Dielectrophoretic Field Research Articles

Continuous dielectrophoretic particle separation via isomotive dielectrophoresis with bifurcating stagnation flow.

We present a novel technique for continuous label-free separation of particles based on their dielectrophoretic crossover frequencies. Our technique relies on our unique microfluidic geometry which performs hydrodynamic focusing, generates a stagnation flow with two outlets, and simultaneously produces an isomotive dielectrophoretic field via wall-situated electrodes. To perform particle separation, we hydrodynamically focus particles onto stagnation streamlines and use isomotive dielectrophoretic force to nudge the particles off these streamlines and direct them into appropriate outlets. Focusing particles onto stagnation streamlines obviates the need for large forces to be applied to the particles and therefore increases system throughput. The use of isomotive (spatially uniform) dielectrophoretic force increases system reliability. To guide designers, we develop and describe a simple scaling model for the particle separation dynamics of our technique. The model predicts the range of particle sizes that can be separated as well as the processing rate that can be achieved as a function of system design parameters: channel size, flow rate, and applied potential. Finally, as a proof-of-principle, we use this technique to separate polystyrene bead and cell mixtures of the same diameters as well as mixtures of both particles with varying diameters.

A simple electrical approach to monitor dielectrophoretic focusing of particles flowing in a microchannel.

This paper reports an impedance-based system for the quantitative assessment of dielectrophoretic (DEP) focusing of single particles flowing in a microchannel. Particle lateral positions are detected in two electrical sensing zones placed before and after a DEP-focusing region, respectively. In each sensing zone, particle lateral positions are estimated using the unbalance between the opposite pulses of a differential current signal obtained with a straightforward coplanar electrode configuration. The system is used to monitor the focusing of polystyrene beads of 7 or 10μm diameter, under various conditions of DEP field intensities and flow rates that produce different degrees of focusing. This electrical approach represents a simple and valuable alternative to optical methods for monitoring of particle focusingsystems.

Transverse dielectrophoretic-based DNA nanoscale confinement

Confinement of single molecules within nanoscale environments is crucial in a range of fields, including biomedicine, genomics, and biophysics. Here, we present a method that can concentrate, confine, and linearly stretch DNA molecules within a single optical field of view using dielectrophoretic (DEP) force. The method can convert an open surface into one confining DNA molecules without a requirement for bonding, hydrodynamic or mechanical components. We use a transverse DEP field between a top coverslip and a bottom substrate, both of which are coated with a transparent conductive material. Both layers are attached using double-sided tape, defining the chamber. The nanofeatures lie at the “floor” and do not require any bonding. With the application of an alternating (AC) electric field (2 Vp-p) between the top and bottom electrodes, a DEP field gradient is established and used to concentrate, confine and linearly extend DNA in nanogrooves as small as 100-nm in width. We also demonstrate reversible loading/unloading of DNA molecules into nanogrooves and nanopits by switching frequency (between 10 kHz to 100 kHz). The technology presented in this paper provides a new method for single-molecule trapping and analysis.

Localized Electroporation With Dielectrophoretic Field Flow Fractionation: Toward Removal of Circulating Tumour Cells From Human Blood.

This paper presents the design and experimental performance of a microelectrode-based device to selectively lyse cells in a flow in a microfluidic channel. Localized cell lysis is achieved by utilizing "irreversible electroporation," in which cells are exposed to high magnitude electric pulses. Localized cell lysis in a flow has research applications and may allow for the removal of harmful cells, such as circulating tumor cells from blood. Due to the dependence of this technique on the magnitude of the applied electric field, lethal electric field regions can be localized in the channel by the calibration of the applied voltage. Dielectrophoresis field flow fractionation is used to levitate target cancer cells in the lethal region of the device microchannel. Experiments are performed to demonstrate the localized lysis of MCF7 cancer cells in a mixture of blood cells. Due to their larger size, these circulating tumor cell analogues levitate to a greater height in the channel than erythrocytes. MCF7 lysis is observed to increase from 4.6% in control experiments to 57.3% in active experiments. Leukocyte viability was unaffected in active experiments. These results demonstrate the feasibility of localizing cell lysis in a microfluidic flow environment.

Path of microparticles in a microfluidic device employing dielectrophoresis for hyperlayer field-flow fractionation

This article details the development of a validated dynamic model for predicting the path of microparticles subjected to a dielectrophoretic field, on a microfludic device, for hyperlayer field flow fractionation; the model is subsequently used for parametric study. The electrode configuration consists of multiple finite sized electrodes placed on the bottom surface of the microchannel and an infinitely long electrode located on the top surface of the same microchannel. The model consists of two sets of equations; the first set deals with the electrical parameters inside the microchannel while the second set describes the microparticle's motion inside the microchannel. The governing equations describing the path of microparticles are based on Newton's second law and depend on geometric and operating parameters including microparticle radius, actuation voltage, microchannel height, volumetric flow rate, and electrode/gap length. The influence of the forces due to gravity, buoyancy, drag, virtual mass, and dielectrophoresis are included in the equations of motion. The path of the microparticle consists of two phases--transient and steady state. During the transient phase all parameters are influential. The steady state vertical displacement is dependent on microchannel height, actuation voltage, and electrode/spacing length and independent of microparticle radius and volumetric flow rate above a threshold value. Steady state levitation does not exist when the volumetric flow rate is below its threshold.

439 Comparison of Dielectrophoretic Field Flow Fractionation (DEP-FFF) with ApoStream™, an Antibody Independent Platform, with Immunomagnetic Capture Using CellSearch™ for Enumeration of Circulating Tumor Cells in Patients with Metastatic Prostate Cancer

439 Comparison of Dielectrophoretic Field Flow Fractionation (DEP-FFF) with ApoStream™, an Antibody Independent Platform, with Immunomagnetic Capture Using CellSearch™ for Enumeration of Circulating Tumor Cells in Patients with Metastatic Prostate Cancer

Rapid detection of cancer-related cfc-DNA biomarkers directly from whole blood.

14 Background: We have developed a “Sample to Answer” dielectrophoretic (DEP) technology for detecting cancer and other disease-related cfc-DNA biomarkers directly from whole blood. Using AC/DC electric field microarray devices specifically designed for the isolation of cfc-DNA, exosomes and cellular nanoparticulates from blood samples, experiments were carried out by adding about 20ul of the patient blood sample to the DEP microarray device. Methods: The DEP field was applied at 10 kHz and 20 Vp-p for 15 minutes to nine microelectrodes. The microarray was then washed three times with 0.5x PBS with the DEP field on, and finally examined by epifluorescent microscopy. Results: For Chronic Lymphocytic Leukemia (CLL) cancer patient blood samples, results clearly show greenish white fluorescent circles around the nine DEP microelectrodes on the array. This is the SYBR Green fluorescent stained cfc-DNA from the CLL cancer patient blood sample now concentrated in the DEP high field regions. Normal blood samples show little or no fluorescence around the DEP high field microelectrodes. More than fifty CLL samples have been analyzed to date. Conclusions: DEP devices are now being used to collect cfc-DNA from other cancer patient whole blood, plasma and serum samples. Blood sample to PCR is now achieved in less than twenty minutes. Newer work has demonstrated that PCR can be carried out in-situ (in the same device). Thus, the new DEP technology and devices set the stage for “seamless sample to answer” diagnostic systems which will allow a variety of important cancer and other disease biomarkers to be rapidly isolated and analyzed directly from whole blood and other clinical samples.

Aligned MWCNT-Reinforced Bulk Epoxy-Matrix Composites by Dielectrophoretic Force

Studies have proved that enhancing epoxy matrices by adding carbon nanotubes to form structural reinforcements has significantly improved mechanical properties at very low carbon nanotube loading. That mechanical properties of aligned composites are better than those of random ones has been demonstrated in past studies; however, alignment is not easy to achieve in carbon nanotube epoxy-matrix bulk composite by conventional techniques. In this study, epoxy-matrix bulk composites reinforced by aligned multi-walled carbon nanotubes (MWCNTs) are prepared using an RF electric field to elicit dipolar interactions among the nanotubes in a viscous matrix following immobilization by curing under continuous application of an anisotropic electric field and the fracture toughness is experimentally characterized later. The processes of actively aligned MWCNTs epoxy-matrix bulk composite were controlled as a function of CNT weight fraction, the frequency of dielectrophoretic field and processing time. Carbon nanotubes are not only aligned along the field but also migrate laterally to enhance thickness. Eventually, addition of nanotubes improved the mechanical properties of the MWCNT/epoxy bulk composites, and the increase in the flexural modulus and fracture toughness with the aligned nanotube composite is two times greater than the improvement for the randomly oriented composite.

Using a Microfluidic–Microelectric Device to Directly Separate Serum/Blood Cells from a Continuous Whole Bloodstream Flow

To make the rapid separation of serum/blood cells possible in a whole bloodstream flow without centrifugation and Pasteur pipette suction, the first step is to use a microchannel to transport the whole bloodstream into a microdevice. Subsequently, the resulting serum/blood cell is separated from the whole bloodstream by applying other technologies. Creating the serum makes this subsequent separation possible. To perform the actual separation, a microchannel with multiple symmetric curvilinear microelectrodes has been designed on a glass substrate and fabricated with micro-electromechanical system technology. The blood cells can be observed clearly by black-field microscopy imaging. A local dielectrophoretic (DEP) force, obtained from nonuniform electric fields, was used for manipulating and separating the blood cells from a continuous whole bloodstream. The experimental studies show that the blood cells incur a local dielectrophoretic field when they are suspended in a continuous flow (v = 0.02–0.1 cm/s) and exposed to AC fields at a frequency of 200 kHz. Using this device, the symmetric curvilinear microelectrodes provide a local dielectrophoretic field that is sufficiently strong for separating nearby blood cells and purifying the serum in a continuous whole bloodstream flow.

Highly controlled electrofusion of individually selected cells in dielectrophoretic field cages

The prospect of novel therapeutic approaches has renewed the current interest in the fusion of rare cells, like stem cells or primary immune cells. While conventional techniques are only capable of mass fusion, lab-on-a-chip systems often still lack an acceptable method for making the cells available after processing. Here, we present a microfluidic approach for electrofusion on the single-cell level that offers high control over the cells both before and after fusion. For cell pairing and fusion, we employed dielectrophoresis and AC voltage pulses, respectively. Each cell has been characterized and selected before they were paired, fused and released from the fluidic system for subsequent analysis and cultivation. The successful experimental evaluation of our system was further corroborated by numerical simulations. We obtained fusion efficiencies of more than 30% for individual pairs of mouse myeloma and B cell blasts and showed the proliferating ability of the hybrid cells 3 d after fusion. Since aggregates of more than two cells can be fused, the technique could also be developed further for generating giant cells for low-noise electrophysiology in the context of semi-automated pharmaceutical screening procedures.

Using Chelating Chitosan Nanobeads and a Microfluidic–Microelectric Trap to Sort Lead(II) in a Continuous Bloodstream Flow

The sorting of ions in a bloodstream flow has been carried out by mixing the ions in a chitosan nanobeads aqua-solution and then using a chelating mechanism to selectively sponge them up. To obtain an efficient chelating reaction and chelating nanobeads that can be attracted and separated from the bloodstream flow, a microfluidic device that has a microchannel with electrodes has been designed and fabricated by a microelectromechanical process. A local dielectrophoretic force obtained from nonuniform electric fields was elected to manipulate the chelating nanobeads in a continuous bloodstream flow. The experimental studies indicate that the chelating nanobeads undergo a positive dielectrophoresis when suspended in a continuous flow and exposed to radio frequency/ac fields at frequency. In this device, the microchannel with electrodes provides a local dielectrophoretic field that is strong enough to manipulate and separate the chelating nanobeads in a continuous bloodstream flow.

High-throughput electrokinetic bioparticle focusing based on a travelling-wave dielectrophoretic field

This study presents a sheathless and portable microfluidic chip that is capable of high-throughput focusing bioparticles based on 3D travelling-wave dielectrophoresis (twDEP). High-throughput focusing is achieved by sustaining a centralized twDEP field normal to the continuous through-flow direction. Two twDEP electrode arrays are formed from upper and lower walls of the microchannel and extend to its center, which induce twDEP forces to provide the lateral displacements in two directions for focusing the bioparticles. Bioparticles can be focused to the center of the microchannel effectively by twDEP conveyance when the characteristic time due to twDEP conveying in the y direction is shorter than the residence time of the particles within twDEP electrode array. Red blood cells can be effectively focused into a narrow particle stream (~10 μm) below a critical flow rate of 10 μl/min (linear flow velocity ~5 mm/s), when under a voltage of 14 Vp–p at a frequency of 500 kHz is applied. Approximately 90% focusing efficiency for red blood cells can be achieved within two 6-mm-long electrode arrays when the flow rate is below 12 μl/min. Blood cells and Candida cells were also focused and sorted successfully based on their different twDEP mobilities. Compared to conventional 3D-paired DEP focusing, velocity is enhanced nearly four folds of magnitude. 3D twDEP provides the lateral displacements of particles and long residence time for migrating particles in a high-speed continuous flow, which breaks through the limitation of many electrokinetic cell manipulation techniques.

Size based separation of microparticles using a dielectrophoretic activated system

This work describes the separation of polystyrene microparticles suspended in deionized (DI) water according to their dimensions using a dielectrophoretic (DEP) system. The DEP system utilizes curved microelectrodes integrated into a microfluidic system. Microparticles of 1, 6, and 15 μm are applied to the system and their response to the DEP field is studied at different frequencies of 100, 200, and 20 MHz. The microelectrodes act as a DEP barrier for 15 μm particles and retain them at all frequencies whereas the response of 1 and 6 μm particles depend strongly on the applied frequency. At 100 kHz, both particles are trapped by the microelectrodes. However, at 200 kHz, the 1 μm particles are trapped by the microelectrodes while the 6 μm particles are pushed toward the sidewalls. Finally, at 20 MHz, both particles are pushed toward the sidewalls. The experiments show the tunable performance of the system to sort the microparticles of various dimensions in microfluidic systems.

Effect of a blind spot in a dielectrophoretic field on the separation of human breast cancer cells (MCF 7)

Previously, we proposed a ‘dielectrophoretically activated cell sorting’ (DACS) system, which can be applied to the separation of various cells without labeling them with magnetic or fluorescent materials. By using a specific frequency range, it was verified that the dielectric material properties of cells can be exploited in order to collect target cells from a cell mixture. However, because about 20% of the error in separation efficiencies was always detected, it became a subject to investigate. Therefore, we assumed that variance in cell size might be responsible for the errors. By measuring the diameter of human breast cancer cells (MCF 7) and classifying separation efficiencies according to diameter, it was verified that the errors in separation efficiency are affected by cell size. Moreover, the existence of a ‘blind spot,’ i.e., a space with weak force within the dielectrophoretic field generated by a pair of electrodes, was proven by commercial code CFD-ACE+®. With simulation and experimental results, we demonstrated that some efficiency errors occur because small sized cells (between 15 and 20 μm) pass through the ‘blind spot’.

Using Dielectrophoresis to Trap Nanobead/Stem Cell Compounds in Continuous Flow

To make the selective sorting of target cells in a multicomponent solution possible, the first step is to use an antigen–antibody reaction to attach antibody-immobilized nanobeads to the surfaces of target stem cells. Later, the resulting nanobead/stem cell compounds are trapped and separated from the mixture by applying other technologies. Creating the compounds makes this subsequent separation possible. To effect the actual separation, a microchannel with multiple electric strips is designed on a silicon substrate and is fabricated with the microelectromechanical systems technology. A local dielectrophoretic force, obtained from nonuniform electric fields, is used to manipulate and trap the compounds in a continuous flow. The experimental studies show that the compounds incur a local dielectrophoretic field when they are suspended in a continuous flow and are exposed to ac fields at a 500 kHz frequency. Using this device, the strip electrodes provide a local dielectrophoretic field strong enough to manipulate and attract nearby compounds in a continuous flow.

Dielectrophoretic characterization of erythrocytes: Positive ABO blood types

Dielectrophoretic manipulation of erythrocytes/red blood cells is investigated as a tool to identify blood type for medical diagnostic applications. Positive blood types of the ABO typing system (A+, B+, AB+ and O+) were tested and cell responses quantified. The dielectrophoretic response of each blood type was observed in a platinum electrode microdevice, delivering a field of 0.025V(pp)/microm at 1 MHz. Responses were recorded via video microscopy for 120 s and erythrocyte positions were tabulated at 20-30 s intervals. Both vertical and horizontal motions of erythrocytes were quantified via image object recognition, object tracking in MATLAB, binning into appropriate electric field contoured regions (wedges) and statistical analysis. Cells of O+ type showed relatively attenuated response to the dielectrophoretic field and were distinguished with greater than 95% confidence from all the other three blood types. AB+ cell responses differed from A+ and B+ blood types likely because AB+ erythrocytes express both the A and B glycoforms on their membrane. This research suggests that dielectrophoresis of untreated erythrocytes beyond simple dilution depends on blood type and could be used in portable blood typing devices.

Simulations of a dielectrophoretic membrane filtration process for removal of water droplets from water-in-oil emulsions

A novel separation technique based on simultaneous application of AC dielectrophoresis and preferential transport through a semipermeable hydrophilic membrane is proposed for separation of small amounts of emulsified water droplets from a water-in-oil emulsion. Embedding an array of parallel microelectrodes on a membrane matrix, followed by application of an AC potential to these electrodes, can result in capturing the water droplets onto the membranes from the emulsion during a crossflow filtration process. The present paper describes the theoretical principles underlying such a process, and describes a simple mathematical framework based on trajectory analysis for assessing the separation efficiency of such a technique. The results indicate that superimposition of an AC dielectrophoretic field can significantly enhance the preferential transport of the emulsified water through the membrane in a crossflow filtration device. This can lead to a highly efficient continuous separation process for dilute emulsions.

Numerical solution of the dielectrophoretic and travelling wave forces for interdigitated electrode arrays using the finite element method

AC electrokinetics is the study of the movement of polarisable particles under the influence of AC electric fields. The fields are applied to a suspension of particles by planar microelectrode structures and one particular design, the interdigitated bar electrode has been used in both dielectrophoretic (DEP) field flow fractionation and travelling wave dielectrophoresis. This paper presents, numerical solutions of the DEP and travelling wave forces for an interdigitated electrode array energised with either a 2- or 4-phase signal. The electrorotational torque experienced by the particle in the 4-phase travelling wave array is also calculated. The solutions are compared with previous results.

Flow fractionation of microparticles under a dielectrophoretic field in a quadrupole electrode capillary.

A technique of fractionation for microparticles was proposed that utilized a unique combination of a dielectrophoretic (DEP) field generated by a quadrupole electrode and a laminar flow in a capillary of 82.5 microm in radius. The fabricated capillary possessed four platinum wires in its inside wall as a quadrupole electrode. In a nonuniform electric field generated by the quadrupole electrode, microparticles, such as polystyrene and carbon, in water experienced DEP forces in the radial direction. When a sample solution was pumped in, an ideal laminar flow perpendicular to the DEP force was formed inside the capillary. The microparticles dynamically migrated by the DEP force across the laminar flow while they were carried by the flow. A theoretical model taking the DEP force and the laminar flow pattern into account predicted the elution profiles of the single microparticles quantitatively. The elution times of the microparticles depended on the dielectric properties and the sizes of the microparticles, as well as the voltage and frequency of the applied alternating current.

The dielectrophoretic and travelling wave forces generated byinterdigitated electrode arrays: analytical solution using Fourierseries

In alternating current electrokinetics, electric fields are used togenerate forces on particles. Techniques have been applied for themanipulation of particles and the measurement of their dielectric properties.The fields are typically generated by microelectrode structures fabricated onplanar surfaces. One particular design, using interdigitated bar electrodes,is used both in dielectrophoretic field flow fractionation and travelling wavedielectrophoresis. This paper presents a Fourier series analysis of thedielectrophoretic force on a particle generated by this type of electrodearray, for both dielectrophoresis and travelling wave dielectrophoresis.Simple expressions are derived for the force at a distance of the order of theelectrode spacing from the electrodes. A full analytical expression is givenfor the dielectrophoretic force in two dimensions. Comparisons are made withpreviously published experimental observations.