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.

Control of light scattering by nanoparticles with optically-induced magnetic responses

Conventional approaches to control and shape the scattering pattems of light generated by different nanostructures are mostly based on engineering of their electric response due to the fact that most metallic nanostructures support only electric resonances in the optical frequency range. Recently, fuelled by the fast development in the fields of metamaterials and plasmonics, artificial optically-induced magnetic responses have been demonstrated for various nanostructures. This kind of response can be employed to provide an extra degree of freedom for the efficient control and shaping of the scattering patterns of nanoparticles and nanoantennas. Here we review the recent progress in this research direction of nanoparticle scattering shaping and control through the interference of both electric and optically-induced magnetic responses. We discuss the magnetic resonances supported by various structures in different spectral regimes, and then summarize the original results on the scattering shaping involving both electric and magnetic responses, based on the interference of both spectrally separated （with different resonant wavelengths） and overlapped dipoles （with the same resonant wavelength）, and also other higher-order modes. Finally, we discuss the scattering control utilizing Fano resonances associated with the magnetic responses.

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。

基于平行平板电极的非球面双液体透镜的仿真与实验分析

应用介电泳原理,设计了一种基于平行平板电极的非球面双液体透镜,具有结构简单和易于实现的优点.利用Comsol,Matlab和Zemax软件,建立了相应的非球面双液体透镜光学模型,仿真分析了其在不同电压下的焦距变化及成像特性,并与球面双液体透镜模型进行了比较分析.非球面双液体透镜的变焦范围大于球面的,前者的成像质量亦优于后者.而且,实验制备了该非球面双液体透镜器件,结果表明,在工作电压为0—280 V时,焦距变化为54.2391—34.5855 mm,与仿真结果基本相符,而且该器件的成像分辨率最大可达45.255 lp/mm.

电场作用下含电压稳定剂修复液的扩散及对热氧老化电缆绝缘性能的影响

为了研究含不同类型电压稳定剂的修复液在电场作用下的扩散行为,以及它们对热氧老化电缆绝缘性能的影响。选取安息香、抗氧剂300和UV-P 3种电压稳定剂,配置13组不同含量修复液,进行热氧老化电缆压力注入式修复。对修复前后电缆样本进行红外光谱分析、电树引发和生长实验以及介电性能测试。研究结果表明:修复液注入后,短期内依靠压力和浓度差在绝缘中分层扩散;电场作用使得交联聚乙烯(cross linked polyethylene,XLPE)分子链发生取向、修复液中极性分子受正介电泳力朝电场最强处定向运动,二者促使修复液向绝缘缺陷处加速扩散并聚集,电缆绝缘性能明显提升。不同成分修复液均能提高电缆绝缘的电树引发电压,其中质量分数为1.0%的抗氧剂300修复液对热氧老化电缆的电树抑制效果最好。此外,修复后电缆的直流电导率和介质损耗因数增大,修复液极性对XLPE电缆的绝缘性能和介电性能具有双向作用。

分离富集循环肿瘤细胞的三维介电泳微流控芯片研究

进入人体外周血的肿瘤细胞称为循环肿瘤细胞(CTCs),它是恶性肿瘤转移早期精准检测重要指标之一。基于介电泳原理进行了分离富集CTCs微流控芯片设计及性能研究,利用CTCs和白细胞受到的介电泳力差异及运动轨迹不同,实现CTCs分离富集。根据COMSOL软件仿真细胞运动轨迹,优化芯片结构,确定电极间距和通道高度。湿法刻蚀和激光烧蚀技术制作了芯片实物,以人结肠癌细胞SW480和人白细胞混合液为研究对象,进行了芯片分离富集CTCs实验。在电压为5 Vrms、频率为60 kHz时,三维介电泳微流控芯片对人结肠癌细胞SW480的最大分离通量达到1.2 mL/h,分离效率在90%左右。研究成果对于CTCs分离、分选以及检测等方面具有重要参考价值。

光电镊——一种用途广泛的微纳操作工具

光电镊(OET)是一种基于光致介电泳效应的微尺度光操控技术,可在流体场、光电场、生物力场耦合的复杂环境下对微小目标进行精准操控,在细胞操作、微机械系统等领域有着重要的应用。光电镊技术可以单独使用或与其他技术协同使用,应用十分广泛。迄今为止,基于光电镊的研究主要集中在:微纳米材料的操作、组装和合成;单个细胞/分子的操作、分离和分析;细胞固有特性的分析和获取;细胞的电穿孔、融合和裂解;细胞封装生物材料和生物结构的制备;流体传输的光流体器件的开发。这些工作展示了光电镊技术优越的性能和独特的通用性和灵活性。该文系统地介绍了光电镊技术的现有应用,总结了该技术的应用前景、局限性及发展趋势。