Publications by authors named "Johan G Bomer"

19 Publications

  • Page 1 of 1

Reduction of Taylor-Aris dispersion by lateral mixing for chromatographic applications.

Lab Chip 2020 11 25;20(21):3938-3947. Epub 2020 Sep 25.

μFlow Group, Department of Chemical Engineering, Vrije Universiteit Brussel, Pleinlaan 2, 1050, Brussels, Belgium.

Chromatographic columns are suffering from Taylor-Aris dispersion, especially for slowly diffusing molecules such as proteins. Since downscaling the channel size to reduce Taylor-Aris dispersion meets fundamental pressure limitations, new strategies are needed to further improve chromatography beyond its current limits. In this work we demonstrate a method to reduce Taylor-Aris dispersion by lateral mixing in a newly designed silicon AC-electroosmotic flow mixer. We obtained a reduction in κ by a factor of three in a 40 μm × 20 μm microchannel, corresponding to a plate height gain of 2 to 3 under unretained conditions at low to high Pe values. We also demonstrate an improvement of a reverse-phase chromatographic separation of coumarins.
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http://dx.doi.org/10.1039/d0lc00773kDOI Listing
November 2020

Plasmonic Bubble Nucleation and Growth in Water: Effect of Dissolved Air.

J Phys Chem C Nanomater Interfaces 2019 Sep 28;123(38):23586-23593. Epub 2019 Aug 28.

Physics of Fluids, Max Planck Center Twente for Complex Fluid Dynamics and J.M. Burgers Centre for Fluid Mechanics, MESA+ Institute, Physics of Interfaces and Nanomaterials, MESA+ Institute, TechMed Centre, and BIOS Lab-on-a-Chip, MESA+ Institute, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands.

Under continuous laser irradiation, noble metal nanoparticles immersed in water can quickly heat up, leading to the nucleation of so-called plasmonic bubbles. In this work, we want to further understand the bubble nucleation and growth mechanism. In particular, we quantitatively study the effect of the amount of dissolved air on the bubble nucleation and growth dynamics, both for the initial giant bubble, which forms shortly after switching on the laser and is mainly composed of vapor, and for the final life phase of the bubble, during which it mainly contains air expelled from water. We found that the bubble nucleation temperature depends on the gas concentration: the higher the gas concentration, the lower the bubble nucleation temperature. Also, the long-term diffusion-dominated bubble growth is governed by the gas concentration. The radius of the bubbles grows as () ∝ for air-equilibrated and air-oversaturated water. In contrast, in partially degassed water, the growth is much slower since, even for the highest temperature we achieve, the water remains undersaturated.
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http://dx.doi.org/10.1021/acs.jpcc.9b05374DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6768170PMC
September 2019

Wafer-scale fabrication of high-quality tunable gold nanogap arrays for surface-enhanced Raman scattering.

Nanoscale 2019 Jul 13;11(25):12152-12160. Epub 2019 Jun 13.

BIOS Lab-on-a-Chip Group, MESA+ Institute, Max Planck Center for Complex Fluid Dynamics, University of Twente, 7522 NB Enschede, The Netherlands.

We report a robust and high-yield fabrication method for wafer-scale patterning of high-quality arrays of dense gold nanogaps, combining displacement Talbot lithography based shrink-etching with dry etching, wet etching, and thin film deposition techniques. By using the self-sharpening of <111>-oriented silicon crystal planes during the wet etching process, silicon structures with extremely smooth nanogaps are obtained. Subsequent conformal deposition of a silicon nitride layer and a gold layer results in dense arrays of narrow gold nanogaps. Using this method, we successfully fabricate high-quality Au nanogaps down to 10 nm over full wafer areas. Moreover, the gap spacing can be tuned by changing the thickness of deposited Au layers. Since the roughness of the template is minimized by the crystallographic etching of silicon, the roughness of the gold nanogaps depends almost exclusively on the roughness of the sputtered gold layers. Additionally, our fabricated Au nanogaps show a significant enhancement of surface-enhanced Raman scattering (SERS) signals of benzenethiol molecules chemisorbed on the structure surface, at an average enhancement factor up to 1.5 × 10.
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http://dx.doi.org/10.1039/c9nr02215eDOI Listing
July 2019

A miniaturized push-pull-perfusion probe for few-second sampling of neurotransmitters in the mouse brain.

Lab Chip 2019 04;19(8):1332-1343

BIOS - Microdevices for Chemical Analysis group, MESA+ Institute for Nanotechnology, Techmed Centre, University of Twente, Hallenweg 15, 7522 NH Enschede, The Netherlands.

Measuring biomolecule concentrations in the brain of living animals, in real time, is a challenging task, especially when detailed information at high temporal resolution is also required. Traditionally, microdialysis probes are used that generally have sampling areas in the order of about 1 mm2, and provide information on concentrations with a temporal resolution of at least several minutes. In this paper, we present a novel miniaturized push-pull perfusion sampling probe that uses an array of small 3 μm-wide sampling channels to sample neurotransmitters at a typical recovery rate of 61%, with a reduced risk of clogging. The added feature to segment the dialysate inside the probe into small water-in-decane droplets enables the detection of concentrations with a temporal resolution of a few seconds. Here we used the probe for in vivo recordings of neurotransmitter glutamate released upon electrical stimulation in the brain of a mouse to demonstrate the feasibility of the probe for real-time neurochemical brain analysis.
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http://dx.doi.org/10.1039/c8lc01137kDOI Listing
April 2019

Gradient in the electric field for particle position detection in microfluidic channels.

Lab Chip 2019 03;19(6):1054-1059

BIOS Lab on a Chip Group, MESA+ Institute for Nanotechnology, University of Twente, Drienerlolaan 5, Enschede, The Netherlands.

In this work, a new method to track particles in microfluidic channels is presented. Particle position tracking in microfluidic systems is crucial to characterize sorting systems or to improve the analysis of cells in impedance flow cytometry studies. By developing an electric field gradient in a two parallel electrode array the position of the particles can be tracked in one axis by impedance analysis. This method can track the particle's position at lower frequencies and measure the conductivity of the system at higher frequencies. A 3-D simulation was performed showing particle position detection and conductivity analysis. To experimentally validate the technique, a microfluidic chip that develops a gradient in the electric field was fabricated and used to detect the position of polystyrene particles in one axis and measure their conductivity at low and high frequencies, respectively.
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http://dx.doi.org/10.1039/c8lc01333kDOI Listing
March 2019

Integrated microfluidic biosensing platform for simultaneous confocal microscopy and electrophysiological measurements on bilayer lipid membranes and ion channels.

Electrophoresis 2018 02 21;39(3):496-503. Epub 2017 Dec 21.

BIOS, Lab on a chip Group, MESA+ Institute for Nanotechnology, MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, The Netherlands.

Combining high-resolution imaging and electrophysiological recordings is key for various types of experimentation on lipid bilayers and ion channels. Here, we propose an integrated biosensing platform consisting of a microfluidic cartridge and a dedicated chip-holder to conduct such dual measurements on suspended lipid bilayers, in a user-friendly manner. To illustrate the potential of the integrated platform, we characterize lipid bilayers in terms of thickness and fluidity while simultaneously monitoring single ion channel currents. For that purpose, POPC lipid bilayers are supplemented with a fluorescently-tagged phospholipid (NBD-PE, 1% mol) for Fluorescence Recovery After Photobleaching (FRAP) measurements and a model ion channel (gramicidin, 1 nM). These combined measurements reveal that NBD-PE has no effect on the lipid bilayer thickness while gramicidin induces thinning of the membrane. Furthermore, the presence of gramicidin does not alter the lipid bilayer fluidity. Surprisingly, in lipid bilayers supplemented with both probes, a reduction in gramicidin open probability and lifetime is observed compared to lipid bilayers with gramicidin only, suggesting an influence of NBD-PE on the gramicidin ion function. Altogether, our proposed microfluidic biosensing platform in combination with the herein presented multi-parametric measurement scheme paves the way to explore the interdependent relationship between lipid bilayer properties and ion channel function.
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http://dx.doi.org/10.1002/elps.201700346DOI Listing
February 2018

Exploiting biased reptation for continuous flow preparative DNA fractionation in a versatile microfluidic platform.

Microsyst Nanoeng 2017 22;3:17001. Epub 2017 May 22.

BIOS Lab-on-a-Chip Group, MESA+ Institute for Nanotechnology, MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, 7500 AE Enschede, The Netherlands.

A new approach is presented for preparative, continuous flow fractionation of sub-10-kbp DNA fragments, which exploits the variation in the field-dependent mobility of the DNA molecules based on their length. Orthogonally pulsed electric fields of significantly different magnitudes are applied to a microchip filled with a sieving matrix of 1.2% agarose gel. Using this method, we demonstrate a high-resolution separation of 0.5, 1, 2, 5, and 10 kbp DNA fragments within 2 min. During the separation, DNA fragments are also purified from other ionic species. Preparative fractionation of sub-10-kbp DNA molecules plays an important role in second-generation sequencing. The presented device performs rapid high-resolution fractionation and it can be reliably manufactured with simple microfabrication procedures.
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http://dx.doi.org/10.1038/micronano.2017.1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6444976PMC
May 2017

Spermometer: electrical characterization of single boar sperm motility.

Fertil Steril 2016 Sep 6;106(3):773-780.e6. Epub 2016 Jun 6.

BIOS - Lab on a Chip Group, MESA+ Institute for Nanotechnology and MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, the Netherlands; Department of Obstetrics and Gynaecology, Radboud University Nijmegen Medical Centre, Nijmegen, the Netherlands. Electronic address:

Objective: To study single sperm boar motility using electrical impedance measurements in a microfluidic system.

Design: Comparison of the optical data and electrical impedance data.

Setting: Research laboratory at a university.

Animal(s): Boar semen sample were used.

Intervention(s): A microfluidic system is developed that is able to spatially confine single boar sperm cells and allows noninvasive analysis of their motility on the single cell level. Using this system, the single sperm motility was affected by changing the temperature or adding chemical stimuli (caffeine). The retrieved electrical impedance and video data were processed using Matlab.

Main Outcome Measure(s): The sperm beat frequency and amplitude determined from the electrical impedance and video data.

Result(s): The electrically measured sperm beat frequency was verified by optical analysis and in correspondence. Furthermore the microfluidic platform allowed single sperm analysis by altering the sperm by temperature and chemical stimuli.

Conclusion(s): This platform could be exploited as a potential tool to study sperm cells on the single cell level and to perform advanced sperm selection for intracytoplasmic sperm injection (ICSI) applications.
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http://dx.doi.org/10.1016/j.fertnstert.2016.05.008DOI Listing
September 2016

Photopatterning of Hydrogel Microarrays in Closed Microchips.

Biomacromolecules 2015 Dec 19;16(12):3802-10. Epub 2015 Nov 19.

BIOS Lab-on-a-Chip Group, MESA+ Institute for Nanotechnology, MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente , Enschede, The Netherlands.

To date, optical lithography has been extensively used for in situ patterning of hydrogel structures in a scale range from hundreds of microns to a few millimeters. The two main limitations which prevent smaller feature sizes of hydrogel structures are (1) the upper glass layer of a microchip maintains a large spacing (typically 525 μm) between the photomask and hydrogel precursor, leading to diffraction of UV light at the edges of mask patterns, (2) diffusion of free radicals and monomers results in irregular polymerization near the illumination interface. In this work, we present a simple approach to enable the use of optical lithography to fabricate hydrogel arrays with a minimum feature size of 4 μm inside closed microchips. To achieve this, we combined two different techniques. First, the upper glass layer of the microchip was thinned by mechanical polishing to reduce the spacing between the photomask and hydrogel precursor, and thereby the diffraction of UV light at the edges of mask patterns. The polishing process reduces the upper layer thickness from ∼525 to ∼100 μm, and the mean surface roughness from 20 to 3 nm. Second, we developed an intermittent illumination technique consisting of short illumination periods followed by relatively longer dark periods, which decrease the diffusion of monomers. Combination of these two methods allows for fabrication of 0.4 × 10(6) sub-10 μm sized hydrogel patterns over large areas (cm(2)) with high reproducibility (∼98.5% patterning success). The patterning method is tested with two different types of photopolymerizing hydrogels: polyacrylamide and polyethylene glycol diacrylate. This method enables in situ fabrication of well-defined hydrogel patterns and presents a simple approach to fabricate 3-D hydrogel matrices for biomolecule separation, biosensing, tissue engineering, and immobilized protein microarray applications.
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http://dx.doi.org/10.1021/acs.biomac.5b01104DOI Listing
December 2015

Large scale patterning of hydrogel microarrays using capillary pinning.

Lab Chip 2015 Feb;15(3):664-7

BIOS Lab-on-a-Chip Group, MESA+ Institute for Nanotechnology, MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, The Netherlands.

Capillary barriers provide a simple and elegant means for autonomous fluid-flow control in microfluidic systems. In this work, we report on the fabrication of periodic hydrogel microarrays in closed microfluidic systems using non-fluorescent capillary barriers. This design strategy enables the fabrication of picoliter-volume patterns of photopolymerized and thermo-gelling hydrogels without any defects and distortions.
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http://dx.doi.org/10.1039/c4lc01350fDOI Listing
February 2015

Wafer-scale fabrication of glass-FEP-glass microfluidic devices for lipid bilayer experiments.

Lab Chip 2014 Dec 6;14(23):4461-4. Epub 2014 Oct 6.

BIOS - Lab on a Chip group, MESA+ Institute for Nanotechnology, MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, The Netherlands.

We report a wafer-scale fabrication process for the production of glass-FEP-glass microdevices using UV-curable adhesive (NOA81) as gluing material, which is applied using a novel "spin & roll" approach. Devices are characterized for the uniformity of the gluing layer, presence of glue in the microchannels, and alignment precision. Experiments on lipid bilayers with electrophysiological recordings using a model pore-forming polypeptide are demonstrated.
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http://dx.doi.org/10.1039/c4lc00921eDOI Listing
December 2014

High yield, reproducible and quasi-automated bilayer formation in a microfluidic format.

Small 2013 Apr 9;9(7):1076-85. Epub 2012 Nov 9.

BIOS-Lab on a Chip Group, MESA+ Institute for Nanotechnology, University of Twente, Enschede, The Netherlands.

A microfluidic platform is reported for various experimentation schemes on cell membrane models and membrane proteins using a combination of electrical and optical measurements, including confocal microscopy. Bilayer lipid membranes (BLMs) are prepared in the device upon spontaneous and instantaneous thinning of the lipid solution in a 100-μm dry-etched aperture in a 12.5-μm thick Teflon foil. Using this quasi-automated approach, a remarkable 100% membrane formation yield is reached (including reflushing in 4% of the cases), and BLMs are stable for up to 36 h. Furthermore, the potential of this platform is demonstrated for (i) the in-depth characterization of BLMs comprising both synthetic and natural lipids (1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) and L-α-phosphatidylcholine (L-α-PC)/cholesterol, respectively) in terms of seal resistance, capacitance, surface area, specific capacitance, and membrane hydrophobic thickness; (ii) confocal microscopy imaging of phase separation in sphingomyelin/L-α-PC/cholesterol ternary membranes; (iii) electrical measurements of individual nanopores (α-hemolysin, gramicidin); and (iv) indirect assessment of the alteration of membrane properties upon exposure to chemical stimuli using the natural nanopore gramicidin as a sensor.
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http://dx.doi.org/10.1002/smll.201201821DOI Listing
April 2013

Microfluidic DNA fragmentation for on-chip genomic analysis.

Nanotechnology 2011 Dec 21;22(49):494013. Epub 2011 Nov 21.

BIOS/Lab-on-Chip Group, MESA + Institute for Nanotechnology, University of Twente, The Netherlands.

We report a high-throughput clog-free microfluidic deoxyribonucleic acid (DNA) fragmentation chip that is based on hydrodynamic shearing. Salmon sperm DNA has been reproducibly fragmented down to ∼ 5k bp fragment lengths by applying low hydraulic pressures (≤1 bar) across micromachined constrictions positioned in larger microfluidic channels that create point-sink flow with large velocity gradients near the constriction entrance. Long constrictions (100 µm) produce shorter fragment lengths compared to shorter constrictions (10 µm), while increasing the hydrodynamic pressure requirement. Sample recirculation (10 ×) in short constrictions reduces the mean fragment length and fragment length variation, and improves yield compared to single-pass experiments without increasing the hydrodynamic pressure.
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http://dx.doi.org/10.1088/0957-4484/22/49/494013DOI Listing
December 2011

Electrokinetic DNA transport in 20 nm-high nanoslits: evidence for movement through a wall-adsorbed.

Electrophoresis 2011 Sep 26;32(18):2402-9. Epub 2011 Aug 26.

Nanobioengineering Group, Institute for Bioengineering of Catalonia, Josep Samitier, Barcelona, Spain.

The electrokinetic transport behavior of λ-DNA (48 kbp) in 20 nm-high fused-silica nanoslits in the presence of short-chain PVP is investigated. Mobility and video data show a number of phenomena that are typical of DNA transport through gels or polymer solutions, thus indicative of rigid migration obstacles in the DNA pathway. Calculations show that a several nanometer thin layer of wall-adsorbed PVP ('nano-gel') can provide such a rigid obstacle matrix to the DNA. Such ultrathin wall-adsorbed polymer layers represent a new type of matrix for electrokinetic DNA separation.
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http://dx.doi.org/10.1002/elps.201100278DOI Listing
September 2011

Al2O3/silicon nanoISFET with near ideal nernstian response.

Nano Lett 2011 Jun 28;11(6):2334-41. Epub 2011 Apr 28.

BIOS Lab on a Chip Group, MESA+ Institute for Nanotechnology, University of Twente, Enschede, The Netherlands.

Nanoscale ISFET (ion sensitive field-effect transistor) pH sensors are presented that produce the well-known sub-nernstian pH-response for silicon dioxide (SiO(2)) surfaces and near ideal nernstian sensitivity for alumina (Al(2)O(3)) surfaces. Titration experiments of SiO(2) surfaces resulted in a varying pH sensitivity ∼20 mV/pH for pH near 2 and >45 mV/pH for pH > 5. Measured pH responses from titrations of thin (15 nm) atomic layer deposited (ALD) alumina (Al(2)O(3)) surfaces on the nanoISFETs resulted in near ideal nernstian pH sensitivity of 57.8 ± 1.2 mV/pH (pH range: 2-10; T = 22 °C) and temperature sensitivity of 0.19 mV/pH °C (22 °C ≤ T ≤ 40 °C). A comprehensive analytical model of the nanoISFET sensor, which is based on the combined Gouy-Chapman-Stern and Site-Binding (GCS-SB) model, accompanies the experimental results and an extracted ΔpK ≈ 1.5 from the measured responses further supports the near ideal nernstian pH sensitivity.
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http://dx.doi.org/10.1021/nl200623nDOI Listing
June 2011

A new floating electrode structure for generating homogeneous electrical fields in microfluidic channels.

Lab Chip 2011 Jun 31;11(12):1995-2001. Epub 2011 Jan 31.

BIOS-Lab on a Chip group, MESA+ Institute for Nanotechnology, University of Twente, P.O. box 217, 7500 AE Enschede, The Netherlands.

In this article a new parallel electrode structure in a microfluidic channel is described that makes use of a floating electrode to get a homogeneous electrical field. Compared to existing parallel electrode structures, the new structure has an easier production process and there is no need for an electrical connection to both sides of the microfluidic chip. With the new chip design, polystyrene beads suspended in background electrolyte have been detected using electrical impedance measurements. The results of electrical impedance changes caused by beads passing the electrodes are compared with results in a similar planar electrode configuration. It is shown that in the new configuration the coefficient of variation of the impedance changes is lower compared to the planar configuration (0.39 versus 0.56) and less dependent on the position of the beads passage in the channel as a result of the homogeneous electrical field. To our knowledge this is the first time that a floating electrode is used for the realization of a parallel electrode structure. The proposed production method for parallel electrodes in microfluidic channels can easily be applied to other applications.
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http://dx.doi.org/10.1039/c0lc00489hDOI Listing
June 2011

Electrokinetic label-free screening chip: a marriage of multiplexing and high throughput analysis using surface plasmon resonance imaging.

Lab Chip 2010 Apr 9;10(8):986-90. Epub 2010 Mar 9.

BIOS Lab-on-a-Chip Group, MESA+ Institute for Nanotechnology, University of Twente, Enschede, The Netherlands.

We present an electrokinetic label-free biomolecular screening chip (Glass/PDMS) to screen up to 10 samples simultaneously using surface plasmon resonance imaging (iSPR). This approach reduces the duration of an experiment when compared to conventional experimental methods. This new device offers a high degree of parallelization not only for analyte samples, but also for multiplex analyte interactions where up to 90 ligands are immobilized on the sensing surface. The proof of concept has been demonstrated with well-known biomolecular interactant pairs. The new chip can be used for high throughput screening applications and kinetics parameter extraction, simultaneously, of interactant-protein complex formation.
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http://dx.doi.org/10.1039/c000705fDOI Listing
April 2010

Top-down fabrication of sub-30 nm monocrystalline silicon nanowires using conventional microfabrication.

ACS Nano 2009 Nov;3(11):3485-92

BIOS Lab on a Chip Group, University of Twente, Enschede, The Netherlands.

We report a new low-cost top-down silicon nanowire fabrication technology requiring only conventional microfabrication processes including microlithography, oxidation, and wet anisotropic plane-dependent etching; high quality silicon nanowire arrays can be easily made in any conventional microfabrication facility without nanolithography or expensive equipment. Silicon nanowires with scalable lateral dimensions ranging from 200 nm down to 10-20 nm and lengths up to approximately 100 microm can be precisely formed with near-perfect monocrystalline cross sections, atomically smooth surfaces, and wafer-scale yields greater than 90% using a novel size reduction method where silicon nanowires can be controllably scaled to any dimension and doping concentration independent of large contacting regions from a continuous layer of crystalline silicon.
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http://dx.doi.org/10.1021/nn901220gDOI Listing
November 2009

Continuous flow microfluidic demixing of electrolytes by induced charge electrokinetics in structured electrode arrays.

Anal Chem 2006 Mar;78(5):1425-34

MESA Institute for Nanotechnology, BIOS/ Lab-on-a-Chip Group, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.

A continuous flow microfluidic demixing process is realized. It utilizes high external electrical fields that are applied over electrically floating noble metal electrodes in an otherwise straight microchannel. The process converts axial electrical potential gradients into lateral molecular selective transport via a structure oriented ensemble of numerous electrodes. While the individual electrodes locally modify the electrolyte distribution by nonlinear electrokinetic effects and concentration polarization, the directed orientation of the electrode array combines the individual polarization zones to a dedicated molecular enrichment against the generated concentration gradient. A homogeneously concentrated electrolyte can be separated into arbitrarily shaped laminae of increased and depleted concentration by the presented microfluidic demixer.
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http://dx.doi.org/10.1021/ac051615nDOI Listing
March 2006
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