Dielectrophoretic Separation Research Articles

Characterization of Microelectrode Array of Dielectrophoretic Microfluidic Device

This paper presents the characterization of angled microelectrode array as dielectrophoretic microfluidic device for the continuous flow-through separation of particles. The operation of the device is demonstrated using samples of colloidal latex beads of 1 μm and 2 μm in diameter sizes, achieving 100% particle deflection with operating voltage as low as 10V and frequency as minimum as 1 MHz. This characterization is essential for dielectrophoretic separation to get the specific suggestion for each type of particle behavior via its own deflection throughout the arrays of the angled microelectrode. The paper also exhibits and discusses the detail of the theoretical background of the separation method; the structure of the device and also the result obtained that is achievable by choice of voltage and frequency.

Numerical simulation of dielectrophoretic separation of live/dead cells using a three-dimensional nonuniform AC electric field in micro-fabricated devices

The analysis of cell separation has many important biological and medical applications. Dielectrophoresis (DEP) is one of the most effective and widely used techniques for separating and identifying biological species. In the present study, a DEP flow channel, a device that exploits the differences in the dielectric properties of cells in cell separation, was numerically simulated and its cell-separation performance examined. The samples of cells used in the simulation were modeled as human leukocyte (B cell) live and dead cells. The cell-separation analysis was carried out for a flow channel equipped with a planar electrode on the channel's top face and a pair of interdigitated counter electrodes on the bottom. This yielded a three-dimensional (3D) nonuniform AC electric field in the entire space of the flow channel. To investigate the optimal separation conditions for mixtures of live and dead cells, the strength of the applied electric field was varied. With appropriately selected conditions, the device was predicted to be very effective at separating dead cells from live cells. The major advantage of the proposed method is that a large volume of sample can be processed rapidly because of a large spacing of the channel height.

Predicting and eliminating Joule heating constraints in large dielectrophoretic IDE separators

Dielectrophoresis (DEP), a measure to manipulate motion trajectories of suspended particles, has a high potential for solving difficult particle–liquid separation problems. Applications of DEP so far have been limited to micro-channels and lab-on-a-chip devices. However, for designing DEP separators with sufficiently high throughput to reach preparative scale, an understanding of the interplay of channel geometry and electrode concept with respect to induced particle velocity is required. The objective of tailored design is a control of particle motion trajectories predominantly by DEP while avoiding electrothermal interference. It is Joule heating, which gives rise to temperature gradients in the liquid phase and, thus, induces thermal convection. In this work we demonstrate that a solution of this Joule heating problem in large scale DEP systems is a tailored ratio of electrode diameter, electrode distance, and channel height. Based on model calculations we predicted the influence of both DEP force and drag force through thermal convection on particle trajectories for a case study, a channel with rectangular cross section and an array of cylindrical interdigitated electrodes (IDE) at the bottom. These theoretical results were verified experimentally by measured velocities of polyelectrolytic resin microparticles located at the subsurface of demineralized water. This allowed for a qualitative sensitivity analysis of the impact of voltage input, particle size and medium properties on the critical design parameter. From this, design criteria were deduced for the IDE–DEP system that allow for minimizing the influence of Joule heating. The findings demonstrate that, even if high voltages are applied, Joule heating problems can be effectively suppressed in DEP system scale-up.

CFD design of a microfluidic device for continuous dielectrophoretic separation of charged gold nanoparticles

Separation of biological as well as, non-biological nanoparticles have primarily been done by trapping, which has to be carried out in a batch mode. Continuous separation would not only increase the throughput but would be less cumbersome. In the present work, therefore, a new design of a microfluidic device for continuous separation of charged metal nanoparticles (gold) by dielectrophoresis (DEP) has been proposed. The effect of the electrical double layer (EDL) on the DEP separation has also been considered in this study. The effective complex permittivity of the neutral particle is estimated using the multishell model, which takes into account the complex permittivities of both the charged particle and the EDL. Microelectrodes of unequal size are embedded on the vertical side walls to generate a non-uniform electric field along the width of the microchannel. Size separation of nanoparticles takes place based on the DEP force experienced by them. Computational fluid dynamic simulations have been carried out to optimize the design and process parameters for continuous separation, by negative DEP, of charged gold nanoparticles of size 30 nm and 60 nm. Sensitivity analysis has also been carried out to study the effect of different parameters on the separation efficiency for the proposed design.

Continuous dielectrophoretic particle separation using a microfluidic device with 3D electrodes and vaulted obstacles.

This paper reports a microfluidic separation device combining 3D electrodes and vaulted obstacles to continuously separate particles experiencing strong positive dielectrophoresis (DEP) from particles experiencing weak positive DEP, or from particles experiencing negative DEP. The separation is achieved by first focusing the particle mixture into a narrow stream by a hydrodynamic focusing flow, and then deviating them into different outlets by AC DEP. The vaulted obstacles facilitate the separation by both increasing the non-uniformity of the electric field, and influencing the particles to move in regions strongly affected by DEP. The 3D electrodes give rise to a spatially non-uniform electric field and extend DEP effect to the channel height. Numerical simulations are performed to investigate the effects of the obstacles on electric field distribution and particle trajectories so as to optimize the obstacle height and compare with the experimental results. The performance of the device is assessed by separating 25 μm gold-coated particles from 10μm particles in different flow rates by positive DEP and negative DEP, and also separating 25 μm gold-coated particles from yeast cells using only positive DEP. The experimental observation shows a reasonable agreement with numerical simulation results.

Differential dielectric responses of chondrocyte and Jurkat cells in electromanipulation buffers.

Electromanipulation of cells as a label-free cell manipulation and characterization tool has gained particular interest recently. However, the applicability of electromanipulation, particularly dielectrophoresis (DEP), to biological cells is limited to cells suspended in buffers containing lower amounts of salts relative to the physiological buffers. One might question the use of low conductivity buffers (LCBs) for DEP separation, as cells are stressed in buffers lacking physiological levels of salt. In LCB, cells leak ions and undergo volume regulation. Therefore, cells exhibit time-dependent DEP response in LCB. In this work, cellular changes in LCB are assessed by dielectric spectroscopy, cell viability assay, and gene expression of chondrocytes and Jurkats. Results indicate leakage of ions from cells, increases in cytoplasmic conductivity, membrane capacitance, and conductance. Separability factor, which defines optimum conditions for DEP cell separation, for the two cell types is calculated using the cellular dielectric data. Optimum DEP separation conditions change as cellular dielectric properties evolve in LCB. Genetic analyses indicate no changes in expression of ionic channel proteins for chondrocytes suspended in LCB. Retaining cellular viability might be important during dielectrophoretic separation, especially when cells are to be biologically tested at a downstream microfluidic component.

Device for dielectrophoretic separation and collection of nanoparticles and DNA under high conductance conditions.

Most dielectrophoretic (DEP) separations of cells, nanoparticles, and other entities are carried out on microelectrode arrays or in microfluidic device formats. Less work has been directed at designing pipette-type formats that would allow dipping into and recovering specific analytes from samples in microtiter plate formats. In order to address this important area, we have fabricated micropipette tip devices containing a 2% agarose gel plug, a buffer chamber, and platinum electrode as the DEP collection device, to be used in combination with separate sample wells that contain a circular gold electrode. We demonstrated that 200 nm fluorescent nanoparticles could be isolated into DEP high-field regions and separated from 10 μm fluorescent microbeads in high conductance buffer (1× PBS) by applying an alternating current at 10 kHz with a peak-to-peak voltage (Vpp) of 160 Vpp. The collected nanoparticles were then transferred to a new buffer solution. We also demonstrated the DEP isolation and separation of genomic DNA (>50 kbps) from the 10 μm microbeads in high conductance buffer (1× PBS) with transfer of collected DNA to another solution.

Enhanced sub-micron colloidal particle separation with interdigitated microelectrode arrays using mixed AC/DC dielectrophoretic scheme.

Dielectrophoretic separation of particles finds a variety of applications in the capture of species such as cells, viruses, proteins, DNA from biological systems, as well as other organic and inorganic contaminants from water. The ability to capture particles is constrained by poor volumetric scaling of separation force with respect to particle diameter, as well as the weak penetration of electric fields in the media. In order to improve the separation of sub-micron colloids, we present a scheme based on multiple interdigitated electrode arrays under mixed AC/DC bias. The use of high frequency longitudinal AC bias breaks the shielding effects through electroosmotic micromixing to enhance electric fields through the electrolyte, while a transverse DC bias between the electrode arrays enables penetration of the separation force to capture particles from the bulk of the microchannel. We determine the favorable biasing conditions for field enhancement with the help of analytical models, and experimentally demonstrate the improved capture from sub-micron colloidal suspensions with the mixed AC/DC electrostatic excitation scheme over conventional AC-DEP methods.

Dielectrophoretic sample preparation for environmental monitoring of microorganisms: Soil particle removal.

Detection of pathogens from environmental samples is often hampered by sensors interacting with environmental particles such as soot, pollen, or environmental dust such as soil or clay. These particles may be of similar size to the target bacterium, preventing removal by filtration, but may non-specifically bind to sensor surfaces, fouling them and causing artefactual results. In this paper, we report the selective manipulation of soil particles using an AC electrokinetic microfluidic system. Four heterogeneous soil samples (smectic clay, kaolinitic clay, peaty loam, and sandy loam) were characterised using dielectrophoresis to identify the electrical difference to a target organism. A flow-cell device was then constructed to evaluate dielectrophoretic separation of bacteria and clay in a continous flow through mode. The average separation efficiency of the system across all soil types was found to be 68.7% with a maximal separation efficiency for kaolinitic clay at 87.6%. This represents the first attempt to separate soil particles from bacteria using dielectrophoresis and indicate that the technique shows significant promise; with appropriate system optimisation, we believe that this preliminary study represents an opportunity to develop a simple yet highly effective sample processing system.

Dielectrophoretic separation of bioparticles in microdevices: A review

In recent years, dielectrophoretic force has been used to manipulate colloids, inert particles, and biological microparticles, such as red blood cells, white blood cells, platelets, cancer cells, bacteria, yeast, microorganisms, proteins, DNA, etc. This specific electrokinetic technique has been used for trapping, sorting, focusing, filtration, patterning, assembly, and separating biological entities/particles suspended in a buffer medium. Dielectrophoretic forces acting on particles depend on various parameters, for example, charge of the particle, geometry of the device, dielectric constant of the medium and particle, and physiology of the particle. Therefore, to design an effective micro-/nanofluidic separation platform, it is necessary to understand the role of the aforementioned parameters on particle motion. In this paper, we review studies particularly related to dielectrophoretic separation in microfluidic devices. Both experimental and theoretical works by several researchers are highlighted in this article covering AC and DC DEP. In addition, AC/DC DEP, which uses a combination of low frequency AC and DC voltage to manipulate bioparticles, has been discussed briefly. Contactless DEP, a variation of DC DEP in which electrodes do not come in contact with particles, has also been reviewed. Moreover, dielectrophoretic force-based field flow fractionations are featured to demonstrate the bioparticle separation in microfluidic device. In numerical front, a comprehensive review is provided starting from the most simplified effective moment Stokes-drag (EMSD) method to the most advanced interface resolved method. Unlike EMSD method, recently developed advanced numerical methods consider the size and shape of the particle in the electric and flow field calculations, and these methods provide much more accurate results than the EMSD method for microparticles.

Cell Separation

Cell Separation

Improvement of DEP Cell Sorter by Design of Flow Channel for Higher Field Gradient

SummaryIn this study, high separation ratio microfluidic cell sorting by a dielectrophoretic (DEP) force is presented. The recent development of iPS cell technology has raised the possibility of regenerative therapy. Technologies of genetic cell processing require purification of specific target cells by a cell sorter. The most widely used system for cell separation is flow cytometry (FCM), which has been developed for research purposes. Despite the excellent separation ratio it achieves, it has a rather high cost per operation. For clinical use, devices contacting biological specimens must be disposable to prevent cross‐infection. A low cost microfluidic cell sorter, using the DEP force, can be fabricated by photolithography. However, the sorting rate of existing DEP cell sorters is far lower than that of FCM because of limitations of the applicable voltage in an aqueous fluid. To circumvent the problem and raise the DEP force, the implementation of field gradient dependence was investigated. The flow channel was designed to produce a high gradient at the separation point and to enhance the DEP force. Numerical calculations by the finite element method indicate that the electric field distribution has a peak intensity at the entrance to the separation channel. DEP separation of latex beads 2 m in diameter at a flow speed of 3.0 mm/s, six times that of our previous system, was demonstrated.

Purification of titanate nanotubes using a mesh-stacked dielectrophoretic separator equipped with carbon nanotube electrodes

A mesh-stacked dielectrophoretic (MS-DEP) separator whose electrodes were covered with multi-walled carbon nanotubes (MWCNTs) was built to purify titanate nanotubes (TNTs) synthesized by hydrothermal conversion from anatase TiO2 powders. MWCNTs were synthesized directly on the surface of stainless mesh electrodes. It was experimentally observed that this MS-DEP separator could be useful to purify TNTs. It was found that relatively low frequency for AC voltage applied on the MS-DEP separator was preferable when it was required to collect TNTs possessing a large energy bandgap. In addition, a model calculation was carried out to qualitatively discuss the effect of MWCNT to enhance the electric field strength at MWCNTs, which could generate the strong DEP force on small particles.

1E45 3D不平等電界を用いた誘電泳動による細胞分離(OS2-4:細胞・分子のバイオメカニクス(4))

1E45 3D不平等電界を用いた誘電泳動による細胞分離(OS2-4:細胞・分子のバイオメカニクス(4))

Helical Dielectrophoretic Particle Separator Fabricated by Conformal Spindle Printing

This paper reports the fabrication and testing of a helical cell separator that uses insulator-based dielectrophoresis as the driving force of its separation. The helical channel shape’s main advantage is its constant curvature radius which generates a constant electric field gradient. The presented separator was fabricated by extruding a sacrificial ink on rotating spindles using a computer-controlled robot. After being assembled, connected to the reservoir and encapsulated in epoxy resin, the ink was removed to create a helical microchannel. The resulting device was tested by circulating polystyrene microbeads of 4 and 10 μm diameter through its channel using a voltage of 900 VDC. The particles were separated with efficiencies of 94.0% and 92.5%, respectively. However, roughness in some parts of the channel and connections that had larger diameters compared to the channel created local electric field gradients which, doubtless, hindered separation. It is a promising device that could lead the way toward portable and affordable medical devices.

Dielectrophoresis flow control in microchannels

Abstract The control of flow in microscale is one of the most important problems in microfluidic devices, which in particular, are used as micro heat exchangers. The use of electric field is one of the efficient methods of control of dielectric liquid flow in microscale. The electric field influences liquid flow by the EHD force which affects liquid behaviour in terms of the flow rate and pressure. The EHD force consists of three components: the first is the electrostatic force due to free charges present in the liquid, the next one is the force due to the gradient of permittivity of material, and the third one is caused by the change in the electric field intensity. The EHD force is used also in many commercial devices, for example EHD pumps or dielectrophoretic separators. An own approach to apply the EHD force to control the liquid flow rate is presented in this paper. Authors paid a close attention to the dielectrophoresis effect. Dielectric liquid in a non-uniform electric field tends to drift/migrate towards the region of high electric field intensity. With decreasing the electrode dimensions, the dielectrophoresis force becomes relatively stronger. For the dimensions under 400 μm the dielectrophoresis phenomenon can be used for control and actuation of the liquid flow in microchannels. The originally developed design of such flow controller is presented in this paper. The experimental investigations covered flow rate measurement of 2-propanol in microchannel flow controller with application of AC field. It was showed that the dielectrophoresis phenomenon could effectively control the flow. The results for distilled water are also comparatively discussed in the paper.

A new design for efficient dielectrophoretic separation of cells in a microdevice

Effectiveness of a continuous biological cell separation device can be improved significantly by increasing the distance among different types of cells. To achieve this, most of the recent dielectrophoresis based continuous separation devices implement differential forces on cells either along the transverse direction or the vertical direction with respect to the bulk fluid flow motion. However, interparticle distance can be increased further by implementing forces along both transverse and vertical planes. In this article, a design for a microfluidic platform has been proposed where a new electrode configuration is identified to implement symmetric forces in both vertical and transverse directions. A numerical model, which considers presence of particles in the electric field and flow field, shows a much higher interparticle distance between red blood cells and plasmodium falciparum infected red blood cells in such a device than that in a conventional separation device. This configuration also reduces the possibility of particle trapping on the electrodes, which is a major bottleneck of dielectrophoresis.

Rapid dielectrophoretic characterization of single cells using the dielectrophoretic spring

Dielectrophoresis-based cell separation has significant promise for separation of cells from heterogeneous mixtures based on their electrical properties and is used in diverse areas ranging from hematopoietic stem cell purification to cancer cell isolation. The electrical properties of cells in heterogeneous populations determine if and how well cell subpopulations are separable, and therefore the utility of dielectrophoretic separation is fundamentally determined by our ability to measure electrical properties of cell populations on a cell-by-cell basis. We developed an automated system for electrical characterization of cells that can characterize 1000's of individual cells across a range of conditions (>30 conditions/h). The system uses a continuous-flow microfluidic device and a method termed the dielectrophoretic spring that uses the force balance between dielectrophoresis and fluid drag to measure electrical properties of cells independent of size. We present characterization of the method with beads and cells as well as its application to rapidly find conditions that can discriminate neutrophils with different activation states.

Continuous Cell Separation Using Dielectrophoresis through Asymmetric and Periodic Microelectrode Array

The study presents a dielectrophoretic cell separation method via three-dimensional (3D) nonuniform electric fields generated by employing a periodic array of discrete but locally asymmetric triangular bottom microelectrodes and a continuous top electrode. Traversing through the microelectrodes, heterogeneous cells are electrically polarized to experience different strengths of positive dielectrophoretic forces, in response to the 3D nonuniform electric fields. The cells that experience stronger positive dielectrophoresis are streamed further in the perpendicular direction to the fluid flow, leaving the cells that experience weak positive dielectrophoresis, which continue to traverse the microelectrode array essentially along the laminar flow streamlines. The proposed method has achieved 87.3% pure live cells harvesting efficiency from a live/dead NIH-3T3 cells mixture, and separation of MG-63 cells from erythrocytes with a separation efficiency of 82.8%. The demonstrated cell separation shows promising applications of the DEP separator for cell separation in a continuous mode.

Hybrid gold–copper stamp for rapid fabrication of microchips

Graphical abstractDisplay Omitted Highlights? We have developed simple and low-cost fabrication method of metal stamps. ? The stamps are intended for fast and cheap replication of microfluidic structures. ? Inherent metal hardness allows hundreds of replications in polymer substrate. ? The method is alternative to the expensive methods using synchrotron radiation sources. ? It enables easy separation of final metal stamps from plastic substrate. We have developed a new alternative way for production of hybrid gold-copper stamps intended for fast and cheap replication of microfluidic structures. This novel technique relies on a polydimethylsiloxane (PDMS) casting process, transfer of microstructures into UV curable methyl-methacrylate (MMA) resin and galvanic deposition. The developed method enables an easy separation of fabricated metal stamps from plastic substrate (mechanical separation or wet etching in organic solvents), which favors this method over the metal stamp fabrication directly on SU8 substrate. The fabricated hybrid gold-copper stamps were tested as embossing templates for production of different microstructures. Their functionality was proven in production of microstructures for several applications, e.g., AC electroosmotic micropumps or dielectrophoretic separators.