Diamagnetic capture mode magnetophoretic microseparator for blood cells

This paper presents the characterization of a continuous diamagnetic capture (DMC) mode magnetophoretic microseparator for separating red and white blood cells from diluted whole blood based on their native magnetic properties. The DMC microseparator separated the blood cells using a high-gradient magnetic separation (HGMS) method without the use of additives such as magnetic beads. The microseparator was fabricated using microfabrication technology, enabling the integration of microscale magnetic flux concentrators in an aqueous microenvironment. Experimental results show that the DMC microseparator can continuously separate out 89.7% of red blood cells (RBCs) from diluted whole blood within 5 min using an external magnetic flux of 0.2 T from a permanent magnet. Monitoring white blood cells (WBCs) probed with a fluorescence dye show that 72.7% of WBCs were separated out within 10 min in the DMC microseparator using a 0.2 T external applied magnetic flux. Consequently, the DMC microseparator may facilitate the separation of WBCs from whole blood in applications such as a genetic sample preparation and blood borne disease detection. [1574].     

Bioparticle separation and manipulation using dielectrophoresis

Manipulation and separation of micro-sized particles, particularly biological particles, using the dielectrophoretic (DEP) force is an emerging technique in MEMS technology. This paper presents a DEP-based microsystem for the selective manipulation and separation of bioparticles using dielectrophoretic effects. The microfabricated DEP device consists of a sandwich structure, in which a microchannel with electrode array lining on its bottom is sandwiched between the substrate and the glass lid. Dielectrophoretic behavior of polystyrene particles with diameter of 4.3 μm was studied. Both positive DEP and negative DEP were observed. Particles under positive DEP were attracted to the edges of the electrodes, while those under negative DEP were repelled away from the electrodes and levitated at certain height above the electrodes (within a proper range of frequencies of the electric field). Levitation height of the particles was measured. It was demonstrated that the levitation height of a specific particle strongly depends on the combined contributions of a number of parameters, such as the frequency of the electric field, dielectric properties of the particles and the surrounding medium. Different particles can be separated and manipulated on the basis of their difference in these parameters.     

基于微环形阵列电极的细胞分离富集芯片的设计与实验研究

根据介电泳操作原理,设计了微环形阵列电极结构,建立了细胞分离富集芯片模型,采用COMSOL软件分析微环形阵列电极的电场分布和介电泳力方向并确定了最大和最小电场强度的位置,利用ITO玻璃和PDMS制备了细胞分离富集芯片.通过酵母菌细胞的介电泳富集实验和酵母菌细胞与聚苯乙烯小球的分离富集实验,明确了酵母菌细胞的临界频率,实现了酵母菌细胞和聚苯乙烯小球的分离富集.结果显示,在溶液电导率为60μs/cm,交流信号电压为8Vp-p时,酵母菌细胞在1kHz~45kHz频率范围内做负介电泳运动并富集在环形内部,45kHz为酵母菌细胞的临界频率,在45kHz~10MHz频率范围内做正介电泳运动并富集在环形边缘;1.5MHz时聚苯乙烯小球做负介电泳运动并富集在环形内部,富集倍数达到11.66.     

Improved concentration and separation of particles in a 3D dielectrophoretic chip integrating focusing, aligning and trapping

This article presents a dielectrophoresis (DEP)-based microfluidic device with the three-dimensional (3D) microelectrode configuration for concentrating and separating particles in a continuous throughflow. The 3D electrode structure, where microelectrode array are patterned on both the top and bottom surfaces of the microchannel, is composed of three units: focusing, aligning and trapping. As particles flowing through the microfluidic channel, they are firstly focused and aligned by the funnel-shaped and parallel electrode array, respectively, before being captured at the trapping unit due to negative DEP force. For a mixture of two particle populations of different sizes or dielectric properties, with a careful selection of suspending medium and applied field, the population exhibits stronger negative DEP manipulated by the microelectrode array and, therefore, separated from the other population which is easily carried away toward the outlet due to hydrodynamic force. The functionality of the proposed microdevice was verified by concentrating different-sized polystyrene (PS) microparticles and yeast cells dynamically flowing in the microchannel. Moreover, separation based on size and dielectric properties was achieved by sorting PS microparticles, and isolating 5 μm PS particles from yeast cells, respectively. The performance of the proposed micro-concentrator and separator was also studied, including the threshold voltage at which particles begin to be trapped, variation of cell-trapping efficiency with respect to the applied voltage and flow rate, and the efficiency of separation experiments. The proposed microdevice has various advantages, including multi-functionality, improved manipulation efficiency and throughput, easy fabrication and operation, etc., which shows a great potential for biological, chemical and medical applications.     

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]      

A microfabricated module for isolating cervical carcinoma cells from peripheral blood utilizing dielectrophoresis in stepping electric fields

The ability to isolate rare cells, such as circulating tumor cells (CTC), circulating fetal cells, and stem cells, is important for medical diagnostics and characterization. The present study develops a microfabricated module that can effectively isolate cervical carcinoma cells (HeLa) from a peripheral blood sample. Circular microelectrodes that generate a stepping electric field by switching the electric field between adjacent electrode pairs by relays are designed herein. Positive dielectrophoretic cells are guided by the movement of the high-electric-field region. The magnitude of the dielectrophoresis (DEP) force acting on HeLa cells is about sevenfold that on red blood cells (RBCs) under a given electric field distribution in a sucrose medium, making it possible to separate HeLa cells from normal blood cells. Both HeLa cells and RBCs are pushed to the outermost electrodes when an outward stepping electric field (16?V peak-to-peak; 1?MHz) is applied. When an inward stepping electric field (10?V peak-to-peak; 1?MHz) is applied, the movement of HeLa cells toward the center electrodes is faster than that of RBCs. As a result, HeLa cells are concentrated onto the central microelectrode and isolated from the blood sample. Experimental results demonstrate the feasibility of isolating HeLa cells from blood samples.     

Nanomanipulation of single influenza virus using dielectrophoretic concentration and optical tweezers for single virus infection to a specific cell on a microfluidic chip

A major problem when analyzing bionanoparticles such as influenza viruses (approximately 100 nm in size) is the low sample concentrations. We developed a method for manipulating a single virus that employs optical tweezers in conjunction with dielectrophoretic (DEP) concentration of viruses on a microfluidic chip. A polydimethylsiloxane microfluidic chip can be used to stably manipulate a virus. The chip has separate sample and analysis chambers to enable quantitative analysis of the virus functions before and after it has infected a target cell. The DEP force in the sample chamber concentrates the virus and prevents it from adhering to the glass substrate. The concentrated virus is transported to the sample selection section where it is trapped by optical tweezers. The trapped virus is transported to the analysis chamber and it is brought into contact with the target cell to infect it. This paper describes the DEP virus concentration for single virus infection of a specific cell. We concentrated the influenza virus using the DEP force, transported a single virus, and made it contact a specific H292 cell.     

A Programmable Biochip for the Applications of Trapping and Adaptive Multisorting Using Dielectrophoresis Array

The adaptive biochip integrating dielectrophoresis (DEP) traps and a programmable multisorting DEP array for the multisorting applications of biomolecules such as proteins and DNA is proposed and demonstrated in this paper. In this research, movable beads are used as the mobile probes to capture the target protein molecules. These beads are chemically modified and immobilized with p50 proteins in our demonstration. An array of micropyramid DEP traps with a good levitation control on the height of the beads is located at the upstream to enhance the hybridization function of the mobile probes. The sample solution mixed with Cy3-I-kappa-B-alpha complex is used in the demonstration. A programmable multisorting DEP array that is located at the downstream sorts out the hybridized beads, which are fluorescently labeled based on the fluorescent detection signals. The magnitude and direction of the DEP force that is applied to the beads with/without labeling fluorescence in the multisorting DEP array are controlled via the distribution of time-variant nonuniform electric fields. The voltage on the individual electrode of the multisorting DEP array is preprogrammed and controlled by a LabVIEW controller with fluorescence detection feedback signals. In contrast to the research of Manaresi et al. [IEEE J. Solid-State Circuits, vol. 38, no. 12, p. 2297, 2003], which was proposed for trapping and sorting beads and cells via Dent traps, to our knowledge, the design of this biochip with the hybridization enhancement via micropyramid DEP traps and the adaptive multisorting DEP array for the mobile probes has never been proposed and implemented to date.     

Computational and performance analysis of a continuous magnetophoretic bioseparation chip with alternating magnetic fields

This paper presents the modeling and optimization of a magnetophoretic bioseparation chip for isolating cells, such as circulating tumor cells from the peripheral blood. The chip consists of a continuous-flow microfluidic platform that contains locally engineered magnetic field gradients. The high-gradient magnetic field produced by the magnets is spatially non-uniform and gives rise to an attractive force on magnetic particles flowing through a fluidic channel. Simulations of the particle–fluid transport and the magnetic force are performed to predict the trajectories and capture lengths of the particles within the fluidic channel. The computational model takes into account key forces, such as the magnetic and fluidic forces and their effect on design parameters for an effective separation. The results show that the microfluidic device has the capability of separating various cells from their native environment. An experimental study is also conducted to verify and validate the simulation results. Finally, to improve the performance of the separation device, a parametric study is performed to investigate the effects of the magnetic bead size, cell size, number of beads per cell, and flow rate on the cell separation performance.     

Development of a μ-concentrator Using Dielectrophoretic Forces

We present the simulation, development and experimental validation of a μ-concentrator based on dielectrophoresis, DEP.In a first step dielectrophoretic force fields of various electrodes are computed and compared. The simulation results for various electrode dimensions may serve as a general design rule for DEP devices. Favorable electrode designs were realized in gold on glass substrates. The performance of the DEP chips is validated by concentration of E.-Coli bacteria, a separation efficiency of 99.93% was achieved. Furthermore, we outline how the combination of forced convection and DEP allows for bacteria separation at increased flow rates.     

Continuous size-based focusing and bifurcating microparticle streams using a negative dielectrophoretic system

Dielectrophoresis (DEP) is an electrokinetic phenomenon which is used for manipulating micro- and nanoparticles in micron-sized devices with high sensitivity. In recent years, electrode-based DEP by patterning narrow oblique electrodes in microchannels has been used for particle manipulation. In this theoretic study, a microchannel with triangular electrodes is presented and a detailed comparison with oblique electrodes is made. For each shape, the behavior of particles is compared for three different configurations of applied voltages. Electric field, resultant DEP force, and particle trajectories for configurations are computed by means of Rayan native code. The separation efficiency of the two systems is assessed and compared afterward. The results demonstrate higher lateral DEP force, responsible for particle separation, distributed wider across the channel width for triangular shape electrodes in comparison with the oblique ones. The proposed electrode shape also shows the ability of particle separation by attracting negative DEP particles to or propelling them from the flow centerline, according to the configuration of applied voltages. A major deficiency of the oblique electrodes, which is the streamwise variation of the lateral DEP force direction near the electrodes, is also eliminated in the proposed electrode shape. In addition, with a proper voltages configuration, the triangular electrodes require lower voltages for particle focusing in comparison with the oblique ones.     

Dielectrophoretic separation of carbon nanotubes and polystyrene microparticles

The separation of multi-walled carbon nanotubes (MWCNTs) and polystyrene microparticles using a dielectrophoresis (DEP) system is presented. The DEP system consists of arrays of parallel microelectrodes patterned on a glass substrate. The performance of the system is evaluated by means of numerical simulations. The MWCNTs demonstrate a positive DEP behaviour and can be trapped at the regions of high electric field. However, the polystyrene microparticles demonstrate a negative DEP behaviour at a certain range of frequencies and migrate to the regions of low electric field. Experiments are performed on the microparticles at the frequencies between 100 Hz and 1 MHz to estimate their crossover frequency and select the range of separation frequencies. Further, experiments are conducted at the obtained range of separation frequencies to separate the MWCNTs and polystyrene microparticles.     

On-chip separation of Lactobacillus bacteria from yeasts using dielectrophoresis

Dielectrophoresis, the induced motion of dielectric particles in non-uniform electric fields, enables the separation of suspended bio-particles based on their dimensions or dielectric properties. This work presents a microfluidic system, which utilises a combination of dielectrophoretic (DEP) and hydrodynamic drag forces to separate Lactobacillus bacteria from a background of yeasts. The performance of the system is demonstrated at two operating frequencies of 10?MHz and 100?kHz. At 10?MHz, we are able to trap the yeasts and bacteria at different locations of the microelectrodes as they experience different magnitudes of DEP force. Alternatively, at 100?kHz we are able to trap the bacteria along the microelectrodes, while repelling the yeasts from the microelectrodes and washing them away by the drag force. These separation mechanisms might be applicable to automated lab-on-a-chip systems for the rapid and label-free separation of target bio-particles.     

基于石英和载玻片的微电极制备工艺研究

研究以石英片和载玻片为基底的微电极制备工艺,以较常见的叉指型电极为例,基于光刻工艺中各工艺参数要求,重点研究曝光和显影时间对微电极的影响。制得的2种不同基底的电极,采用对比度、精度等关键参数进行分析,最终确定选用载玻片作为芯片基底并获得其最佳工艺参数;制作带电极的PDMS—玻璃微流控芯片,通过实验,成功观察到酵母菌细胞的正、负介电泳现象。     

Droplet creation using liquid dielectrophoresis

Dielectrophoresis (DEP) is defined as polarizable particles moving into regions of higher electric field intensity. In liquid DEP (LDEP), a dielectric liquid tends to flow toward regions of high electric field intensity under a non-uniform electric field. This work presents a theoretical model of LDEP based on parallel electrodes. The LDEP force is derived using the lump parameter electromechanical method. The relationship between the minimum actuation voltage and the electrode width is investigated experimentally and theoretically. We also propose a method for creating a 20 nl droplet of deionized water using LDEP. The creation of a water droplet containing 15 μm polystyrene beads is placed at the desired location from a continuous flow driven by LDEP using the developed method.     

Simultaneous electrokinetic flow and dielectrophoretic trapping using perpendicular static and dynamic electric fields

Microfluidics is a rapidly growing field that offers great potential for many biological and analytical applications. There are important advantages that miniaturization has to offer, such as portability, shorter response times, higher resolution and sensitivity. There is growing interest on the development of microscale techniques. Among these, electrokinetic phenomena have gained significant importance due to their flexibility for handling bioparticles. Dielectrophoresis (DEP), the manipulation of particles in non-uniform electric fields due to polarization effects, has become one of leading electrokinetic techniques. DEP has been successfully employed to manipulate proteins, DNA and a wide array of cells, form bacteria to cancer. Contactless DEP (cDEP) is a novel dielectrophoretic mode with attractive characteristics. In cDEP, non-uniform electric fields are created using insulating structures and external electrodes that are separated from the sample by a thin insulating barrier. This prevents bioparticle damage and makes cDEP a technique of choice for many biomedical applications. In this study, a combination of cDEP generated with AC potentials and electrokinetic liquid pumping generated with DC potentials is employed to achieve highly controlled particle trapping and manipulation. This allows for lower applied potentials than those used in traditional insulator-based DEP and requires a simpler sytem that does not employ an external pump. This is the first demonstration of electrokinetic (EK) pumping in which the driving electrodes are not in direct contact with the sample fluid. Multiphysics simulations were used to aid with the design of the system and predict the regions of particle trapping. Results show the advantages of combining AC-cDEP with DC EK liquid pumping for dynamic microparticle trapping, release and enrichment.     

Pattern recognition of nucleated cells from the peripheral blood

A data set consisting of 2259 nucleated cells from the peripheral blood, including immature cells, was systematically investigated using image processing and pattern recognition techniques. A total of 94.2% of all cells could be correctly classified into one of 9 possible main classes. Several subsets were also investigated. In particular, the cell types in the neutrophilic maturation sequence were extensively explored.     

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.     

Selective position of individual cells without lysis on a circular window array using dielectrophoresis in a microfluidic device

We trapped individual cells between two circular windows using negative dielectrophoretic (DEP) force and then sequentially trapped them inside circular windows by positive DEP force without electrical lysis in a microfluidic device. Three parameters, (1) the transmembrane potential that determines the lysis of a cell, (2) individual cell size that affects the trapped position accuracy of the cell, and (3) the Clausius–Mossotti (CM) factor that decides the trapped efficiency of the cell, were characterized experimentally and numerically in this sequential cell trapping technique. In this characterization, we confirmed that the swap rate of applied voltage frequency, size similarity between the cell and circular window, and instantaneous change rate of Re(f _CM) as a function of frequency were important factors in determining the selective position of individual cells without lysis. Our results provide useful suggestions for designing the structure of microfluidic DEP devices and optimizing variables required to manipulate individual cell trapping using both negative and positive DEP forces.     

Study on the assembly and separation of biological cell by optically induced dielectrophoretic technology

Optically induced dielectrophoretic (ODEP) chip is to combine their own advantages of optical tweezers and electrodynamics manipulation technologies, which can trap single particles in high resolution as well as enrich much of micro-/nanoparticles in high throughput. The paper analyzed the structure of optoelectronic tweezers (OET) chip, moreover, the frequency response of multi-membrane eukaryotic cells about 10³–10⁹ Hz. The Clausius–Mositti (CM) frequency factor in terms of cell membrane, cell cytoplasm, nuclear envelope thickness changes, and volume ratio was illustrated. In the end, the paper presented 3D numeric model of cells in OET chip. The dielectrophoresis force acting on the dipole of 11.8-μm cells subjected to a non-uniform electric field under 60-μm Gaussian-distributed beam spot could be simulated in the enrichment process. The separation of cells that were two different types of CM values was calculated. Furthermore, it was proved to be feasible to achieve the efficient separation of cells using ODEP technology in the biological numerical model. Comparing with the literature of experiment, the results in cell dielectric spectroscopy and numeric model findings were in general agreement. The simplified structure and numeric model of nucleated cell provide a theoretical basis for research of biosensor and complex life.