Effects of Chip Geometries on Dielectrophoresis and Electrorotation Investigation

The electric fields employed for such work are generated using chips, such as planar linear interdigitated arrays or two parallel arrays. However, chip geometries usually affect the investigation of dielectrophoresis （DEP） and electrorotation （ER） significantly, and even may misdirect the theoretical prediction. In order to understand the electrodes geometries effect and provide a suitable range of parameters, three-dimensional simulations for the DEP and ER characterizations on the quadrupolar hyperbolical electrodes are carried out. Influences of the electrodes gaps, cell height, work region, energized voltage and frequencies for the DEP and ER manipulations are analyzed, and the analysis results show that the gaps of the electrodes and the cell height have enormous effects, but the work region is not so important. Moreover, depending on the theoretical analysis, ER experiments for polystyrene microspheres with the diameter of 20 ~m are carried out on two kinds of chips. The experimental results show that the microspheres rotate in the counter-field direction and the maximum rotation speed appears in the megahertz range. In addition, the experimental results are compared with the simulation results, showing that the three-dimensional simulations considering the chip geometries are more accurate than the two-dimensional predictions. This paper provides a new understanding for the theoretical predictions of DEP and ER manipulations, which decreases the difference of the theoretical and experimental results significantly, and will be significant for the lab chip research.

Separation and Manipulation of Rare-earth Oxide Particles by Dielectrophoresis

A challenge in chemical engineering is the separation and purification of rare-earth elements and their compounds. We report the design and manufacture of a dielectrophoresis(DEP) microchip of microelectrode arrays. This microchip device is constructed in order to use DEP to capture micro-particles of rare-earth oxides in petro-leum. Dielectrophoretic behavior of micro-particles of rare-earth oxides in oil media is explored. The dielectropho-retic effects of particles under different conditions are investigated. It is showed that the prepared microchip is suit-able for use in the investigation of dielectrophoretic responses of the rare-earth oxides in oil media. The factors such as frequency,particle size and valence of rare-earth metal are discussed. When the frequency is fixed,the transla-tion voltage decreases as particle size increases. Lower frequencies are more effective for manipulation of inorganic particles in oil media. Particles of the same rare-earth oxide with different size,as well as particles of different rare-earth oxides,are captured in different regions of the field by regulating DEP conditions. This may be a new method for separation and purification of particles of different rare-earth oxides,as well as classification of particles with different size.

Microwire formation based on dielectrophoresis of electroless gold plated polystyrene microspheres

Microspheres coated with a perfectly conductive surface have many advantages in the applications of biosensors and micro-electromechanical systems. Polystyrene microspheres with the diameter of 10 μm were coated with a 50 nmthick gold layer using an electroless gold plating approach. Dielectrophoresis （DEP） for bare microspheres and shelled microspheres was theoretically analysed and the real part of the Clausius Mossotti factor was calculated for the two kinds of microspheres. The experiments on the dielectrophoretic characterisation of the uncoated polystyrene microspheres and gold coated polystyrene microspheres （GCPMs） were carried out. Experimental results showed that the gold coated polystyrene microspheres were only acted by a positive dielectrophoretic force when the frequency was below 40M Hz, while the uncoated polystyrene microspheres were governed by a negative dielectrophoretic force in this frequency range. The gold coated polystyrene microspheres were exploited to form the rnicrowire automatically according to their stable dielectrophoretic and electric characterisations.

Continuous Separation of Multiple Size Microparticles using Alternating Current Dielectrophoresis in Microfluidic Device with Acupuncture Needle Electrodes

The need to continuously separate multiple microparticles is required for the recent development of lab-on-chip technology. Dielectrophoresis（DEP）-based separation device is extensively used in kinds of microfluidic applications. However, such conventional DEP-based device is relatively complicated and difficult for fabrication. A concise microfluidic device is presented for effective continuous separation of multiple size particle mixtures. A pair of acupuncture needle electrodes are creatively employed and embedded in a PDMS（poly-dimethylsiloxane） hurdle for generating non-uniform electric field thereby achieving a continuous DEP separation. The separation mechanism is that the incoming particle samples with different sizes experience different negative DEP（n DEP） forces and then they can be transported into different downstream outlets. The DEP characterizations of particles are calculated, and their trajectories are numerically predicted by considering the combined action of the incoming laminar flow and the n DEP force field for guiding the separation experiments. The device performance is verified by successfully separating a three-sized particle mixture, including polystyrene microspheres with diameters of 3 μm, 10 μm and 25 μm. The separation purity is below 70% when the flow rate ratio is less than 3.5 or more than 5.1, while the separation purity can be up to more than 90% when the flow rate ratio is between 3.5 and 5.1 and meanwhile ensure the voltage output falls in between 120 V and 150 V. Such simple DEP-based separation device has extensive applications in future microfluidic systems.

Different localized states of travelling-wave convection in a rectangular container

We have performed numerical simulations of localized travelling-wave convection in a binary fluid mixture heated from below in a long rectangular container. Calculations are carried out in a vertical cross section of the rolls perpendic- ular to their axes. For a negative enough separation ratio, two types of quite different confined states were documented by applying different control processes. One branch of localized travelling waves survives only in a very narrow band within subcritical regime, while another branch straddles the onset of convection existing both in subcritical and super- critical regions. We elucidated that concentration field and its current are key to understand how confined convection is sustained when conductive state is absolutely unstable, The weak structures in the conducting region are demonstrated too.

Improvement Design of Biochip Towards High Stable Bioparticle Detection Utilizing Dielectrophoresis Impedance Measurement

Dielectrophoresis impedance measurement(DEPIM)is a powerful tool for bioparticle detection due to its advantages of high efficiency,label-free and low costs.However,the strong electric field may decrease the viability of the bioparticle,thus leading to instability of impedance measurement.A new design of biochip is presented with high stable bioparticle detection capabilities by using both negative dielectrophoresis(nDEP)and traveling wave dielectrophoresis(twDEP).In the biochip,a spiral electrode is arranged on the top of channel,while a detector is arranged on the bottom of the channel.The influence factors on the DEP force and twDEP force are investigated by using the basic principle of DEP,based on which,the relationship between Clausius-Mossotti(CM)factor and the frequency of electric field is obtained.The two-dimensional model of the biochip is built by using Comsol Multiphysics.Electric potential distribution,force distribution and particle trajectory in the channel are then obtained by using the simulation model.Finally,both the simulations and experiments are performed to demonstrate that the new biochip can enhance the detection efficiency and reduce the negative effects of electric field on the bioparticles.

Manipulation and Separation of Particles of Metal Oxides by Dielectrophoresis

With the development of nanotecbnology, the separation and manipulation of micro-nano-panicles have become a research focus in the field of nano-materials, nielectrophoresis（DEP） is a non-contact technology for the separation and manipulation of micro-nano-particles. Here is reported the design and fabrication of a DEP based microchip with microelectrode arrays for capturing micro-particles of inorganic oxides in petroleum. The DEP behavior of micro-particles of inorganic oxides in oil media was explored via this microchip. The microchip shows relatively a good DEP response to inorganic oxides in oil media. Furthermore, much more factors were explored such as fiequency（Hz）, and particle size（μm）, as well as metal valence. As a conclusion, the best frequency is 50 Hz. It is expected to capture panicles with different sizes or separate different oxide panicles by regulating DEP conditions. Thus, a new method could be established for the separation and purification panicles of different oxides, as well as the separation and manipulation of an oxide with different particle sizes.

Fabricating Nanogaps between Nanoelectrodes using Dielectrophoresis Technique for Molecular Fluorescence Enhancement

Here we demonstrate the fabrication of nanometer-sized gaps by assembling single coreshell nanoparticles between metallic nanoelectrodes. Protein coated SiO2@Au coreshell nanopar- tides arc synthesized and positioned between fluorescent molecules-covered electrodes in a controllable way using dielectrophoretic trapping, forming nanogaps sandwiched between nanoparticle and manoelectrodes. Preliminary photoluminescence measurements show that enhanced molecular fluorescence could be detected from the fluorescent molecules inside the nanogaps. These results pave the way for realizing electrically driven molecular fluorescence based on nanogap electrodes.

Particle captured by a field-modulating vortex through dielectrophoresis force

In microfluidic technology, dielectrophoresis(DEP) is commonly used to manipulate particles. In this work, the fluid–particle interactions in a microfluidic system are investigated numerically by a finite difference method(FDM) for electric field distribution and a lattice Boltzmann method(LBM) for the fluid flow. In this system, efficient particle manipulation may be realized by combining DEP and field-modulating vortex. The influence of the density(ρ_(p)), radius(γ), and initial position of the particle in the y direction(y_(p0)), and the slip velocity(u_(0)) on the particle manipulation are studied systematically. It is found that compared with the particle without action of DEP force, the particle subjected to a DEP force may be captured by the vortex over a wider range of parameters. In the y direction, as ρ_(p) or γ increases, the particle can be captured more easily by the vortex since it is subjected to a stronger DEP force. When u_(0) is low, particle is more likely to be captured due to the vortex–particle interaction. Furthermore, the flow field around the particle is analyzed to explore the underlying mechanism. The results obtained in the present study may provide theoretical support for engineering applications of field-controlled vortices to manipulate particles.

The Role of Electric Field and Ultrasonication in the Deposition and Alignment of Single-Walled Carbon Nanotube Networks Using Dielectrophoresis

The effects of electric field and ultrasonication on the deposition and alignment of single-walled carbon nanotubes (SWCNTs) across a 10 μm electrode gap have been studied. It was found that a frequency of ~1 MHz of the applied field yields the largest current independent of the magnitude of the voltage or the ultrasonication time of the sample. Increasing the ultrasonication time of a SWCNT solution changes the I-V characteristics of the deposited nanotubes from linear to nonlinear for all the voltages and frequencies of the applied field. Even in the absence of an electric field, SWCNTs bridged the electrode gap up to a critical sonication time which depends on the concentration of nanotubes in the solution.

Microchip Electrode Development for Traveling wave Dielectrophoresis of Non-Spherical Cell Suspensions

A microchip interdigitated electrode with a sequential signal generator has been developed for traveling wave dielectrophoresis (twDEP) of biological cell suspensions. The electrode was fabricated on a microscope glass slide and coated with a 0.5 μm thickness of gold through a sputtering technique which was designed for large-scale inductions of cells rather than for individual cells as in previous versions of our device. As designed for a representative cell size of 10 μm, the electrode array was 50 μm in width to allow large numbers (>106) of cells to be processed. The sequential signal generator produces an arbitrary AC quadrature-phase to generate traveling electric field for a microchip interdigitated electrode. Each phase signal can be automatically altered and alternated with the other phases within interval time of 0.01-30 seconds (controlled by programming). We demonstrate the system could be used to estimate the dielectric properties of the yeast Saccharomyces cerivisiae TISTR 5088, the green alga Tetraselmis sp. and human red blood cells (HRBCs) through curve-fitting of dielectro- phoretic velocities and critical frequencies.

Combining field-modulating electroosmotic vortex and insulating post to manipulate particles based on dielectrophoresis

The dielectrophoretic technology has been one of the most frequently applied microfluidic technologies to manipulate particles.The way of a combination of controlled electroosmotic micro-vortices and dielectrophoresis to manipulate particles of different sizes was proposed in our previous work.However,the thickness of the modulating electrode is neglected.In practice,when the thickness of the modulating electrode increases,the channel flux increases,while the ability of the vortex to capture the particles reduces.In this study,a new method combining the field-modulating electroosmotic vortex and the insulating post is proposed to improve the manipulating capability of the field-modulated electroosmotic vortex to particles.The results indicate that there are three great advantages as the insulating post is placed on the channel wall on the same side of the modulating electrode.First,the capturing ability of the vortex to particles is greater due to the reduction of channel flux and the squeezing effect.Second,the range of regulating channel flux to achieve the optimal separation is extended.Third,the separation efficiency improves since the perfect separation can be achieved at a higher flow rate.Furthermore,the effects of the location and the size of the insulating post on particle separation are analyzed in detail.The present work could provide the reference for the application of the DEP technology.

Attaching single carbon nanotube on tip's apex using dielectrophoresis of DC-pulse voltage

Single carbon nanotubes (CNTs) are candidates for a number of electronics and sensing applications, provided that single CNTs can be separated from a bundle of CNTs in suspension. Dielectrophoresis has recently been demonstrated as one route for the extraction of desired CNTs. However, previous methods using dielectrophoresis have found it difficult to extract single nanotubes from bundles of CNTs in solution. Here, we show that this restriction can be overcome by using pulsed DC voltage of an electric field, instead of regular AC and DC voltages.

Simulation Study on the Controllable Dielectrophoresis Parameters of Graphene

The method of using dielectrophoresis （DEP） to assemble graphene between micro-electrodes has been proven to be simple and efficient. We present an optimization method for the kinetic formula of graphene DEP, and discuss the simulation of the graphene assembly process based on the finite element method. The simulated results illustrate that the accelerated motion of graphene is in agreement with the distribution of the electric field squared gradient. We also conduct research on the controllable parameters of the DEP assembly such as the alternating current （AC） frequency, the shape of micro-electrodes, and the ratio of the gap between electrodes to the characteristic/geometric length of graphene （λ）. The simulations based on the Clausius-Mossotti factor reveal that both graphene velocity and direction are influenced by the AC frequency. When graphene is close to the electrodes, the shape of micro-electrodes will exert great influence on the velocity of graphene. Also, λ has a great influence on the velocity of graphene. Generally, the velocity of graphene would be greater when λ is in the range of 0.4 0.6. The study is of a theoretical guiding significance in improving the precision and efficiency of the graphene DEP assembly.

基于双柔性电极模拟叉指图案电极的液体介电泳研究

介电泳通过非均匀电场作用于介电液体内偶极子影响表面润湿性,实现液滴接触角可调,克服了电润湿效应的接触角饱和限制,但其驱动电极需图案化处理,难以实现实用的三维可调光学器件.本文采用外裹绝缘介电层且互不导通的双柔性电极缠绕于平板基底形成二维平面线墙,模拟叉指图案电极以驱动液体介电泳,给出了“液滴-叉指平面线墙”模型的接触角与电压理论关系.在0—250 V_(rms)电压范围内实验测量的接触角变化可达32°,符合上述理论关系,为构造液体介电泳三维可调光学器件提供了理论和实验基础.

工艺参数对浸没式直流介电泳辅助化学机械抛光蓝宝石晶片的影响

目的为了实现蓝宝石晶片的高效超光滑表面加工,提出浸没式直流介电泳辅助化学机械抛光方法,研究该方法对蓝宝石晶片的加工适应性。方法搭建了浸没式直流介电泳辅助化学机械抛光系统,通过单因素实验探究接入电压、工件及抛光盘转速、偏摆移动速度、抛光时间及抛光垫类型对蓝宝石晶片的加工效果,并深入分析负介电泳效应对CMP加工过程的影响。结果直流介电泳辅助CMP方法可以显著提高蓝宝石晶片的抛光效果,在2000V的接入电压下,化学机械抛光的材料去除率MRR提高了99.97%,达到了7.53nm/min,表面粗糙度Ra降低至2.51nm,工件表面划痕数量明显减少。工件及抛光盘转速、偏摆移动速度的提升都会使抛光MRR和Ra先升后降,带槽的抛光垫对介电泳效应控制磨料起促进作用。各个因素的影响对提高有效磨料数起交互作用,负介电泳效应促使磨料聚集在抛光垫表面,而工件与抛光垫的相对运动促使磨料更新循环。结论采用接入电压2000 V、工件及抛光盘转速80 r/min、偏摆速度60 r/min,在精抛垫下抛光蓝宝石晶片90 min,可以获得表面粗糙度Ra为0.953 nm的光滑表面。

针板结构极不均匀电场中气泡迁移特性与吸附静止状态的绝缘特性分析

以去离子水作为冷却介质的换流阀散热系统难以同时兼顾绝缘与散热性能,影响了系统的可靠运行。相变冷却技术凭借卓越的散热能力正在逐步应用于高压大功率电力电子器件的冷却,但液体电介质中的气泡有绝缘劣化的风险。为更好掌握相变冷却气泡在极不均匀电场中的迁移特性和绝缘特性,采用数值模拟的方法分析了气泡粒径、速度和电场强度这3个关键因素对气泡运动轨迹的影响;研究了进入低场区后不同接触角气泡,对绝缘子表面电场强度的影响。研究结果揭示了各因素对气泡运动轨迹的显著影响,加深了对相变冷却气泡迁移特性和绝缘特性的认知,对直流装备相变冷却的进一步应用具有重要参考价值。

基于介电电泳的微流控细胞分离芯片的研究进展

细胞分离技术是细胞分选和细胞种群纯化的重要手段,在生物、医学、农业、环境等许多领域都有重要的应用,是当前生化分析领域的国际研究热点。本文介绍了基于介电电泳的微流控细胞分离芯片的研究现状,阐述了介电电泳的工作原理,并依据细胞尺寸、电极形状、外加信号方式等影响细胞介电电泳的关键因素对不同类型的微流控细胞分离芯片进行了详细介绍,并对该技术的未来发展趋势做了展望。

交流电场强度对导线雾凇覆冰特性的影响

输电线路覆冰严重威胁着电力系统的安全,国内外对导线覆冰开展了大量研究,但绝大部分研究都没有考虑电场对覆冰特性的影响,这与工程实际情况不相符。在人工气候室内对导线进行带电覆冰,测取了覆冰量和覆冰密度,并通过Q–V法测得了覆冰过程中导线的电晕放电量。为了解释电场对覆冰的影响机制,对交流电晕下水珠的荷电和所受库仑力进行了计算。试验结果表明:试验条件下,覆冰量和覆冰密度随交流场强增加均有先增大后减小的趋势。计算结果表明;电场将对水滴施加电吸力,导致在电晕出现之前或电晕较弱时覆冰量、覆冰密度增加;电晕较强时,空间电荷浓度增加,水滴荷电后所受库仑力起排斥作用,这可能是强电场下导线覆冰量和覆冰密度降低的原因。

细胞电融合技术及最新进展

细胞电融合(cell electrofusion)是一种发展迅速的细胞工程技术,在细胞融合研究领域得到了最广泛的应用。细胞电融合利用细胞在相对电极之间的介电电泳,诱导细胞按特定方向排列,通过电极间产生的较高场强的电脉冲使相互接触的细胞发生电穿孔,进而发生电融合。融合后的细胞得到了不同细胞的遗传物质,具有新的遗传或生物特性。目前,细胞电融合技术对生物医学、农业等相关领域的研究具有非常重要的意义。本文介绍了细胞电融合技术及其最新研究动态,并简单介绍了本实验室在该领域的研究进展。