Dielectrophoresis

The distribution of electric field for the alignment and attachment of carbon nanotubes (CNTs) was simulated. To be attached at the desired place, the aligned and attracted CNTs should be stayed in the desired area called the stable region or the quasi-stable region for an instant where the change of electric field is minimized. Since the conical electrode has the very narrow sized quasi-stable region, few CNTs can be attached. The rectangular electrodes have a wide stable region, so lots of CNTs can be attached. The results indicate that the round electrode which has a proper sized quasi-stable region is more effective for aligning and attaching a single CNT than the conical or rectangular shaped electrodes.

Fast immobilization of probe beads by dielectrophoresis-controlled adhesion in a versatile microfluidic platform for affinity assay The use of probe beads for lab-on-chip affinity assays is very interesting from a practical point of view. It is easier to handle and trap beads than molecules in microfluidic systems. We present a method for the immobilization of probe beads at defined areas on a chip using dielectrophoresis (DEP)-controlled adhesion. The method is fast, i.e., it takes between 10 and 120 s-depending on the protocol-to functionalize a chip surface at defined areas. The method is versatile, i.e., it works for beads with different types of probe molecule coatings. The immobilization is irreversible, i.e., the retained beads are able to withstand high flow velocities in a flow-through device even after the DEP voltage is turned off, thus allowing the use of conventional high-conductivity analyte buffers in the following assay procedure. We demonstrate the on-chip immobilization of fluorescent beads coated with biotin, protein A, and goat-antimouse immunoglobulin G (IgG). The number of immobilized beads at an electrode array can be determined from their fluorescence signal. Further, we use this method to demonstrate the detection of streptavidin and mouse IgG. Finally, we demonstrate the feasibility of the parallel detection of different analyte molecules on the same chip.

An experimental and theoretical study is described concerning the dielectric motion of particles in a suspension subject to high-gradient AC electric fields. The experiments were performed on very dilute suspensions of polystyrene latex heads in DI water.

Affinity binding is the principle used in a large number of bio-assays. Aside from specific bindings, nonspecific bindings usually deteriorate assays by giving false positive signals and restrict the detection limit. Currently, the assay specificity is mainly dependent on the effectiveness of a suitable surface chemistry. We report an approach to discriminate specific and non-specific bindings with dielectrophoretic (DEP) forces for on-chip magnetic bio-assays. Conjugated to the analytes, magnetic particles were used as the agents for DEP force generation. Due to a weaker binding strength, the non-specifically bound particles were removed while specific bindings remained intact. Analytical and finite element calculations were also performed to study all relevant forces. Furthermore, the removal of magnetic particles was also assessed by measuring the magnetic signal using magnetoresistive sensors. This technique can not only be used to improve the specificity of the on-chip bio-assays but also be developed as a tool of force spectroscopy for the study of bio-molecular binding physics.

The technology for electrostatic enhancement of coalescence of water droplets in oil emulsions is critically reviewed. Historically, the electrostatic coalescer was invented for the petroleum-related industries in California [US Patent 987 115 (1911)]. Nowadays, this technology is generally considered for the separation of an aqueous phase dispersed in a dielectric oil phase with a significantly lower dielectric constant than that of the dispersed phase. Various designs have been introduced, with most using alternating current (AC) electric fields with mains frequency (50 or 60 Hz). The direct current (DC) electric field has been less common in the past as compared to the AC. In 1981, the concept of pulsed DC electric fields was introduced, together with insulated electrodes [Trans. IChemE 59 (1981) 229-237; UK Patent 217 1031A (1986)]. Since then, this has become more common in the electrocoalescence technology. Pulsed DC and AC fields are especially useful, when the aqueous phase content of the emulsion is high, to prevent short-circuiting between the pair of electrodes. Processing of oil from old wells is a good example, where the volumetric water content could vary significantly. Reported work by some workers indicates the existence of an optimum frequency, which depends on the electrode coating material, its thickness and the liquid emulsion composition. This is however, a contentious issue which has not been completely resolved. The characteristics and geometry of the electrode system (generally cylindrical or plate) influence the performance of the electrostatic coalescer, and are closely related to the type of the applied electric field and the emulsion used. There are basically two types of electrode: uninsulated electrode and insulated electrode. Combination of electrocoalescence and mechanical separation (e.g., centrifugal force) has also been introduced. Heating and the addition of chemicals have been shown to further enhance the electrocoalescence of water droplets. Other methods that can be combined with the electrical treatment are filtration, methods employing high pressure and temperature, and mixing. This review paper also looks at some of the current specific industrial applications using the electrocoalescence technology. Besides the oil and petroleum industries, this technology has potential applications in the edible oil industries such as palm oil, sunflower oil and vegetable oil processing. Most of the currently available equipment is very big and bulky, having a large inventory of emulsion. Therefore, we see the future trend for new developments to be in the direction of inventing small portable devices, incorporating features such as optimum electric fields and combined electrical and centrifugal forces to further enhance the separation of water-in-oil emulsions. Furthermore, a better understanding of the fundamentals of electrocoalescence will enable a better design of the geometry of the electrodes, of the flow field with respect to the electric fields, the type of dispersion used and the type of the applied electric field.

This paper reviews the current understanding of electrocoalescence of water droplets in oil, highlighting particularly the mechanisms proposed for droplet–droplet and droplet–interface coalescence under the influence of an applied electric field, as well as various factors influencing the ...

Calculations of resultant electrostatic force on a charged spherical or cylindrical capacitor with two sectors of different dielectrics, based on the classical formulas of electrostatic pressure, Kelvin polarization force density, and Maxwell stress tensor predict a reactionless force that violates Newton’s 3rd law. Measurements didn’t confirm the existence of such a reactionless thrust, thus there is an apparent inconsistency in the classical EM theory that leads to wrong results.

Measurements of dielectrophoretic collection spectra of Escherichia coli and Staphylococcus aureus suspensions are used for obtaining dielectric characteristics of both types of bacteria. The experiments are interpreted using a numerical method that models the cells as compartmented spherical or rod-like particles. We show the usefulness of this simple method to extract significant information about the electrical properties of Gram-negative and -positive bacteria.

This paper analyzes the forces, including the Stokes drag force induced by the electrothermal flow, imposed on the particles in conventional dielectrophoresis in microchannels with interdigitated electrodes through a two-dimensional mathematical model. The conditions for the positive and negative dielectrophoresis are revealed. The electrical field, the magnitude of the negative dielectrophoretic force and Stokes drag force are presented. The levitation heights for particles at different horizontal positions with and without considering the Stokes drag force are compared, and the effect of the particle radius for the levitation height is also analyzed.

Colloidal particles suspended in water respond to direct (DC) or alternating current (AC) fields in a variety of ways, including directional motion along or across the field direction, field-gradient dependent response and induced particle-particle interaction. We review here some of these effects and their applications in new techniques for particle manipulation and assembly, making of novel biomaterials and designing of new self-propelling microdevices. The coupling of the counterionic layer mobility, fluid flows and the resulting particle motion are the basis not only of the classic electrophoretic effects, but also of the recent developments in AC electrohydrodynamics and induced charge electrophoresis of asymmetric particles. We also discuss how dielectrophoresis (particle interaction with external AC field gradients), could be used to manipulate and assemble objects on any size scale. We discuss the interactions leading to the assembly of such structures, ways to simulate the dynamics of the process and the effect of particle size and conductivity on the type of structure obtained. Finally, we demonstrate how an additional level of complexity can be engineered to turn miniature semiconductor diodes into prototypes of self-propelling micromachines and micropumps. The diodes suspended in water propel themselves electro-osmotically when a uniform alternating electric field is applied across the container. Semiconductor diodes embedded in channel walls could serve as distributed microfluidic pumps and mixers powered by a global external field.

The possibility of using novel architectures based on carbon nanotubes (CNTs) for a realistic monitoring of
the air quality in an urban environment requires the capability to monitor concentrations of polluting gases
in the low-ppb range. This limit has been so far virtually neglected, as most of the testing of new ammonia
gas sensor devices based on CNTs is carried out above the ppm limit. In this paper, we present single-wall
carbon nanotube (SWCNT) chemiresistor gas sensors operating at room temperature, displaying an
enhanced sensitivity to NH3. Ammonia concentrations in air as low as 20 ppb have been measured, and
a detection limit of 3 ppb is demonstrated, which is in the full range of the average NH3 concentration
in an urban environment and well below the sensitivities so far reported for pristine, non-functionalized
SWCNTs operating at room temperature. In addition to careful preparation of the SWCNT layers,
through sonication and dielectrophoresis that improved the quality of the CNT bundle layers, the lowppb
limit is also attained by revealing and properly tracking a fast dynamics channel in the desorption
process of the polluting gas molecules.

Dielectrophoresis ͑DEP͒ is employed to differentiate clones of mouse melanoma B16F10 cells. Five clones were tested on microelectrodes. At a specific excitation frequency, clone 1 showed a different DEP response than the other four. Growth rate, melanin content, recovery from cryopreservation, and in vitro invasive studies were performed. Clone 1 is shown to have significantly different melanin content and recovery rate from cryopreservation. This paper reports the ability of DEP to differentiate between two malignant cells of the same origin. Different DEP responses of the two clones could be linked to their melanin content.

The topic of this dissertation is embedded into the newborn field of inorganic nanowires. The research was focused on zinc oxide (ZnO) nanowires, in particular, which besides posing fundamental questions in physics, promise broad range of applications. ZnO nanowires were grown by chemical-vapour-deposition (CVD) using the vapour-liquid-solid (VLS) mechanism with gold particles as catalysts. Oxygen was introduced in the argon carrier gas and zinc was carboreduced from the ZnO/C mixture. We produced micrometer long ZnO nanowires and their diameter was controlled by the size of the gold catalyst particles. The 6. Conclusion.

Miniaturization to the micrometer and nanometer scale opens up the possibility to probe biology on a length scale where fundamental biological processes take place, such as the epigenetic and genetic control of single cells. To study single cells the necessary devices need to be integrated on a single chip; and, to access the relevant length scales, the devices need to be designed with feature sizes of a few nanometers up to several micrometers. We will give a few examples from the literature and from our own research in the field of miniaturized chip-based devices for DNA analysis, including dielectrophoresis for purification of DNA, artificial gel structures for rapid DNA separation, and nanofluidic channels for direct visualization of single DNA molecules. The length scales of the fundamental building blocks of biology overlap with the length scales realizable using micro-and nanofabrication technology from the microelectronics industry. The persistence length (L p ) of DNA is given for standard physiological conditions. The gene size corresponds to the typical size of 1 kbp excluding any non-coding regions (introns). The chromosome size range corresponds to metaphase condensed chromosomes. The radius of gyration is indicated for DNA molecules ranging in size from 100 kbp to 100 Mbp C.

Calculations of resultant electrostatic force on a charged spherical or cylindrical capacitor with two sectors of different dielectrics, based on the classical formulas of electrostatic pressure, Kelvin polarization force density, and Maxwell stress tensor predict a reactionless force that violates Newton's 3rd law. Measurements didn't confirm the existence of such a reactionless thrust, thus there is an apparent inconsistency in the classical EM theory that leads to wrong results.

A review is presented of the present status of the theory, the developed technology and the current applications of dielectrophoresis ͑DEP͒. Over the past 10 years around 2000 publications have addressed these three aspects, and current trends suggest that the theory and technology have matured sufficiently for most effort to now be directed towards applying DEP to unmet needs in such areas as biosensors, cell therapeutics, drug discovery, medical diagnostics, microfluidics, nanoassembly, and particle filtration. The dipole approximation to describe the DEP force acting on a particle subjected to a nonuniform electric field has evolved to include multipole contributions, the perturbing effects arising from interactions with other cells and boundary surfaces, and the influence of electrical double-layer polarizations that must be considered for nanoparticles. Theoretical modelling of the electric field gradients generated by different electrode designs has also reached an advanced state. Advances in the technology include the development of sophisticated electrode designs, along with the introduction of new materials ͑e.g., silicone polymers, dry film resist͒ and methods for fabricating the electrodes and microfluidics of DEP devices ͑photo and electron beam lithography, laser ablation, thin film techniques, CMOS technology͒. Around three-quarters of the 300 or so scientific publications now being published each year on DEP are directed towards practical applications, and this is matched with an increasing number of patent applications. A summary of the US patents granted since January 2005 is given, along with an outline of the small number of perceived industrial applications ͑e.g., mineral separation, micropolishing, manipulation and dispensing of fluid droplets, manipulation and assembly of micro components͒. The technology has also advanced sufficiently for DEP to be used as a tool to manipulate nanoparticles ͑e.g., carbon nanotubes, nano wires, gold and metal oxide nanoparticles͒ for the fabrication of devices and sensors. Most efforts are now being directed towards biomedical applications, such as the spatial manipulation and selective separation/enrichment of target cells or bacteria, high-throughput molecular screening, biosensors, immunoassays, and the artificial engineering of three-dimensional cell constructs. DEP is able to manipulate and sort cells without the need for biochemical labels or other bioengineered tags, and without contact to any surfaces. This opens up potentially important applications of DEP as a tool to address an unmet need in stem cell research and therapy.

This study reports a new microfluidic chip capable of delivering and pre-positioning cells in a predefined trapping zone, and followed by manipulation of buried optical fibers for on-chip, dual-beam, optical trapping and stretching. In this microfluidic system, microchannels, micropumps, microvalves, dielectrophoretic (DEP) electrodes and active fiber manipulators were fabricated and integrated using micro-electro-mechanical-systems technology to perform several crucial functions including transportation, pre-positioning and manipulation of cells. Experimental results showed that by integrating three micropumps connected in series, the cell samples were automatically delivered into the flow focusing area and then transported to the trapping zone. A single cell can be confined by microvalves and then elevated towards the optical trapping zone by a negative-DEP force operated at a low voltage (20 V p-p ) and at a specific frequency (900 kHz). The active fiber manipulators can be used for optical trapping, manipulation, and stretching. A red blood cell was successfully trapped and stretched by a dual-beam, optical trap using the proposed microfluidic system. The developed system is promising for further applications that require trapping, manipulation and biomechanical analysis of a single cell or particle.

Dielectrophoresis can discriminate distinct cellular identities in heterogeneous populations, and monitor cell state changes associated with activation and clonal expansion, apoptosis, and necrosis, without the need for biochemical labels. Demonstrated capabilities include the enrichment of haematopoetic stem cells from bone marrow and peripheral blood, and adult stem cells from adipose tissue. Recent research suggests that this technique can predict the ultimate fate of neural stem cells after differentiation before the appearance of specific cell-surface proteins. This review summarises the properties of cells that contribute to their dielectrophoretic behaviour, and their relevance to stem cell research and translational applications.

We present a novel, on-chip system for the electrokinetic capture of bacterial cells and their identification using the polymerase chain reaction (PCR). The system comprises a glass-silicon platform with a set of micro-channels, -chambers, and -electrodes. A platinum thin film resistor, placed in the proximity of the chambers, is used for temperature monitoring. The whole chip assembly is mounted on a Printed Circuit Board (PCB) and wire-bonded to it. The PCB has an embedded heater that is utilized for PCR thermal cycle and is controlled by a Lab-View program. Similar to our previous work, one set of electrodes on the chip inside the bigger chamber (0.6 ll volume) is used for diverting bacterial cells from a flowing stream into to a smaller chamber (0.4 nl volume). A second set of interdigitated electrodes (in smaller chamber) is used to actively trap and concentrate the bacterial cells using dielectrophoresis (DEP). In the presence of the DEP force, with the cells still entrapped in the micro-chamber, PCR mix is injected into the chamber. Subsequently, PCR amplification with SYBR Green detection is used for genetic identification of Listeria monocytogenes V7 cells. The increase in fluorescence is recorded with a photomultiplier tube module mounted over an epifluorescence microscope. This integrated micro-system is capable of genetic amplification and identification of as few as 60 cells of L. monocytogenes V7 in less than 90 min, in 600 nl volume collected from a sample of 10 4 cfu ml −1 . Specificity trials using various concentrations of L. monocytogenes V7, Listeria innocua F4248, and Escherichia coli O157:H7 were carried out successfully using two different primer sets specific for a regulatory gene of L. monocytogenes, prfA and 16S rRNA primer specific for the Listeria spp., and no cross-reactivity was observed.

MEMS, Electromagnetic field is a way to manipulate droplets, beads or cells without direct contact. In particular, dielectrophoresis is often used in BioMEMS applications, for cell handling operations such as moving, sorting, trapping or deforming cells. In this paper, a 3D focusing geometry for the electrical field is proposed, that permit the trapping of single cell, or cells pair, thanks to positive dielectrophoresis. The design is explained with highlighting the focusing effect versus insulator shape for trapping cells. A prototype based on classical MEMS process and results of first trapping are presented.

Effects of imposed DC electric fields on microbubble growth generated from a rectangular Pt microheater (140 Â 100 lm) fabricated on one wall of the microchannel under pulse heating are investigated experimentally in this paper. Bubble dynamics and surface temperature response of the microheater during pulse heating are observed and recorded using a high speed CCD and data acquisition system. Measurements of nucleation time and nucleation temperature and heat flux at boiling inception are taken at a fixed flow rate of 0.6 ml/min and pulse width of 1 ms, and with the electric field strength gradually increasing from zero. With increasing electric field strength, it is found that heat flux required for boiling inception is increased, boiling nucleation time is delayed, and nucleation temperature is reduced. Bubble growth is suppressed by the inward dielectrophoresis force acting at the vapor/water interface which is induced by the electric field. As a result, the diameter of the bubble becomes smaller, and the interface instability is suppressed during the bubble growth period. In addition, it is found that multiple nucleate sites appear on the surface of the micro-heater at high heat flux when the electric field is increased to a sufficiently high strength. A map showing regimes of single and multi nucleate sites in a plot of heat flux versus electric field strength is obtained.

Dielectrophoresis (DEP) is a nondestructive electrokinetic mechanism with great potential for the manipulation of bioparticles. DEP is the movement of particles induced by polarization effects in nonuniform electric fields. Since the 1960s, this technique has been successfully used for the manipulation of microbioparticles, such as microorganisms. Moreover, due to the advances in microfabrication techniques, that allowed progressively smaller microstructures to be constructed, DEP can now be used for the manipulation of nanobioparticles. The first research studies on the DEP of nanobioparticles started in the 1990s. Since then, many research groups have carried out outstanding work with DEP of nanobioparticles such as macromolecules, virus, and spores. However, the need of a critical report that integrates these findings is evident. The aim of the present review is to depict the state-of-the-art on the use of DEP for the separation of nanobioparticles and the potential trends of novel applications of this technique. This review compiles and analyzes the significant findings obtained by many researchers. This publication is intended to provide the reader with state-of-the-art information on many research studies focused on DEP to handle nanobioparticles.

A numerical investigation of the mechanism by which viral particles suspended in physiologically relevant (i.e., high ionic strength) media can be electrokinetically sampled on a surface is presented. Specifically, sampling of virus from a droplet is taking place by means of a high frequency non-uniform electric field, generated by energized planar quadrupolar microelectrodes deposited on an oxidized silicon chip. The numerical simulations are based on experimental conditions applied in our previous work with vesicular stomatitis virus. A 3D computer model is used to yield the spatial profiles of electric field intensity, temperature, and fluid velocity inside the droplet, as well as the force balance on the virus. The results suggest that rapid virus sampling can be achieved by the synergistic action of dielectrophoresis and electrothermal fluid flow. Specifically, electrothermal fluid flow can be used to transport the virus from the bulk of a sample to the surface, where dielectrophoretic forces, which become significant only at very small length scales away from the surface, can cause its stable capture.

We have successfully demonstrated selective trapping, concentration, and release of various biological organisms and inert beads by insulator-based dielectrophoresis within a polymeric microfluidic device. The microfluidic channels and internal features, in this case arrays of insulating posts, were initially created through standard wet-etch techniques in glass. This glass chip was then transformed into a nickel stamp through the process of electroplating. The resultant nickel stamp was then used as the replication tool to produce the polymeric devices through injection molding. The polymeric devices were made of Zeonor ® 1060R, a polyolefin copolymer resin selected for its superior chemical resistance and optical properties. These devices were then optically aligned with another polymeric substrate that had been machined to form fluidic vias. These two polymeric substrates were then bonded together through thermal diffusion bonding. The sealed devices were utilized to selectively separate and concentrate a biological pathogen simulants. These include spores that were selectively concentrated and released by simply applying D.C. voltages across the plastic replicates via platinum electrodes in inlet and outlet reservoirs. The dielectrophoretic response of the organisms is observed to be a function of the applied electric field and post size, geometry and spacing. Cells were selectively trapped against a background of labeled polystyrene beads and spores to demonstrate that samples of interest can be separated from a diverse background. We have implemented and demonstrated here a methodology to determine the concentration factors obtained in these devices.

Efficient and robust particle separation and enrichment techniques are critical for a diverse range of lab-on-a-chip analytical devices including pathogen detection, sample preparation, high-throughput particle sorting, and biomedical diagnostics. Previously, using insulatorbased dielectrophoresis (iDEP) in microfluidic glass devices, we demonstrated simultaneous particle separation and concentration of various biological organisms, polymer microbeads, and viruses. As an alternative to glass, we evaluate the performance of similar iDEP structures produced in polymer-based microfluidic devices. There are numerous processing and operational advantages that motivate our transition to polymers such as the availability of numerous innate chemical compositions for tailoring performance, mechanical robustness, economy of scale, and ease of thermoforming and mass manufacturing. The polymer chips we have evaluated are fabricated through an injection molding process of the commercially available cyclic olefin copolymer Zeonor 1060R. This publication is the first to demonstrate insulator-based dielectrophoretic biological particle differentiation in a polymeric device injection molded from a silicon master. The results demonstrate that the polymer devices achieve the same performance metrics as glass devices. We also demonstrate an effective means of enhancing performance of these microsystems in terms of system power demand through the use of a dynamic surface coating. We demonstrate that the commercially available nonionic block copolymer surfactant, Pluronic F127, has a strong interaction with the cyclic olefin copolymer at very low concentrations, positively impacting performance by decreasing the electric field necessary to achieve particle trapping by an order of magnitude. The presence of this dynamic surface coating, therefore, lowers the power required to operate such devices and minimizes Joule heating. The results of this study demonstrate that iDEP polymeric microfluidic devices with surfactant coatings provide an affordable engineering strategy for selective particle enrichment and sorting.

Colloidal particles and biological cells are patterned and separated laterally adjacent to a micropatterned electrode array by applying AC electric fields that are principally oriented normally to the electrode array. This is demonstrated for yeast cells, red blood cells, and colloidal polystyrene particles of different sizes and ζ -potentials. The separation mechanism is observed experimentally to depend on the applied field frequency and voltage. At high frequencies, particles position themselves in a manner that is consistent with dielectrophoresis, while at low frequencies, the positioning is explained in terms of a strong coupling between gravity, the vertical component of the dielectrophoretic force, and the Stokes drag on particles induced by AC electroosmotic flow. Compared to high frequency dielectrophoretic separations, the low frequency separations are faster and require lower applied voltages. Furthermore, the AC electroosmosis coupling with dielectrophoresis may enable cell separations that are not feasible based on dielectrophoresis alone. (R.D. Tilton). frequency of the applied electric field and on the conductivity of the suspending medium .

AC (Alternating Current) – Elecktrokinetics is a group of phenomena that can be used to manipulate particles and fluids in rapid and versatile ways. It is quickly becoming the center of the many biomedical chip applications [1]. These chips can be used in numerous applications such as health and food science. This project used AC – Elecktrokinetics phenomenon called DEP (Dielectrophoresis) to investigate the life cells. To elaborate, the main part of the project acquires to develop a circuitry device that was connected to an usb oscilloscope that was used for amplification among other functions. Then execute successfully dielectrophoresis on yeast cells and measure their impedances. After the electrical properties (the functions of the complex cells’ structure that can be measured electronically) such as impedances and permittivity of the cells can be observed, then the cells can be manipulated among other things that can be done on the cells by using techniques such as Electrical Impedance Spectroscopy (EIS). Furthermore, this project examined electrical characterizations of cells by applying two signals on the cells instead
of one (which was done in a previous similar project).

Myoglobin is one of the premature identifying cardiac markers, whose concentration increases from 90 pg/ml or less to over 250 ng/ml in the blood serum of human beings after minor heart attack. Separation, detection, and quantification of myoglobin play a vital role in revealing the cardiac arrest in advance, which is the challenging part of ongoing research. In the present work, one of the electrokinetic approaches, i.e., dielectrophoresis ͑DEP͒, is chosen to separate the myoglobin. A mathematical model is developed for simulating dielectrophoretic behavior of a myoglobin molecule in a microchannel to provide a theoretical basis for the above application. This model is based on the introduction of a dielectrophoretic force and a dielectric myoglobin model. A dielectric myoglobin model is developed by approximating the shape of the myoglobin molecule as sphere, oblate, and prolate spheroids. A generalized theoretical expression for the dielectrophoretic force acting on respective shapes of the molecule is derived. The microchannel considered for analysis has an array of parallel rectangular electrodes at the bottom surface. The potential and electric field distributions are calculated using Green's theorem method and finite element method. These results also compared to the Fourier series method, closed form solutions by Morgan et al. ͓J. Phys. D: Appl. Phys. 34, 1553 ͑2001͔͒ and Chang et al. ͓J. Phys. D: Appl. Phys. 36, 3073 ͑2003͔͒. It is observed that both Green's theorem based analytical solution and finite element based numerical solution for proposed model are closely matched for electric field and square electric field gradients.

Micromagnets have been reported to successfully levitate picoliter water droplets in air. Manipulation of levitating water droplets is a contamination-free alternative to digital-microfluidic labs-on-chip where droplets are handled in channels or on a substrate. An integrated electromagnetic hybrid device combining dielectrophoretic (DEP) forces to control the position of levitating droplets along a magnetic groove, is proposed. Diamagnetic forces are analytically computed with CADES while Comsol Multiphysics™ (FEM) is used for the DEP forces. Approximations of the 'point dipole model' are compared to the Maxwell Stress Tensor method applied on the 3-D model. Based on these results, an electric sequence for polarizing planar parallel Indium Tin Oxide (ITO) electrodes is proposed in order to provide a stable and accurate control of the droplet microposition along the gap. The use of these electrodes as micro-conductors to produce variable magnetic fields for magnetophoretic droplet actuation is considered and compared to DEP actuation.

We present in this paper a new Lab-on-Chip (LoC) architecture for dielectrophoresis-based cell manipulation, detection, and capacitive measurement. The proposed LoC is built around a CMOS full-custom chip and a microfluidic structure. The CMOS chip is used to deliver all parameters required to control the dielectrophoresis (DEP) features such as frequency, phase, and amplitude of signals spread on in-channel electrodes of the LoC. It is integrated to the LoC and experimental results are related to micro and nano particles manipulation and detection in a microfluidic platform. The proposed microsystem includes an on-chip 27-bit frequency divider, a digital phase controller with a 3.6 phase shift resolution and a 2.5 V dynamic range. The sensing module is composed of a 3 3 capacitive sensor array with 10 fF per mV sensitivity, and a dynamic range of 1.5 V. The obtained results show an efficient nano and micro-particles ) separation based on frequency segregation with low voltages less than 1.7 V and a fully integrated and reconfigurable system.

This article presents the numerical and experimental analysis of a dielectrophoretic-activated cell sorter (DACS), which is equipped with curved microelectrodes. Curved microelectrodes offer unique advantages, since they create strong dielectrophoretic (DEP) forces over the tips and maintain it over a large portion of their structure, as predicted by simulations. The performance of the system is assessed using yeast (Saccharomyces cerevisiae) cells as model organisms. The separation of the live and dead cells is demonstrated at different medium conductivities of 0.001 and 0.14 S/m, and the sorting performance was assessed using a second array of microelectrodes patterned downstream the microchannel. Further, microscopic cell counting analysis reveals that a single pass through the system yields a separating efficiency of ~80% at low medium conductivities and ~85% at high medium conductivities.

BackgroundThe microfabricated impedance spectroscopy flow cytometer used in this study permits rapid dielectric characterization of a cell population with a simple microfluidic channel. Impedance measurements over a wide frequency range provide information on cell size, membrane capacitance, and cytoplasm conductivity as a function of frequency. The amplitude, opacity, and phase information can be used for discrimination between different cell populations without the use of cell markers.The microfabricated impedance spectroscopy flow cytometer used in this study permits rapid dielectric characterization of a cell population with a simple microfluidic channel. Impedance measurements over a wide frequency range provide information on cell size, membrane capacitance, and cytoplasm conductivity as a function of frequency. The amplitude, opacity, and phase information can be used for discrimination between different cell populations without the use of cell markers.MethodsPolystyrene beads, red blood cells (RBCs), ghosts, and RBCs fixed in glutaraldehyde were passed through a microfabricated flow cytometer and measured individually by using two simultaneously applied discrete frequencies. The cells were characterized at 1,000 per minute in the frequency range of 350 kHz to 20 MHz.Polystyrene beads, red blood cells (RBCs), ghosts, and RBCs fixed in glutaraldehyde were passed through a microfabricated flow cytometer and measured individually by using two simultaneously applied discrete frequencies. The cells were characterized at 1,000 per minute in the frequency range of 350 kHz to 20 MHz.ResultsCell size was easily measured with submicron accuracy. Polystyrene beads and RBCs were differentiated using opacity. RBCs and ghosts were differentiated using phase information, whereas RBCs and fixed RBCs were differentiated using opacity. RBCs fixed using increasing concentrations of glutaraldehyde showed increasing opacity. This increased opacity was linked to decreased cytoplasm conductivity and decreased membrane capacitance, both resulting from protein cross-linking.Cell size was easily measured with submicron accuracy. Polystyrene beads and RBCs were differentiated using opacity. RBCs and ghosts were differentiated using phase information, whereas RBCs and fixed RBCs were differentiated using opacity. RBCs fixed using increasing concentrations of glutaraldehyde showed increasing opacity. This increased opacity was linked to decreased cytoplasm conductivity and decreased membrane capacitance, both resulting from protein cross-linking.ConclusionsThis work presents label-free differentiation of cells in an on-chip flow cytometer based on impedance spectroscopy, which will be a powerful tool for cell characterization. © 2005 Wiley-Liss, Inc.This work presents label-free differentiation of cells in an on-chip flow cytometer based on impedance spectroscopy, which will be a powerful tool for cell characterization. © 2005 Wiley-Liss, Inc.

We demonstrated the application of a simple electrode geometry for dielectrophoresis (DEP) on colloidal probes as a form of molecular force spectroscopy in a highly parallel format. The electric field between parallel plates is perturbed with dielectric microstructures, generating uniform DEP forces on colloidal probes in the range of several hundred piconewtons across a macroscopic sample area. We determined the approximate crossover frequency between negative and positive DEP using electrodes without dielectric microstructures-a simplification over standard experimental methods involving quadrupoles or optical trapping. 2D and 3D simulations of the electric field distributions validated the experimental behavior of several of our DEP tweezers geometries and provided insight into potential improvements. We applied the DEP tweezers to the stretching of a short DNA oligomer and detected its extension using total-internal reflection fluorescence microscopy. The combination of a simple cell fabrication, a uniform distribution of high axial forces, and a facile optical detection of our DEP tweezers makes this form of molecular force spectroscopy ideal for highly parallel detection of stretching or unbinding kinetics of biomolecules.

In this paper, we report a novel technological approach for three dimensional (3D) assembly of single-walled carbon nanotubes (SWNTs) using dielectrophoresis (DEP). The two terminal resistance of the assembled SWNTs is ~ 545 Ohms. Encapsulation of the 3D structure with a thin layer of parylene-C protects it from the environment and keeps it intact.

Dielectrophoresis (DEP) is the phenomenon by which polarized particles in a non-uniform electric field undergo translational motion, and can be used to direct the motion of microparticles in a surface marker-independent manner. Traditionally, DEP devices include planar metallic electrodes patterned in the sample channel. This approach can be expensive and requires a specialized cleanroom environment. Recently, a contact-free approach called contactless dielectrophoresis (cDEP) has been developed. This method utilizes the classic principle of DEP while avoiding direct contact between electrodes and sample by patterning fluidic electrodes and a sample channel from a single polydimethylsiloxane (PDMS) substrate, and has application as a rapid microfluidic strategy designed to sort and enrich microparticles. Unique to this method is that the electric field is generated via fluidic electrode channels containing a highly conductive fluid, which are separated from the sample channel by a thin insulating barrier. Because metal electrodes do not directly contact the sample, electrolysis, electrode delamination, and sample contamination are avoided. Additionally, this enables an inexpensive and simple fabrication process.

Multilayer microelectrode structures, with 10 µm feature sizes, have been fabricated using excimer laser ablation techniques. These structures will be incorporated into devices for the electro-manipulation and characterization of cells, microorganisms and other particles. The AC electrokinetic phenomena of dielectrophoresis, electrorotation and travelling electric field effects are utilized, all of which are dependent on the dielectric properties of the bioparticles. Examples are presented of a travelling wave junction and selective particle trap to be incorporated into a prototype biofactory-on-a-chip device. A technique for profiling the edges of via-holes has been developed to facilitate robust electrical connections through polyimide films in these multilayer devices.

We report a free-surface electrohydrodynamic flow phenomenon driven by an ionic wind mechanism induced by a high frequency gas-phase ac field ͑Ͼ10 kHz͒. Intense vortices Ͼ1 cm/s are generated above a critical voltage, beyond which the vortices break down to spawn off new vortex pairs leading to a cascade of vortices over a continuum of length scales; the mixing efficiency approaches a turbulent-like state. Colloidal particles are attracted and aggregated into planar crystal structures within the vortices by a combination of dielectrophoresis and shear-induced diffusion.

Janus particles are dissymmetric systems with 2 faces that could present 2 different physical/chemical properties, offering new possibilities in microfluidic research fields. This work presents a novel approach of handling the rotation of Janus particles with dielectrophoresis in a determined location at the single level. We first present the manufacturing process of those particles with fluorescent PS beads coated on one side with Au. Then spectroscopic studies investigate their optical responses under fluorescence excitation as a mean to monitor their rotation angle. Finally, Janus particles are injected in an electro-microfluidic chip exerting non-uniform localized electrical fields inside the channel. The microfluidic experiment shows that not only precise 3D localization of those particles can be achieved but moreover that their rotation can be controlled by the gradient of the applied electrical field.

We report a successful design and simulation of a novel micro-mixer with embedded micro electrodes to produce dielectrophoresis (DEP) force in order to focus particles in the middle of the channel and reduce sedimentation of particles. The device is designed to let cells with diameter of less than 15μm pass and therefore it can be integrated in the micro-scale cell sorters, which should be a key device for clinical applications. First, the concept of micro-mixers and dielectrophoresis phenomena is introduced. Then, design and simulation results of the micromixer and micro electrodes are presented, and evaluation of the mixer performance and focusing mechanism is discussed.

Dielectrophoresis, the induced motion of polarisable particles in a nonuniform electric field, has been proven as a versatile mechanism to transport, accumulate, separate and characterise micro/nano scale bioparticles in microfluidic systems. The integration of DEP systems into the microfluidics enables the inexpensive, fast, highly sensitive, highly selective and label-free detection and analysis of target bioparticles. This review provides an in-depth overview of state-of-the-art dielectrophoretic (DEP) platforms integrated into microfluidics aimed towards different biomedical applications. It classifies the current DEP systems in terms of different microelectrode configurations and operating strategies devised to generate and employ DEP forces in such processes, and compares the features of each approach. Finally, it suggests the future trends and potential applications of DEP systems in single cell analysis, stem cell research, establishing novel devices, and realising fully DEP-activated lab-on-a-chip systems.

Induced-charge electrophoresis (ICEP) has mostly been analyzed for asymmetric particles in an infinite fluid, but channel walls in real systems further break symmetry and lead to dielectrophoresis (DEP) in local field gradients. Zhao and Bau (Langmuir, 23, 2007, pp 4053) recently predicted that a metal (ideally polarizable) cylinder is repelled from an insulating wall in a DC field. We revisit this problem with an AC field and show that attraction to the wall sets in at high frequency and leads to an equilibrium distance, where DEP balances ICEP, although, in three dimensions, a metal sphere is repelled from the wall at all frequencies. This conclusion, however, does not apply to asymmetric particles. Consistent with the recent experiments of Gangwal et al. (arXiv:0708.2417), we show that a metal/insulator Janus particle is always attracted to the wall in an AC field. The Janus particle tends to move toward its insulating end, perpendicular to the field, but ICEP torque rotates this end toward the wall. Under some conditions, the theory predicts steady translation along the wall with an equilibrium tilt angle, as seen in experiments, although more detailed modeling of the contact region of overlapping double layers is required.