Dielectrophoresis (DEP) is the electrokinetic motion of dielectrically polarized particles in nonuniform electric fields. DEP has found many useful technological applications including separation, levitation and characterization of dielectric particles such as biological cells. In this study, the authors propose a new type of liquid filter, which utilizes dielectrophoretic force (DEP force) to capture fine particles suspended in liquid. The DEP filter consists of an electrode system that is filled up with many dielectric particles. These particles modify the electric field distribution in the electrode system so that strong DEP force is generated on their surfaces. If the DEP force is stronger than drag force exerted by liquid flow in the filter, the suspended particles can be trapped and eliminated from the flowing liquid. The DEP filter can control trapping and releasing process just by changing electrode energizing AC signal and the resultant DEP force. It was experimentally confirmed that the DEP filter could continuously eliminate yeast cells suspended in water. The cell density decreased from 10/sup 6/ cells/mL to 10/sup 1/ cells/mL in about an hour. The electrical conductivity of the medium was a crucial parameter that influenced the liquid temperature by Joule heating and DEP force. Furthermore, the selective separation of viable and nonviable yeast cells was demonstrated by utilizing viability dependency of the DEP force.

Selective separation of cells using dielectrophoresis (DEP) has recently been studied and methods have been proposed. However, these methods are not applicable to large-scale separation because they cannot be performed efficiently. In DEP separation, the DEP force is effective only when it is applied close to the electrodes. Utilizing a DEP filter is a solution for large-scale separation. In this article, the separation efficiency for viable and nonviable cells in a DEP filter was examined. The effects of an applied AC electric field frequency and the gradient of the squared electric field intensity on a DEP velocity for the viable and nonviable animal cells (3-2H3 cell) were discussed. The frequency response of the DEP velocity differed between the viable and the nonviable cells. We deducted an empirical equation that can be used as guiding principle for the DEP separation. The results indicate that the viable and the nonviable cells were separated using the DEP filter, and the best operating conditions such as the applied voltage and the flow rate were discussed.

Recently, studies of selective separation of cells using dielectrophoresis (DEP) have been performed. However, these are not applied to a large scale separation because the separation speed was low. For the problem of the DEP separation, a DEP force is effectively acted only when it is close to the electrode. However, a DEP filter would be one of the answers for a large scale separation.In this paper, we discussed optimization of electrode geometries and arrangement of the DEP filter by using the finite element method (FEM) analysis in order to improve the separation efficiency. A DEP filter electrode using fine wire has a circular cross section, and in this case it became clear that the value of ∂E2/∂y was influenced by the diameter, and the optimum diameter was 0.6 times the electrode gap. Also we discussed for various electrode geometries such as circular, square, diamond, and equilateral triangle electrodes. It became clear that the optimal cross sectional geometry of the DEP filter electrode was square.

Dielectrophoresis (DEP) is the motion of a matter caused by polarization effects in a non-uniform electric field. Recently, studies on DEP are promoted in various medical fields, including separation and characterization of biological cells. It is very important but not easy to measure this motive force, so-called dielectrophoretic force (DEP force). In general, the DEP force generated by the designed electrodes is analyzed by the computer simulation that employs the finite element analysis method. However, it does not always calculate the correct DEP force. Therefore, we propose the method of measuring the DEP force accurately based on the null method. The experiment is conducted with the dielectrophoretic device (DEP device) in which microfabricated electrodes were formed and which contains the polystyrene particles exhibiting the negative DEP in distilled water in a non-uniform electric field. The displacement of the particle reaches a steady state 15 min. after the change of applied voltage v, angle θ or frequency f. The equilibrium state of the particle in a non-uniform electric field can be reached at any place by adjusting both of angles θ and φ, where θ is the “Pitch” angle and φ the “Yaw” angle for the device. The proposed method can measure the incredibly minute DEP force ranging from 25 fN (femto-Newton) at θ=5° to 298 fN at θ=90°, the accuracy of which is determined by the static friction and rolling friction between particles and the inner floor of the DEP device.

A continuous cell separation chip using hydrodynamic dielectrophoresis (DEP) process

This paper presents a high-throughput continuous cell separation chip using hydrodynamic dielectrophoresis (DEP) process. We design the continuous cell separation chip with three electrodes, where the cells in positive DEP affinity are separated from the central streamline. In the experimental study, we use the mixture of viable (live) and nonviable (dead) yeast cells as sample cells to be separated. We obtain the continuous cell separation conditions in the DEP affinity test: the sinusoidal electric fields of 5 MHz, 8V/sub p-p/ have been applied across the electrode array of 20 /spl mu/m gaps immersed in the medium conductivity of 5 /spl mu/S/cm. Using switched AC signal under these conditions, we continuously separate the yeast cells at the mixture flow rates of 0.1/spl sim/1 /spl mu/l/min. The purity of the separated viable and nonviable yeast cells has been measured in the range of 95.9/spl sim/97.3% and 64.5/spl sim/74.3%, respectively.

Dielectrophoresis (DEP) and flow cytometry are powerful technologies and widely applied in microfluidic systems for handling and measuring cells and particles. Here we present a novel microchip with a positive DEP selective filter integrated with two micro flow cytometers for real-time monitoring of cell sorting processes. On the microchip, two flow cytometers are set upstream and downstream of the DEP filter. When a cell pass through the detection windows, the light scattered by the cell is measured by integrated polymer optical elements. The effects of flow rate, applied voltage, conductivity of the sample, and frequency of the electric field on the sorting efficiency of the chip were investigated. Using the chip, viable and non-viable yeast cells were sorted with high efficiency. At 2 MHz, more than 90 % of the viable and less than 10 % of the non-vial cells were captured on the DEP filter. Furthermore, the microstructure is simple to fabricate and can easily be integrated with other microstructures for lab-on-a-chip applications (164).

The complex permittivity of a biological cell reflects its substance and structure and thus seems to reflect its function, activity, abnormality, life/death, age, and life expectancy. Although it may be very difficult to measure the complex permittivity of each cell, the movement or behavior of the cell as affected by its complex permittivity can be observed under the microscope. The dielectrophoretic force (DEP force) generated on a particle in a nonuniform electric field causes movement of the particle in accordance with its complex permittivity or polarizing characteristics. Thus, differences in the substance or structure of biological cells lead to differences in their movement or behavior in a nonuniform electric field. The principle of dielectrophoresis (DEP) and the estimation of the DEP force are described in this chapter. The distinctive features of DEP are applied in the separation of biological cells, e.g., leukocytes from erythrocytes, leukemia cells from normal leukocytes. This cell separation ability is affected by the frequency and amplitude of the applied voltage. To estimate the DEP force generated on a single cell, the terminal velocity of the cell in the medium should be measured withouttaking it out of the DEP device. The procedure to measure the terminal velocity is also described.

Cell focusing and separation is a prerequisite for several biological applications. Among these technologies that can achieve the operation, dielectrophoresis (DEP) has been widely used due to its non-contact, label-free and easy-to-operate advantages. In this paper, we designed a microchip that integrates 3D electrodes and wavy microchannel for cell focusing and separation. The 3D electrodes act as not only the electrodes but also as the microchannel walls. The wavy microchannel enables 3D electrodes to generate electric field gradient required by DEP force in the entire microchannel. Cells can be focused and separated under the synergistic effect of DEP and fluidic forces. We have demonstrated the feasibility of the microchip through numerical simulations and experiments. And we validated our approach by demonstrating focusing and separation of A549 and HeLa cells. According to the electrical differences of cells, in the range of 61–99 kHz, the two types of cells can be focused into three streams under the action of positive and negative DEP force to achieve cell separation. With the increase of the voltage amplitude to 10 V, the width of the cell streams was focused to about 30 μm, which can improve the effect of cell separation, the separation efficiency of A549 and HeLa can reach 91.2% and 95.1%, respectively. The proposed microchip is expected to provide a new pathway for designing an effective cell focusing and separation platform.

Dielectrophoresis (DEP) force will arise when an inhomogeneous AC electric field with sinusoidal wave form is applied to micro electrodes. The DEP is able to distinguish between viable and non-viable biological cells by their movement through a non-uniform electric field. The viable cells can be used for analytic chemistry, cell culture or fusion. The aim of this research is yeast cell culture after distinction of viable and nonviable cells on Au thin-film DEP chip. We fabricated a planar double pole electrode for DEP using Au thin-film and a box cutter. This fabrication method is low cost and simpler than the previous existing methods. We observed cell culture under the terms of DEP (1Vpp-5MHz) after distinction between viable and non-viable yeast cells. The Au thin-film DEP chip could obtain viable cells which were trapped at the micro electrodes. The daughter cell became as big as the mature cells after about 50 minutes of observation. In other experiments, we confirmed whether the Au thin-film DEP chip can trap yeast protoplasts or not. When we applied 4Vpp and over 40kHz, the yeast protoplasts were trapped at the micro electrode. This experimental result is very important for performing fusion of cells. We confirmed usefulness and possibility of Au thin-film DEP chip through these experiments. Keywords-dielectrophoresis; Au thin-film; yeast cell; protoplast; fusion and cell culture

This paper presents a novel design and separation strategy for lateral flow-through separation of cells/particles in microfluidics by dual frequency coupled dielectrophoresis (DEP) forces enabled by vertical interdigitated electrodes embedded in the channel sidewalls. Unlike field-flow-fractionation-DEP separations in microfluidics, which utilize planar electrodes on the microchannel floor to generate a DEP force to balance the gravitational force and separate objects at different height locations, lateral separation is enabled by sidewall interdigitated electrodes that are used to generate non-uniform electric fields and balanced DEP forces along the width of the microchannel. In the current design, two separate AC electric fields are applied to two sets of independent interdigitated electrode arrays fabricated in the sidewalls of the microchannel to generate differential DEP forces that act on the cells/particles flowing through. Individual particles (cells or beads) will experience DEP forces differently due to the difference in their dielectric properties. The balance of the differential DEP forces from the electrode arrays will position dissimilar particles at distinct equilibrium planes across the width of the channel. When coupled with fluid flow, this results in lateral separation along the width of the microchannel and the separated particles can thus be automatically directed into branched channel outlets leading to different reservoirs for downstream processing. In this paper, we present the design and analysis of lateral separation enabled by dual frequency coupled DEP, and cell/bead and cell/cell separations are demonstrated with this lateral separation strategy. With vertical interdigitated electrodes on the sidewall, the height of the microchannel can be increased without losing the electric field strength in contrast to other multiple frequency DEP devices with planar electrodes. As a result, populations of cells can be separated simultaneously instead of one by one to enable high-throughput sorting microfluidic devices.

This study reports a new biochip capable of cell separation and nucleus collection utilizing dielectrophoresis (DEP) forces in a microfluidic system comprising of micropumps and microvalves, operating in an automatic format. DEP forces operated at a low voltage (15 Vp-p) and at a specific frequency (16 MHz) can be used to separate cells in a continuous flow, which can be subsequently collected. In order to transport the cell samples continuously, a serpentine-shape (S-shape) pneumatic micropump device was constructed onto the chip device to drive the samples flow through the microchannel, which was activated by the pressurized air injection. The mixed cell samples were first injected into an inlet reservoir and driven through the DEP electrodes to separate specific samples. Finally, separated cell samples were collected individually in two outlet reservoirs controlled by microvalves. With the same operation principle, the nucleus of the specific cells can be collected after the cell lysis procedure. The pumping rate of the micropump was measured to be 39.8 microl/min at a pressure of 25 psi and a driving frequency of 28 Hz. For the cell separation process, the initial flow rate was 3 microl/min provided by the micropump. A throughput of 240 cells/min can be obtained by using the developed device. The DEP electrode array, microchannels, micropumps and microvalves are integrated on a microfluidic chip using micro-electro-mechanical-systems (MEMS) technology to perform several crucial procedures including cell transportation, separation and collection. The dimensions of the integrated chip device were measured to be 6x7 cm. By integrating an S-shape pump and pneumatic microvalves, different cells are automatically transported in the microchannel, separated by the DEP forces, and finally sorted to specific chambers. Experimental data show that viable and non-viable cells (human lung cancer cell, A549-luc-C8) can be successfully separated and collected using the developed microfluidic platform. The separation accuracy, depending on the DEP operating mode used, of the viable and non-viable cells are measured to be 84 and 81%, respectively. In addition, after cell lysis, the nucleus can be also collected using a similar scheme. The developed automatic microfluidic platform is useful for extracting nuclear proteins from living cells. The extracted nuclear proteins are ready for nuclear binding assays or the study of nuclear proteins.

Both dielectrophoresis (DEP) and flow cytometry are widely applied in microfluidic systems for the handling and measurements of cells and particles. Here, we present a novel integrated microchip, combining a DEP selective filter with flow cytometers for real-time monitoring of the cell sorting processes. The DEP filter was integrated inside a microfluidic channel to sort cells by positive DEP. The cells were hydrodynamically focused to the center of the channel by using a sheath flow from either side. Two flow cytometer (FC) detection windows were set upstream and downstream, respectively, from the DEP filter to measure the forward scattered light of passing cells. Comparing the cell counting rates measured on two different FCs, the collection efficiency of the DEP filter could be determined. This microchip was used to quantitatively monitor the sorting of viable from nonviable yeast cells.

Dielectrophoresis (DEP) force is a widely studied topic because it has high utility in various research areas. Understanding DEP force is significant from the point of view of its efficient usage. Here, we confirmed the directions and magnitudes of DEP forces for metallic and non-metallic particle manipulations as well as force measurements via a quartz tuning fork atomic force microscopy (QTF-AFM) system. The 100 nm non-metallic silica particles having negative DEP force move toward the minimum point of the square of the electric field while the 60 nm metallic Au particles have positive DEP force. We also measured the magnitude of the DEP force in a liquid environment with electrodes. The experimentally measured DEP force magnitude was about 1 nN, which was similar to the simulation results, and the tendency of the measured force was consistent with that of the simulated case. This shows the possibility of using a QTF-AFM system as the fine force sensor in a liquid environment.

Dielectrophoresis (DEP) is the motion of colloidal particles in an inhomogeneous electric field. Accurate determination of dielectrophoresis (DEP) force is important for lab-on-a-chip applications. However current DEP force spectroscopy methods are not suitable for accurately measuring the DEP force for sub-micron particles. A new and facile method is developed to measure the DEP force as a function of the frequency of the electric field for nanoparticles by an ensemble analysis approach. Using the principle of Boltzmann distribution of the concentration of non-interacting particles in a DEP potential field, the new method determines the DEP potential field from the measured time-averaged concentration distribution of fluorescently labeled nanoparticle in the DEP field by confocal fluorescence microscopy. Frequency dependent DEP force is determined by the negative gradient of the DEP potential created by the electric field across gold-film electrodes in a microfluidic setting. This approach is capable of measuring forces at the level of one femto Newton for particles with diameters in the range of 63 nm to 410 nm.