Solute dispersion in oscillating electro-osmotic flow with boundary mass exchange

Mass transfer in an oscillatory electro-osmotic flow (EOF) is theoretically studied, for the case of a cylindrical tube with a reactive wall. An expression for the dispersion coefficient, reflecting the time-averaged mass flux of an electrically neutral solute, is derived analytically. Under the influence of a reversible solute-wall mass exchange, the dispersion coefficient exhibits a complex dependence on the various parameters representing the effects of the electric double-layer thickness, oscillation frequency, solution transport properties, solute partitioning, and reaction kinetics. Our results suggest that, in the presence of a reversible mass exchange at the wall, an oscillatory EOF may be used for separation of species. It is found that optimal conditions for separation are achieved for a thin double-layer, where an inert solute, or one with slow exchange kinetics, experiences virtually no dispersion while the dispersion is maximized for the reactive solute exhibiting fast kinetics.     

Replication of high-aspect-ratio nanopillar array for biomimetic gecko foot-hair prototype by UV nano embossing with anodic aluminum oxide mold

In this paper, we present a simple and cost-effective replication method of high-aspect-ratio polymer nanopillar array as a biomimetic gecko’s foot hair prototype. A UV nano embossing process was applied for the replication of polymer nanopillar arrays. Highly ordered straight nanoporous AAO (anodic aluminum oxide) templates were utilized as reusable master molds. Densely arranged high-aspect-ratio nanopillar arrays have been successfully fabricated by means of the UV nano embossing process with the AAO mold. Pull-off force measurements were carried out to characterize the adhesive force of the replicated nanopillar arrays on the polymer substrates based on the force–distance curves obtained from the atomic force microscope (AFM) with a modified AFM cantilever. The force measurement results showed that the larger diameter and the taller height of the nanopillars result in the larger adhesive force.     

低电压芯片电泳过程中流场的模拟计算和分析

本文基于一种阵列电极的低工作电压电泳芯片分离模型,在其中微管道的电场模拟的基础上,结合微流体动力学特性,以分离管道侧壁排布电极并等间距施加电压,建立电泳芯片低工作电压分离过程的流场模型,利用CoventorWare软件分析单组分和双组分试样在微分离管道中流场的模拟,发现组分在常规电压和低工作电压两种分离模式下,其迁移速度近似相等;对于双组分,分离电压可大大降低同时,还可保证原来的分离度,低电压电泳过程中,工作电压可降低至30 V.证实了阵列电极和运动梯度场实现低电压电泳的可行性和有效性.     

电泳芯片分离指标的模拟分析

对电泳芯片中影响区带展宽的相关因素进行了分析，给出了分离综合效率的表达式，建立了分离指标的数学模型。以此为基础，结合实验条件，利用计算机对影响分离指标的相关因素进行了模拟分析。结果表明，以分离综合效率为分离指标，可以反映分离条件对理论塔板数和分离时间的综合影响，而且，以分离指标的模拟分析为依据，可望实现电泳芯片的优化设计，在满足分离的前提下尽快地完成样品的分离分析过程。     

A dielectrophoresis-based microdevice coated with nanostructured TiO2 for separation of particles and cells

In this study, we present a microdevice coated with titanium dioxide for cells and particles separation and handling. The microsystem consists of a pair of planar interdigitated gold micro-electrode arrays on a quartz substrate able to generate a traveling electric completed with a microfabricated three-dimensional glass structure for cell confinement. Dielectrophoretic forces were exploited for both vertical and lateral cell motions. In order to provide a biocompatible passivation layer to the electrodes a highly biocompatible nanostructured titanium dioxide film was deposited by supersonic cluster beam deposition (SCBD) on the electrode array. The dielectrophoretic effects of the chip were initially tested using polystyrene beads. To test the biocompatibility and capability of dielectrophoretic cell movement of the device, four cell lines (NIH3T3, SH-SY5Y, MDCK, and PC12) were used. Separation of beads from SH-SY5Y cells was also obtained.     

Electrokinetic transport and separation of droplets in a microchannel

This work presents theoretical, numerical and experimental investigations of electrokinetic transport and separation of droplets in a microchannel. A theoretical model is used to predict that, in case of micron-sized droplets transported by electro-osmotic flow, the drag force is dominant as compared to the dielectrophoretic force. Numerical simulations were performed to capture the transient electrokinetic motion of the droplets using a two-dimensional multi-physics model. The numerical model employs Navier–Stokes equations for the fluid flow and Laplace equation for the electric potential in an Arbitrary Lagrangian–Eulerian framework. A microfluidic chip was fabricated using micromilling followed by solvent-assisted bonding. Experiments were performed with oil-in-water droplets produced using a cross-junction structure and applying electric fields using two cylindrical electrodes located at both ends of a straight microchannel. Droplets of different sizes were produced by controlling the relative flow rates of the discrete and continuous phases and separated along the channel due to the competition between the hydrodynamic and electrical forces. The numerical predictions of the particle transport are in quantitative agreement with the experimental results. The work reported here can be useful for separation and probing of individual biological cells for lab-on-chip applications.     

Evolution of high-sensitivity microarray technology

Microarray technology is a multiplex analytical technique for the detection of many different analytes in a mixture of biomolecules. The detection limits for each of the analytes for which the array is designed depend on a multiplicity of reaction parameters, the array itself, and profoundly on the label and detection technology employed. Significant improvements in assay sensitivity have been achieved by optimizing all steps that affect the generation of signal and noise. Nanoparticle technology brings a new dimension to this technology by providing not only higher sensitivity but also improved specificity for hybridization-based microarray assay systems.     

Simulation-Based Analysis of Dielectrophoretic Field Flow Fractionation Devices

Simulation of microfluidic devices is very difficult due to the interaction and coupling between multiple energy domains. This article presents an innovative technique to simulate dielectrophoretic forces and laminar flows in microfluidic devices. Lab-on-a-chip systems, or biochips, are one of the fastest growing sectors in the life sciences industry. These systems employ miniaturization of biological separation and assay techniques to enable multiple, complex analyses on a single chip. Separation of micron-sized particles and cells is critical in many biochemical-analysis and high-throughput-screening applications. Field flow fractionation (FFF) using dielectrophoresis (DEP) is fast becoming an established methodology for sorting and manipulating particles and cells.     

基于虚拟仪器的电渗流检测系统的设计

为实现微流控芯片的高精度分析,设计了一种基于虚拟仪器的微通道电渗流检测系统.介绍了电渗流测定的常用方法及其优缺点,基于电流监测法原理设计了微通道电渗流检测系统的硬件结构,采用LabVIEW软件开发了人-机界面.并在不同电场强度作用下,完成了微通道电渗流的测定.实验表明:该设计的检测系统能很好地满足微通道内部电渗流检测的需求.     

Parallel trapping of single motile cells based on vibration-induced flow

We propose an on-chip cell manipulation method for trapping single motile cells in parallel. The proposed method traps large (\(\gtrsim \,50\,\upmu \hbox {m}\)) motile cells in parallel, which is difficult to achieve by conventional cell manipulation methods based on optical, acoustic, electric, or magnetic forces. The trapping method exploits the flow induced by applying a vibration to a microfluidic chip with microstructures on its surface. By applying a rectilinear vibration to a chip with pairs of micropillars, we can trap single motile cells within the local flow generated between the micropillars. Using the proposed method, we trapped single Euglena gracilis cells (of size 50–100 \(\upmu \hbox {m}\)) in parallel. Moreover, we evaluate the trapping performance for various micropillar array design parameters and the controllability of the trapping-flow velocity by varying the amplitude of the vibration. The proposed method was then demonstrated in a motility evaluation of motile cells. The demonstration confirms the potential of the proposed method in realizing high-throughput motility evaluations of single motile cells.     

High-Voltage Dielectrophoretic and Magnetophoretic Hybrid Integrated Circuit/Microfluidic Chip

A hybrid integrated circuit (IC)/microfluidic chip is presented that independently and simultaneously traps and moves microscopic objects suspended in fluid using both electric and magnetic fields. This hybrid chip controls the location of dielectric objects, such as living cells and drops of fluid, on a 60 $times$ 61 array of pixels that are $30 times 38 mu hbox{m}^{2}$ in size, each of which can be individually addressed with a 50-V peak-to-peak dc-to-10-MHz radio-frequency voltage. These high-voltage pixels produce electric fields above the chip's surface with a magnitude $vert vec{E}vert approx 1 hbox{V}/muhbox{m}$ , resulting in strong dielectrophoresis (DEP) forces $vert vec{F}_{ rm DEP}vert approx 1 hbox{nN}$. Underneath the array of DEP pixels, there is a magnetic matrix that consists of two perpendicular sets of 60 metal wires running across the chip. Each wire can be sourced with 120 mA to trap and move magnetically susceptible objects using magnetophoresis. The DEP pixel array and magnetic matrix can be used simultaneously to apply forces to microscopic objects, such as living cells or lipid vesicles, that are tagged with magnetic nanoparticles. The capabilities of the hybrid IC/microfluidic chip demonstrated in this paper provide important building blocks for a platform for biological and chemical applications. $hfill$[2009-0142]      

Particle separation in alternating-current electro-osmotic micropumps using field-flow fractionation

This work presents a novel method for continuous particle separation on the microscale by means of field-flow fractionation. It is based on the use of asymmetric interdigitated electrode arrays on the channel bottom, which induce an electro-osmotic channel flow when driven harmonically. Suspended particles are influenced by viscous fluid drag, sedimentation as well as by dielectrophoretic repulsion forces from the driving electrodes due to the emerging electric field. The significant dependance of the present forces on particle properties allows for separation with respect to particle density and size. This work analyzes electric and flow field by means of the finite element method and investigates the size and density dependent particle motion as a function of driving voltage and frequency of the electrode array. Matching these driving parameters permits the separation of sedimenting particles by their density independently from their size as well as the separation by size. Finally, channel designs are proposed which enable standard separation by means of selective particle mobility in the channel, separation in terms of opposing motion directions, as well as continuous lateral separation.     

Numerical investigation of AC electrokinetic virus trapping inside high ionic strength media

A numerical investigation of the mechanism by which viral particles suspended in physiologically relevant (i.e., high ionic strength) media can be electrokinetically sampled on a surface is presented. Specifically, sampling of virus from a droplet is taking place by means of a high frequency non-uniform electric field, generated by energized planar quadrupolar microelectrodes deposited on an oxidized silicon chip. The numerical simulations are based on experimental conditions applied in our previous work with vesicular stomatitis virus. A 3D computer model is used to yield the spatial profiles of electric field intensity, temperature, and fluid velocity inside the droplet, as well as the force balance on the virus. The results suggest that rapid virus sampling can be achieved by the synergistic action of dielectrophoresis and electrothermal fluid flow. Specifically, electrothermal fluid flow can be used to transport the virus from the bulk of a sample to the surface, where dielectrophoretic forces, which become significant only at very small length scales away from the surface, can cause its stable capture.     

Zone electrophoresis of proteins in poly(dimethylsiloxane) (PDMS) microchip coated with physically adsorbed amphiphilic phospholipid polymer

The zone electrophoresis of protein in poly(dimethylsiloxane) (PDMS) microchip coated with the physically adsorbed amphiphilic phospholipid polymer (PMMSi) was investigated. PMMSi was composed of 2-methacryloyloxyethyl phosphorylcholine (MPC) and 3-(methacryloyloxy) propyltris (trimethylsiloxy) silane (MPTSSi) units in a random fashion. The membrane of PMMSi can be formed on the PDMS surface by a simple and quick dip-coating method. The membrane showed high hydrophilicity and good stability in water, as determined by contact angle measurement, fourier-transformed infrared absorption by attenuated total reflection (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS) analysis. High suppression of protein adsorption to the PDMS surface and reduction in electroosmotic flow (EOF) were achieved by PMMSi coating due to an increase of hydrophilicity, and a decrease of the ζ-potential on the surface of PDMS. For zone electrophoresis, the PMMSi30 containing 30 % hydrophilic MPC was the most suitable molecular design in terms of the stability of the coated membrane on PDMS surface. The average value of EOF mobility of PDMS microchip coated with PMMSi30 was 1.4 × 10^?4 cm² V^?1 s^?1, and the RSD was 4.1 %. Zone electrophoresis of uranine was further demonstrated with high repeatability and reproducibility. Separation of two FITC-labeled proteins (BSA and insulin) was performed with high efficiency and resolution compared with non-treated PDMS microchip.     

线阵电极电泳芯片与单片机控制系统

介绍了用于生化分析的一种微全分析控制系统,包括电泳芯片的设计制作、微机控制系统以及初步实验结果。新型电泳芯片基于线性阵列电极,可灵活设定分离时间、长度、电压等电泳的各项条件,满足多种分离需求。以C8051F020单片机为控制核心,扩展出大量并行I/O口,并与高压系统实现良好的控制与衔接。突出了单片机系统的高度集成、低功耗、高扩展性等特点,给出了扩展大量I/O口并灵活控制多路高压器件的实例。     

Somatic and stem cell pairing and fusion using a microfluidic array device

There is considerable excitement about the prospect of tissue repair and renewal through cell replacement therapies. Nonetheless, many of these techniques may require the reprogramming of somatic and stem cells through cell fusion. Previous fusion methods often suffer from random cell contacts, poor fusion yields, or complexity of design. We have developed a simplified cell-electrofusion chip that possesses a dense microelectrode array, which enables the simultaneous pairing and electrofusion of thousands of cells by manipulation dielectrophoretic force and electroporation. Human embryonic kidney 293 (HEK293) cells, mouse fibroblasts (NIH3T3 cells), and mouse embryonic stem cells were arranged for cell fusion with the same and mixed cell type. The pairing efficiency for a 2-cell alignment of mixed cells was ~35%, and a fusion efficiency of ~46% in cell pairs was achieved. Significant cell death occurs with fusion voltages ?? 10 V, and electrofusion with our chip was achieved on a ~1000 V cm^?1 electric field strength induced by a low intensity voltages (9 V). Therefore, the chip used in this study provides a simple, low voltage alternative with sufficient throughput for hybrid cell experiments and somatic cell reprogramming research.     

Configuring a wafer-scale two-dimensional array of single-bitprocessors

An overview of the ELSA (European large SIMD array) project, which uses a two-level strategy to achieve defect tolerance for wafer-scale architectures implemented in silicon, is presented. The target architecture is a 2-D array of processing elements for low-level image processing. An array is divided into subarrays called chips. At the chip level, defect tolerance is proved by an extra column of PEs (processing element) and bypassing techniques. At the wafer level, a double-rail connection network is used to construct a target array of defect-free chips that is as large and as fast as possible. Its main advantage is being independent of chip defects, as it is controlled from the I/O pads. An algorithm for constructing an optimized two-dimensional array on a wafer containing a given number of defect-free PEs and connections, a method to program the switches for the target architecture found by the algorithm, and software for programming the switches using laser cuts are discussed     

集成惯性聚焦结构的介电泳微流控芯片的粒子连续分离

设计并制造了一种带有惯性聚焦结构的介电泳微流控芯片,以实现不同介电性质的粒子连续分离.采用MEMS工艺制作了介电泳微流控芯片:通道入口侧壁设置一对梯形结构使经过的粒子受惯性升力的作用聚焦到通道两侧;通道底部光刻一组夹角为90°的倾斜叉指电极产生非均匀电场,利用介电泳力和流体曳力的合力使通道两侧不同的粒子发生角度不同的偏转进入不同通道,从而实现分离.将酵母菌细胞和聚苯乙烯小球作为实验样本,分析了流速和交流电压对分离的影响,确定了二者分离的最优条件并进行分离.实验结果表明,将电导率为20μS/cm的样本溶液以5μL/min的流速注入到通道中,施加6 Vp-p、10 kHz的正弦信号,酵母菌细胞沿电极运动至夹角处后沿通道中心排出,聚苯乙烯小球沿通道两侧排出,成功实现分离,平均分离效率达92.8％、平均分离纯度达90.7％.     

Study of the effect of electric field and electroneutrality on transport of biomolecules in microreactors

In this article, the effect of electrophoresis on the transport of a sample (like biomolecules) in active microreactors is numerically investigated. Navier–Stokes equations are solved along with the equations of electrostatics, species mass transport in the buffer, and chemical reaction kinetics at reactive surfaces. Unlike previous studies, in which the effect of the charge of the sample molecules on the electric field has been neglected (i.e., the assumption of electroneutrality), here the space charge density is assumed to be nonzero and a function of biomolecule concentration. As a result, the governing equations become fully coupled. The validity of the assumption is examined against experimental results. Then, the effect of electroneutrality on the efficiency of the microreactor device is analyzed for the parallel plate open channel geometry, commonly used in biomolecule separation. It is shown that the electroneutrality assumption can drastically influence the final adsorbed concentration depending on the device configuration. Average adsorbed surface concentration and capture efficiency are compared as measures of the performance of the device for a wide range of physiochemical parameters. The sensitivity of the simulation with respect to the ionic concentration of the buffer is investigated. It is also discussed how the electric field and nonzero space charge density alter the bulk concentration profile and the velocity field inside the microreactor.     

A pair of parallel differential magnetic‐field probes with high measurement accuracy and high electric‐field suppression ratio

Magnetic‐field probes can be used for electromagnetic interference measurement of high‐speed circuits. The main magnetic probe performance includes sensitivity, spatial resolution, electric‐field suppression ratio (EFSR), and measurement accuracy. In this article, a pair of differential magnetic‐field probes is proposed to improve measurement accuracy without reducing sensitivity. The proposed differential probes consist of two asymmetric loop probes, which are designed in the same plane and separated by a row of periodic vias. The proposed differential probes are fabricated under PCB process. High accuracy can be achieved by measuring difference between outputs of the two probes. In addition, EFSR can be improved by size optimization of the differential magnetic‐field probes. Simulation and measurement results show the operating bandwidth is from 100 MHz to 12 GHz, the measurement error is 3.4% and the EFSR is about 40 dB. The proposed probes have higher measurement accuracy and higher EFSR than the conventional single probe, and larger operation bandwidth than the stacked differential probes.