface properties of PDMS microfluidic chips treated with albumin

Walter Schrott ,
Zdeněk Slouka ,
Petr Červenka ,
Jiří Ston ,
Marek Nebyla ,
Michal Přibyl ,
and Dalimil Šnita

Biomicrofluidics 3, 044101 (2009) (15 pages)

Online Publication Date: 12 October 2009

Full Text: Read Online | Download PDF (886 KB)

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Electrokinetic properties and morphology of PDMS microfluidic chips intended for bioassays are studied. The chips are fabricated by a casting method followed by polymerization bonding. Microchannels are coated with 1% solution of bovine serum albumin (BSA) in Tris buffer. Albumin passively adsorbs on the PDMS surface. Electrokinetic characteristics (electro-osmotic velocity, electro-osmotic mobility, and zeta potential) of the coated PDMS channels are experimentally determined as functions of the electric field strength and the characteristic electrolyte concentration. Atomic force microscopy (AFM) analysis of the surface reveals a “peak and ridge” structure of the protein layer and an imperfect substrate coating. On the basis of the AFM observation, several topologies of the BSA-PDMS surface are proposed. A nonslip mathematical model of the electro-osmotic flow is then numerically analyzed. It is found that the electrokinetic characteristics computed for a channel with the homogeneous distribution of a fixed electric charge do not fit the experimental data. Heterogeneous distribution of the fixed electric charge and the surface roughness is thus taken into account. When a flat PDMS surface with electric charge heterogeneities is considered, the numerical results are in very good agreement with our experimental data. An optimization analysis finally allowed the determination of the surface concentration of the electric charge and the degree of the PDMS surface coating. The obtained findings can be important for correct prediction and possibly for robust control of behavior of electrically driven PDMS microfluidic chips. The proposed method of the electro-osmotic flow analysis at surfaces with a heterogeneous distribution of the surface electric charge can also be exploited in the interpretation of experimental studies dealing with protein-solid phase interactions or substrate coatings.
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87.80.Ek Mechanical and micromechanical techniques
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
87.85.Ox Biomedical instrumentation and transducers, including micro-electro-mechanical systems (MEMS)
47.85.Np Fluidics

Concurrent droplet charging and sorting by electrostatic actuation

Byungwook Ahn ,
Kangsun Lee ,
Romain Louge ,
and Kwang Oh

Biomicrofluidics 3, 044102 (2009) (8 pages)

Online Publication Date: 13 October 2009

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This paper presents a droplet-based microfluidic device for concurrent droplet charging and sorting by electrostatic actuation. Water-in-oil droplets can be charged on generation by synchronized electrostatic actuation. Then, simultaneously, the precharged droplets can be electrostatically steered into any designated laminar streamline, thus they can be sorted into one of multiple sorting channels one by one in a controlled fashion. In this paper, we studied the size dependence of the water droplets under various relative flow rates of water and oil. We demonstrated the concurrent charging and sorting of up to 600 droplets/s by synchronized electrostatic actuation. Finally, we investigated optimized voltages for stable droplet charging and sorting. This is an essential enabling technology for fast, robust, and multiplexed sorting of microdroplets, and for the droplet-based microfluidic systems.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
87.80.Ek Mechanical and micromechanical techniques
47.55.D- Drops and bubbles
47.85.Np Fluidics

Design and optimization of a double-enzyme glucose assay in microfluidic lab-on-a-chip

Yegermal Atalay ,
Daan Witters ,
Steven Vermeir ,
Nicolas Vergauwe ,
Pieter Verboven ,
Bart Nicolaï ,
and Jeroen Lammertyn

Biomicrofluidics 3, 044103 (2009) (14 pages)

Online Publication Date: 19 October 2009

Full Text: Read Online | Download PDF (757 KB)

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An electrokinetic driven microfluidic lab-on-a-chip was developed for glucose quantification using double-enzyme assay. The enzymatic glucose assay involves the two-step oxidation of glucose, which was catalyzed by hexokinase and glucose-6-phosphate dehydrogenase, with the concomitant reduction of NADP+ to NADPH. A fluorescence microscopy setup was used to monitor the different processes (fluid flow and enzymatic reaction) in the microfluidic chip. A two-dimensional finite element model was applied to understand the different aspects of design and to improve the performance of the device without extensive prototyping. To our knowledge this is the first work to exploit numerical simulation for understanding a multisubstrate double-enzyme on-chip assay. The assay is very complex to implement in electrokinetically driven continuous system due to the involvement of many species, which has different transport velocity. With the help of numerical simulation, the design parameters, flow rate, enzyme concentration, and reactor length, were optimized. The results from the simulation were in close agreement with the experimental results. A linear relation exists for glucose concentrations from 0.01 to 0.10 g l−1. The reaction time and the amount of enzymes required were drastically reduced compared to off-chip microplate analysis.
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87.80.Ek Mechanical and micromechanical techniques
87.14.ej Enzymes
87.15.R- Reactions and kinetics
87.10.Kn Finite element calculations
07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Dielectrophoretic field-flow method for separating particle populations in a chip with asymmetric electrodes

Ciprian Iliescu ,
Guillaume Tresset ,
and Guolin Xu

Biomicrofluidics 3, 044104 (2009) (10 pages)

Online Publication Date: 21 October 2009

Full Text: Read Online | Download PDF (743 KB)

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This paper presents a field-flow method for separating particle populations in a dielectrophoretic (DEP) chip with asymmetric electrodes under continuous flow. The structure of the DEP device (with one thick electrode that defines the walls of the microfluidic channel and one thin electrode), as well as the fabrication and characterization of the device, was previously described. A characteristic of this structure is that it generates an increased gradient of electric field in the vertical plane that can levitate the particles experiencing negative DEP. The separation method consists of trapping one population to the bottom of the microfluidic channel using positive DEP, while the other population that exhibits negative DEP is levitated and flowed out. Viable and nonviable yeast cells were used for testing of the separation method.
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87.80.Ek Mechanical and micromechanical techniques
47.85.Np Fluidics
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
82.45.-h Electrochemistry and electrophoresis
87.15.Tt Electrophoresis
87.17.-d Cell processes

A microfluidic DNA computing processor for gene expression analysis and gene drug synthesis

Yu Zhang ,
Hao Yu ,
Jianhua Qin ,
and Bingcheng Lin

Biomicrofluidics 3, 044105 (2009) (8 pages)

Online Publication Date: 6 November 2009

Full Text: Read Online | Download PDF (533 KB)

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Boolean logic performs a logical operation on one or more logic input and produces a single logic output. Here, we describe a microfluidic DNA computing processor performing Boolean logic operations for gene expression analysis and gene drug synthesis. Multiple cancer-related genes were used as input molecules. Their expression levels were identified by interacting with the computing related DNA strands, which were designed according to the sequences of cancer-related genes and the suicide gene. When all the expressions of the cancer-related genes fit in with the diagnostic criteria, positive diagnosis would be confirmed and then a complete suicide gene (gene drug) could be synthesized as an output molecule. Microfluidic chip was employed as an effective platform to realize the computing process by integrating multistep biochemical reactions involving hybridization, displacement, denaturalization, and ligation. By combining the specific design of the computing related molecules and the integrated functions of the microfluidics, the microfluidic DNA computing processor is able to analyze the multiple gene expressions simultaneously and realize the corresponding gene drug synthesis with simplicity and fast speed, which demonstrates the potential of this platform for DNA computing in biomedical applications.
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82.39.Pj Nucleic acids, DNA and RNA bases
87.15.Qt Sequence analysis
87.80.St Genomic techniques
47.85.-g Applied fluid mechanics

Cascade optical chromatography for sample fractionation

Alex Terray ,
Joseph Taylor ,
and Sean Hart

Biomicrofluidics 3, 044106 (2009) (6 pages)

Online Publication Date: 16 November 2009

Full Text: Read Online | Download PDF (322 KB)

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Optical chromatography involves the elegant combination of opposing optical and fluid drag forces on colloidal samples within microfluidic environments to both measure analytical differences and fractionate injected samples. Particles that encounter the focused laser beam are trapped axially along the beam and are pushed upstream from the laser focal point to rest at a point where the optical and fluid forces on the particle balance. In our recent devices particles are pushed into a region of lower microfluidic flow, where they can be retained and fractionated. Because optical and fluid forces on a particle are sensitive to differences in the physical and chemical properties of a sample, separations are possible. An optical chromatography beam focused to completely fill a fluid channel is operated as an optically tunable filter for the separation of inorganic, polymeric, and biological particle samples. We demonstrate this technique coupled with an advanced microfluidic platform and show how it can be used as an effective method to fractionate particles from an injected multicomponent sample. Our advanced three-stage microfluidic design accommodates three lasers simultaneously to effectively create a sequential cascade optical chromatographic separation system.
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87.80.Ek Mechanical and micromechanical techniques
87.50.wf Biophysical mechanisms of interaction
42.62.Be Biological and medical applications

Development and fertility studies on post-bio-electrosprayed Drosophila melanogaster embryos

Pascal Joly ,
Barbara Jennings ,
and Suwan Jayasinghe

Biomicrofluidics 3, 044107 (2009) (8 pages)

Online Publication Date: 18 November 2009

Full Text: Read Online | Download PDF (413 KB)

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Bio-electrosprays (BESs) provide a means of precisely manipulating cells and thus have the potential for many clinical uses such as the generation of artificial tissues/organs. Previously we tested the biological safety of this technology with a variety of living cells and also embryos from the vertebrate model organisms Danio rerio (zebrafish) and Xenopus tropicalis (frog). However, the viability and fertility of the treated embryos could not be fully assessed due to animal licensing laws. Here we assay the viability and fertility of Drosophila melanogaster (fruit fly) embryos in conjunction with the bio-electrospray procedure. Bio-electrosprayed Drosophila embryos developed into fully fertile adult flies that were indistinguishable from wild-type. Thus, we demonstrate that the bio-electrospray procedure does not induce genetic or physical damage that significantly affects the development or fertility of a multicellular organism. This study along with our previous investigations demonstrates the potential of this approach to be developed for the precise manipulation of sensitive biological materials.
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87.80.Fe Micromanipulation of biological structures
87.85.jc Electrical, thermal, and mechanical properties of biological matter
87.18.-h Biological complexity
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