Versatile method for electroosmotic flow measurements in microchip electrophoresis (original) (raw)
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Analytical Chemistry, 2001
The electroosmotic flow in laminated excimer laserablated microchannels has been studied as a function of the depth of the rectangular channels, and particular emphasis has been given to the difference in the -potentials between the lamination layer and the ablated substrate. Experimental electroosmotic flow follows the tendency predicted by a recently published model. The -potentials of lamination and ablated surfaces were determined for poly(ethylene terephthalate) and poly-(carbonate) substrates by fitting the experimental data with a numerical implementation of this model. In the experimentally investigated range of channel cross sections, a linear fit to the data gives a good approximation of the -potentials for both materials. Moreover, a flow injection analysis of fluorescein dye has been performed to show the severe loss in numbers of theoretical plates, caused by Taylor dispersion, when such microchannels, dedicated to microcapillary electrophoresis, are used.
Instrumentation design for hydrodynamic sample injection in microchip electrophoresis: A review
ELECTROPHORESIS, 2012
Reproducible and representative sample injection in microchip electrophoresis has been a bottleneck for quantitative analytical applications. Electrokinetic sample injection is the most used because it is easy to perform. However, this injection method is usually affected by sample composition and the bias effect. On the other hand, these drawbacks are overcome by the hydrodynamic (HD) sample injection, although this injection mode requires HD flow control. This review gives an overview of the basic principles, the instrumentation designs, and the performance of HD sample injection systems for microchip electrophoresis.
ELECTROPHORESIS, 2008
The effect of successive multiple ionic layer (SMIL) coatings on the velocity and direction of EOF and the separation efficiency for PDMS electrophoresis microchips was studied using different polymer structures and deposition conditions. To date, the majority of SMIL studies have used traditional CE and fused-silica capillaries. EOF was measured as a function of polymer structure and number of layers, in one case using the same anionic polymer and varying the cationic polymer and in the second case using the same cationic polymer and varying the anionic polymer. In both situations, the EOF direction reversed with each additional deposited polymer layer. The absolute EOF magnitude, however, did not vary significantly with layer number or polymer structure. Next, different coatings were used to compare separation efficiencies on native and SMIL-coated PDMS microchips. For native PDMS microchips, the average separation efficiency was 4105 6 1540 theoretical plates. The addition of two layers of polymer increased the separation efficiency anywhere from two-to five-fold, depending on the polymer structure. A maximum separation efficiency of 12 880 6 1050 theoretical plates was achieved for SMIL coatings of polybrene (cationic) and dextran sulfate (anionic) polymers after deposition of six total layers. It was also noted that coating improved run-to-run consistency of the peaks as noted by a reduction of the RSD of the EOF and separation efficiency. This study shows that the use of polyelectrolyte coatings, irrespective of the polymer structure, generates a consistent EOF in the current experiments and dramatically improves the separation efficiency when compared to unmodified PDMS microchips.
Journal of the Brazilian Chemical Society, 2011
A instrumentação para a determinação fotométrica do fluxo eletrosmótico (EOF) em dispositivos microfluídicos é descrita neste trabalho. A instrumentação é baseada em componentes acessíveis e consiste em um microscópio trinocular e no fotodiodo integrado OPT101. Um diodo emissor de luz (LED) de alta intensidade foi utilizado como fonte de radiação. Para as determinações foram utilizadas soluções aquosas dos corantes azul patente V e azul de metileno. O sistema foi utilizado no monitoramento do EOF em microdispositivos de poli(dimetilsiloxano) (PDMS) e híbridos de toner/vidro. As mobilidades do EOF determinadas em pH 7,0 foram (5,75 ± 0,01)10 -4 cm 2 V -1 s -1 e (3,2 ± 0,1)10 -4 cm 2 V -1 s -1 para os dispositivos de toner/vidro e PDMS, respectivamente. Medidas reprodutíveis foram obtidas em todos os experimentos, levando a uma alta precisão na determinação. O método proposto foi comparado com o método tradicional de determinação do EOF que envolve a medida da corrente nos microcanais.
On the surface modification of microchannels for microcapillary electrophoresis chips
This paper presents systematic investigation of the microchannel surface properties in microCE chips. Three popular materials for microCE chips, polydimethylsiloxane (PDMS), quartz, and glass, are used. The zeta potentials of these microchannels are calculated by measuring the EOF velocity to evaluate the surface properties after surface modification. The hydrophobic PDMS is usually plasma-treated for microCE applications. In this study, a new method using a high-throughput atmospheric plasma generator is adopted to treat the PDMS surface under atmospheric conditions. In this approach, the cost and time for surface treatment can be significantly reduced compared with the conventional vacuum plasma generator method. Experimental results indicate that new functional groups could be formed on the PDMS surface after treatment , resulting in a change in the surface property. The time-dependent surface property of the plasma-treated PDMS is then measured in terms of the zeta potential. Results show that the surface property will reach a stable condition after 1 h of plasma treatment. For glass CE chips, two new methods for changing the microchannel surface properties are developed. Instead of using complicated and time-consuming chemical silanization procedures for CE channel surface modification, two simple and reliable methods utilizing organic-based spin-on-glass and water-soluble acrylic resin are reported. The proposed method provides a fast batch process for controlling the surface properties of glass-based CE channels. The proposed methods are evaluated using fX-174 DNA maker separation. The experimental data show that the surface property is modified and separation efficiency greatly improved. In addition, the long-term stability of both coatings is verified in this study. The methods proposed in this study show potential as an excellent solution for glass-based microCE chip surface modification.
Journal of Micromechanics and Microengineering, 2004
This paper reports low-leakage injection techniques to deliver sample plugs within double-T-form electrophoresis microchips. Experimental and numerical investigations are used to predict and evaluate the leakage behavior during electrokinetic driving of the sample plugs. The principal material transport mechanisms including traditional cross-form, electro-floating, diffusion sampling injection techniques are discussed in this study. A simple and precise double-L injection technique that employs electrokinetic manipulations to avoid sample leakage within the microchip is also reported. The method needs only one electrical control point during injection and separation, so the control system can be smaller and cheaper. Experimental and numerical results show the proposed injection technique is able to reduce sample leakage significantly. No leakage happens after 16 sample injections using the double-L injection method while leakage usually happens using the traditional cross-form injection technique. The double-L injection technique proposed in this study has a great potential for use in high-precision analysis applications utilizing chip-based capillary electrophoresis.
Design and optimization of on-chip capillary electrophoresis
Electrophoresis, 2002
We present a systematic, experimentally validated method of designing electrokinetic injections for on-chip capillary electrophoresis applications. This method can be used to predict point-wise and charge-coupled device (CCD)-imaged electropherograms using estimates of species mobilities, diffusivities and initial sample plug parameters. A simple Taylor dispersion model is used to characterize electrophoretic separations in terms of resolution and signal-to-noise ratio (SNR). Detection convolutions using Gaussian and Boxcar detector response functions are used to relate optimal conditions for resolution and signal as a function of relevant system parameters including electroosmotic mobility, sample injection length, detector length scale, and the length-to-detector. Analytical solutions show a tradeoff between signal-to-noise ratio and resolution with respect to dimensionless injection width and length to the detector. In contrast, there is no tradeoff with respect to the Peclet number as increases in Peclet number favor both SNR and separation solution (R). We validate our model with quantitative epifluorescence visualizations of electrophoretic separation experiments in a simple cross channel microchip. For the pure advection regime of dispersion, we use numerical simulations of the transient convective diffusion processes associated with electrokinetics together with an optimization algorithm to design a voltage control scheme which produces an injection plug that has minimal advective dispersion. We also validate this optimal injection scheme using fluorescence visualizations. These validations show that optimized voltage scheme produces injections with a standard deviation less than one-fifth of the width of the microchannel.
Numerical simulation of electrokinetic injection techniques in capillary electrophoresis microchips
ELECTROPHORESIS, 2005
The effective design and control of a capillary electrophoresis (CE) microchip requires a thorough understanding of the electrokinetic transport phenomena associated with its microfluidic injection system. The present study utilizes a numerical simulation approach to investigate these electrokinetic transport processes and to study the control parameters of the injection process. Injection systems with a variety of different configurations are designed and tested, including the cross-form, T-form, double-Tform, variable-volume focused flow cross-form, and variable-volume triple-T-form configuration. Each injection system cycles through a predetermined series of steps in which the magnitudes and distributions of the applied electric field are precisely manipulated in order to effectuate a virtual valve. This study investigates the sample leakage effect associated with each of the injection configurations and applies the double-L, pullback, and focusing injection techniques to minimize the sample leakage effect. The injection methods presented in this paper have the exciting potential for use in high-quality, high-throughput chemical analysis applications and throughout the micro-total-analysis systems field.
Model and verification of electrokinetic flow and transport in a micro-electrophoresis device
Lab on a Chip, 2005
We investigate the electrokinetic flow and transport within a micro-electrophoresis device. A mathematical model is set up, which allows to perform two-dimensional, time-dependent finite-element simulations. The model reflects the dominant features of the system, namely electroosmosis, electrophoresis, externally-applied electrical potentials, and equilibrium chemistry. For the solution of the model equations we rely on numerical simulations of the core region, while the immediate wall region is treated analytically at leading order. This avoids extreme refinements of the numerical grid within the EDL. An asymptotic matching of both solutions and subsequent superposition, nevertheless, provides an approximation for the solution in the entire domain. The results of the simulations are verified against experimental observation and show good agreement.