Dielectrophoretic Force Research Articles

Multidomain Oriented Particle Chains Based on Spatial Electric Field and Their Optical Application

The manipulation technology of particles is significant in drug screening, disease detection and treatment, etc. Here, we reported the multi-domain oriented particle chains based on spatial electric field and their optical application. According to the differences in the dielectric behavior of particles, the preparation of multi-domain oriented particle chains in the gel was successfully realized by using the dielectrophoretic force and electroosmotic rotation. This provides a new idea for manufacturing multi-structure, multi-layer, and multi-functional intelligent response materials. In addition, the factors affecting the alignment height of the particles in the gel were discussed, which was the basis for the preparation of bilayer particle chains. As an example of structural hierarchy, particle assembly has broad application prospects in optoelectronic devices and soft robots.

Quantum Dot Arrays Fabricated Using In Situ Photopolymerization of a Reactive Mesogen and Dielectrophoresis.

Dielectrophoresis (DEP) is an excellent tool for manipulating small particles within a liquid or gas medium. However, when the size of the particles is too small, such as with quantum dots (QDs), it is difficult to manipulate the particles using DEP because the dielectrophoretic force (FDEP) depends on the volume of the particles and is therefore too weak to achieve particle migration. Herein, we demonstrate a novel method for controlling nanoscale QD particles using DEP by introducing photopolymerized reactive mesogen (RM) bead vehicles. The size of an RM bead is well-controlled by the RM concentration in the medium, and when the size is approximately 0.2 μm or larger, the RM beads can be arbitrarily manipulated using DEP under moderate electric fields. Interestingly, during photopolymerization, QD particles are easily absorbed by polymerized RM beads and most of the QDs are embedded within the RM beads. Hence, we can fabricate periodic QD arrays by manipulating the RM beads containing such dots. In addition, we can fabricate multicolor QD arrays by repeating the processes using different QD particles. The shape of a DEP-assisted QD-RM network pattern can be precisely predicted by calculating the gradient of the square of the electric field (∇E2) and the corresponding FDEP. This new technology may be useful for the fabrication of optical devices, displays, photonic crystal devices, and bioapplications.

Abstract 4603: Detection of pancreatic cancer using rapid dielectrophoresis based recovery of tumor derived extra cellular vesicles and exosomes from plasma

Abstract Tumor derived extracellular vesicles, including exosomes, carry cancer related proteins on their outer surfaces making them a valuable source of tumor biomarkers in blood. However, these vesicles are difficult to recover from plasma and this prevents them from being widely used for clinical diagnostic tests. Here we present a technique that uses high conductance dielectrophoresis to rapidly recover these vesicles from plasma allowing for immunofluorescence detection of cancer related biomarkers. We demonstrate this technique can be used to detect biomarkers that successfully distinguish patients with pancreatic cancer from those with benign pancreatic disease, such as pancreatitis, as well as healthy individuals. What makes dielectrophoresis different from other vesicle recovery techniques is that it takes advantage of the large contrast in the dielectric properties between the vesicles and the surrounding plasma. The dielectrophoretic force preferentially draws vesicles to an electrode array at the bottom of a microfluidic chip where they are held in place allowing a fluidic wash to remove the bulk plasma. The vesicles are concentrated at the electrode edge thereby increasing the signal to noise ratio of the fluorescent immunostaining signal and placing the particles in known locations allowing for automated detection and quantification of biomarker levels. This technique takes 30 min to complete, requires 30-50 µl of plasma, and can be highly automated to reduce labor effort making it a promising technology for future translation into the clinical laboratory setting and enabling the use of extracellular vesicles and exosomes for diagnostic applications. Citation Format: Augusta Modestino, Jesus Bueno Alvarez, Michael Heller, Stuart Ibsen. Detection of pancreatic cancer using rapid dielectrophoresis based recovery of tumor derived extra cellular vesicles and exosomes from plasma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4603.

Triboelectric effect-modulated varifocal liquid lens

Electrically modulated varifocal liquid lenses, which are usually modulated by an external high voltage power source, have attracted much attention due to their bright application prospects in artificial optical systems. Here, a triboelectric nanogenerator (TENG)-based varifocal liquid lens (TVLL) has been demonstrated, in which the focal length can be directly modulated by external mechanical sliding. A dielectrophoretic force is generated by the TENG through the transfer of triboelectric charges in the asymmetric electrodes, which is used to continuously change the shape of the air–liquid interface between concave and convex without any complicated boost converter. Moreover, a triboelectric magnifying glass based on the accurate modulation effect of the TVLL on a light beam has been demonstrated. In this work, the TENG is used as a medium to modulate and accurately control the focal length of the liquid lens by an external mechanical stimulus, which may have great applications in micro-optical-electro-mechanical systems (MOEMS), human–machine interaction, artificial vision systems, etc.

Numerical simulation of the electric field induced in a contactless dielectrophoretic quadrupole cell separator

PurposeThis study aims to propose a contactless and continuous dielectrophoretic cell-separation device using quadrupole electric field. To examine the separation performance, numerical simulations of the electric field in the cross-section of the glass capillary installed in the center of the quadrupole electrode were conducted.Design/methodology/approachTo estimate the magnitude of the dielectrophoretic force induced on cells, electrostatic analysis was performed by using a boundary-fitted coordinate system.Distribution of the electric field and gradient of the electric field square in the cross-section of the glass capillary were simulated for various ratios of radii of the glass capillary to the electrode rod.FindingsThe distribution of the electric field was found to have a cone-like profile about the center axis of the glass capillary with maximum at the internal surface of the glass capillary. The magnitude of the gradient of electric field square had similar distribution as that of the electric field, but had steeper slope near the internal surface of the glass capillary. The optimal values of the ratio of radii and the applied voltage were also estimated to achieve the local electric field strength suitable for cell separation.Originality/valueOne major advantage of the proposed device is simple and low fabrication cost, in addition to its contactless structure free from cell damage. Derived knowledge is instructive in achieving high-throughput cell separation without the use of devices of complex structure.

Serial Separation of Microalgae in a Microfluidic Chip Under Inertial and Dielectrophoretic Forces

There are a large number and variety of microalgae in the ocean, which are important natural resources for extensive applications. However, how to identify and separate microalgae quickly and effectively remains a major challenge for investigation and utilization of microalgae resources. There are many methods for cell separation, while each of them has pros and cons. Therefore, it is difficult to meet the particular requirements of separating complex samples, such as microalgae, solely with a single method. Herein, a two-stage microfluidic separation chip was designed by combining inertial and dielectrophoretic (DEP) forces, which can achieve rapid and accurate separation of three common microalgae cells, including Platymonas , Closterium and Chlorella , with separation efficiency exceeding 90%. In the first-stage, high-throughput inertial separation technique was used to separate microalgae with their different equilibrium positions. Then, the DEP force was used to separate microalgae cells which were not separated in the first-stage through their dielectric properties. To the best of our knowledge, there is no prior reports of microalgae separation by combining DEP and inertial techniques. In addition, the DEP characteristics of microalgae cells under a non-uniform AC electric field were firstly reported in this study, and the DEP responses of each cell type were measured against AC electrical frequency changes. These findings may contribute to our understanding of the dielectric properties of microalgae, as well as the development of novel techniques for microalgae separation, detection, and marine environmental monitor and analysis.

Guided Electrokinetic Assembly of Polystyrene Microbeads onto Photopatterned Carbon Electrode Arrays

Assembly of microdevices from constituent parts currently relies on slow serial steps via direct assembly processes such as pick-and-place operations. Template Electrokinetic Assembly (TEA), a guided, noncontact assembly process, is presented in this work as a promising alternative to serial assembly processes. To characterize the process and its implementation of electrokinetic, dielectrophoretic, and electro-osmotic phenomena, we conducted studies to examine the assembly of polymer microparticles at specific locations on glassy carbon interdigitated electrode arrays (IDEAs). The IDEAs are coated with a layer of lithographically patterned resist, so that when an AC electric field is applied to the IDEA, microparticles suspended in the aqueous solution are attracted to the open regions of the electrodes not covered by photoresist. Interplay between AC electro-osmosis and dielectrophoretic forces guides 1 and 5 μm diameter polystyrene beads to assemble in regions, or "wells", uncovered by photoresist atop the electrodes. It was discovered that AC electro-osmosis under an applied frequency of 1 kHz is sufficient to effectively agglomerate 1 μm beads in the wells, whereas a stepwise process involving the application of a 1 MHz signal, followed by a 1 kHz signal, is required for the positioning of 5 μm beads, which are mainly affected by dielectrophoretic forces. Permanent entrapment of the microparticles is then demonstrated via the electropolymerization process of the conducting polymer polypyrrole.

Using a Dielectrophoretic Microfluidic Biochip Enhanced Fertilization of Mouse Embryo in Vitro.

Droplet microfluidics has appealed to many interests for its capability to epitomize cells in a microscale environment and it is also a forceful technique for high-throughput single-cell epitomization. A dielectrophoretic microfluidic system imitates the oviduct of mammals with a microchannel to achieve fertilization in vitro (IVF) of an imprinting control-region (ICR) mouse. We applied a microfluidic chip and a positive dielectrophoretic (p-DEP) force to capture and to screen the sperm for the purpose of manipulating the oocyte. The p-DEP responses of the oocyte and sperm were exhibited under applied bias conditions (waveform AC 10 Vpp, 1 MHz) for trapping 1 min. The insemination concentration of sperm nearby the oocyte was increased to enhance the probability of natural fertilization through the p-DEP force trapping. A simulation tool (CFDRC-ACE+) was used to simulate and to analyze the distribution of the electric field. The DEP microfluidic devices were fabricated using poly (dimethylsiloxane) (PDMS) and ITO (indium tin oxide)-glass with electrodes. We discuss the requirement of sperm in a DEP microfluidic chip at varied concentrations to enhance the future rate of fertilization in vitro for an oligozoospermia patient. The result indicates that the rate of fertility in our device is 17.2 ± 7.5% (n = 30) at about 3000 sperms, compatible with traditional droplet-based IVF, which is 14.2 ± 7.5% (n = 28).

A four-way coupled CFD-DEM modeling framework for charged particles under electrical field with applications to gas insulated switchgears

Particulate flows with charged particles under electric flow field exist in many practical applications, including metal particles in Gas Insulated Switchgear (GIS) or manipulation of powders in fluidized bed. The motions of these particles are affected by the electrical field, ambient flow and collisions. This work further develops the four-way coupled CFD-DEM framework under electric field, which not only computes the coupling of flow field, electric field with particle motion and particle charge, the particle-occupied solid fractions on CFD cell, particle-particle interactions and particle-wall interactions, but also considers the dielectrophoretic force, particle-particle Coulomb force, virtual mass force and Magnus force. Particle electrification on its contact with electrode is computed as well. Besides, the multi-sphere model is also introduced into the present framework in order to simulate particles of irregular shapes. The model is validated with theoretic solutions and experiments, and is applied to GIS and fluidized bed. Based on the framework, statistic information from the particulate flow in GIS, e.g., time-averaged solid fraction, time-averaged electric field or particles' velocity and charge distribution are analyzed. A dimensionless number is proposed to predict the particle motion in GIS with Alternating Current (AC), which is further conducive to reducing the parameter window in relevant simulations and studies.

Railing Nanoparticles Along Activated Tracks Towards Continuous-Flow Electrokinetic Enrichment from Blood Plasma.

We report on a unique microfluidic device that can enrich nanoparticles in a continuous flow by railing them along activated tracks (electrodes). This was achieved based on dielectrophoretic force and electrohydrodynamic drag (electrothermal rolls and AC electroosmosis) in both low and high conductive media. The results have implication for the isolation of high quality and pure nanoparticles such as exosomes from biofluids for applications in cancer diagnosis and prognosis.

Dielectrophoretic Microfluidic Device for Separating Microparticles Based on Size with Sub-Micron Resolution.

This article details the mathematical model of a microfluidic device aimed at separating any binary heterogeneous sample of microparticles into two homogeneous samples based on size with sub-micron resolution. The device consists of two sections, where the upstream section is dedicated to focusing of microparticles, while the downstream section is dedicated to separation of the focused stream of microparticles into two samples based on size. Each section has multiple planar electrodes of finite size protruding into the microchannel from the top and bottom of each sidewall; each top electrode aligns with a bottom electrode and they form a pair leading to multiple pairs of electrodes on each side. The focusing section subjects all microparticles to repulsive dielectrophoretic force, from each set of the electrodes, to focus them next to one of the sidewalls. This separation section pushes the big microparticles toward the interior, away from the wall, of the microchannel using repulsive dielectrophoretic force, while the small microparticles move unaffected to achieve the desired degree of separation. The operating frequency of the set of electrodes in the separation section is maintained equal to the cross-over frequency of the small microparticles. The working of the device is demonstrated by separating a heterogeneous mixture consisting of polystyrene microparticles of different size (radii of 2 and 2.25 μm) into two homogeneous samples. The mathematical model is used for parametric study, and the performance is quantified in terms of separation efficiency and separation purity; the parameters considered include applied electric voltages, electrode dimensions, outlet widths, number of electrodes, and volumetric flowrate. The separation efficiencies and separation purities for both microparticles are 100% for low volumetric flow rates, a large number of electrode pairs, large electrode dimensions, and high differences between voltages in both sections.

Applications of Converged Various Forces for Detection of Biomolecules and Novelty of Dielectrophoretic Force in the Applications.

Since separation of target biomolecules is a crucial step for highly sensitive and selective detection of biomolecules, hence, various technologies have been applied to separate biomolecules, such as deoxyribonucleic acid (DNA), protein, exosome, virus, etc. Among the various technologies, dielectrophoresis (DEP) has the significant advantage that the force can provide two different types of forces, attractive and repulsive DEP force, through simple adjustment in frequency or structure of microfluidic chips. Therefore, in this review, we focused on separation technologies based on DEP force and classified various separation technologies. First, the importance of biomolecules, general separation methods and various forces including DEP, electrophoresis (EP), electrothermal flow (ETF), electroosmosis (EO), magnetophoresis, acoustophoresis (ACP), hydrodynamic, etc., was described. Then, separating technologies applying only a single DEP force and dual force, moreover, applying other forces simultaneously with DEP force were categorized. In addition, advanced technologies applying more than two different kinds of forces, namely complex force, were introduced. Overall, we critically reviewed the state-of-the-art of converged various forces for detection of biomolecules with novelty of DEP.

Precise capture and dynamic relocation of nanoparticulate biomolecules through dielectrophoretic enhancement by vertical nanogap architectures

Toward the development of surface-sensitive analytical techniques for biosensors and diagnostic biochip assays, a local integration of low-concentration target materials into the sensing region of interest is essential to improve the sensitivity and reliability of the devices. As a result, the dynamic process of sorting and accurate positioning the nanoparticulate biomolecules within pre-defined micro/nanostructures is critical, however, it remains a huge hurdle for the realization of practical surface-sensitive biosensors and biochips. A scalable, massive, and non-destructive trapping methodology based on dielectrophoretic forces is highly demanded for assembling nanoparticles and biosensing tools. Herein, we propose a vertical nanogap architecture with an electrode-insulator-electrode stack structure, facilitating the generation of strong dielectrophoretic forces at low voltages, to precisely capture and spatiotemporally manipulate nanoparticles and molecular assemblies, including lipid vesicles and amyloid-beta protofibrils/oligomers. Our vertical nanogap platform, allowing low-voltage nanoparticle captures on optical metasurface designs, provides new opportunities for constructing advanced surface-sensitive optoelectronic sensors.

Force on Dielectric by the Fringe Field: Comparison to Dielectrophoretic Force

In this manuscript, the force exerted on the dielectric in the fringe field from the two conducting parallel plates with applied electrical potential was calculated and found to be an effective micro/nanoscale manipulation tool. The conformal mapping was employed to obtain the fringe field generated from the edges of the plates. The strong gradient of the fringe field near the edges was manifested in both parametric mapping and simulation. It was found that the force analytically obtained from the fringe field was proportional and directed to the gradient of the squared electric field. The result was compared to dielectrophoresis (DEP).

Sequentially addressable dielectrophoretic array for high-throughput sorting of large-volume biological compartments.

Droplet microfluidics has become a powerful tool in precision medicine, green biotechnology, and cell therapy for single-cell analysis and selection by virtue of its ability to effectively confine cells. However, there remains a fundamental trade-off between droplet volume and sorting throughput, limiting the advantages of droplet microfluidics to small droplets (<10 pl) that are incompatible with long-term maintenance and growth of most cells. We present a sequentially addressable dielectrophoretic array (SADA) sorter to overcome this problem. The SADA sorter uses an on-chip array of electrodes activated and deactivated in a sequence synchronized to the speed and position of a passing target droplet to deliver an accumulated dielectrophoretic force and gently pull it in the direction of sorting in a high-speed flow. We use it to demonstrate large-droplet sorting with ~20-fold higher throughputs than conventional techniques and apply it to long-term single-cell analysis of Saccharomyces cerevisiae based on their growth rate.

Bridging and discharge mechanisms of cellulose impurities in transformer oil under DC voltage

Cellulose impurities seriously threaten the insulating performance of oil-pressboard insulation. In this paper, we investigate the bridging and discharge mechanisms of cellulose impurities in transformer oil under DC voltage. The results show that under the non-uniform DC electric field, the cellulose impurities are mainly subjected to forces including gravity, buoyancy, dielectrophoretic force and drag force, among which the dielectrophoretic force dominates the bridging of the impurities. By studying the leakage current of dry (moisture 8 ppm) and wet (moisture 26 ppm) oil samples with and without cellulose bridges, deductions are made that the coexistence of cellulose and water in oil leads to the formation of a cellulose-water bridge, which increases the leakage current within the oil, causing a heating effect and gasifying the water on the bridge. Further analysis indicates that when the amount of gasified water exceeds the permeation channel threshold, the cellulose-water bridge transforms into a cellulose-gas bridge. Final oil breakdown happens along this gaseous bridge.

Dielectrophoretic Immobilization of Yeast Cells Using CMOS Integrated Microfluidics.

This paper presents a dielectrophoretic system for the immobilization and separation of live and dead cells. Dielectrophoresis (DEP) is a promising and efficient investigation technique for the development of novel lab-on-a-chip devices, which characterizes cells or particles based on their intrinsic and physical properties. Using this method, specific cells can be isolated from their medium carrier or the mixture of cell suspensions (e.g., separation of viable cells from non-viable cells). Main advantages of this method, which makes it favorable for disease (blood) analysis and diagnostic applications are, the preservation of the cell properties during measurements, label-free cell identification, and low set up cost. In this study, we validated the capability of complementary metal-oxide-semiconductor (CMOS) integrated microfluidic devices for the manipulation and characterization of live and dead yeast cells using dielectrophoretic forces. This approach successfully trapped live yeast cells and purified them from dead cells. Numerical simulations based on a two-layer model for yeast cells flowing in the channel were used to predict the trajectories of the cells with respect to their dielectric properties, varying excitation voltage, and frequency.

In situ electric field driven assembly to construct adaptive graded permittivity BaTiO3/epoxy resin composites for improved insulation performance

The applications of dielectric functionally graded materials in high-voltage systems have emerged as a potential strategy to obtain superior insulation performance in recent years. However, the existing preparation methods mainly rely on simple lamination or centrifugal force intervention, and cannot adapt to the complex electric field spatial distribution. In this work, we developed low partial discharge (PD), high flashover voltage barium titanate/epoxy resin (BT/ER) insulation composites with graded permittivity, which were assembled by the in situ electric field. Our approach involves (a) the migration and deposition of BT in high electric field strength regions, driven by in situ electrophoretic forces in the BT/ER suspension (dispensable), (b) the alignment of BT in high electric field strength regions, driven by in situ dielectrophoretic forces in the BT/ER suspension, and (c) the “freezing” of the composite structure by curing. The insulation performance of the samples after this electric field structuring was assessed by PD measurements and flashover tests. The PD of the samples with 2.0 vol% BT and electric field treatment was significantly reduced, and the flashover voltage was increased by 31.8% compared with the pure ER sample. Optical microscope images, scanning electron microscope (SEM) images and finite element simulations also verify that this type of electric field structuring can effectively reduce the electric field non-uniform coefficient. We believe that the strategy of electric field assembly to prepare graded permittivity materials (GPMs) is promising candidate for high performance insulation applications.

Response properties of nitrogen dioxide gas sensors with tin oxide decorated carbon nanotube channel fabricated by two-step dielectrophoretic assembly

Gas sensors with carbon nanotubes (CNTs) and tin dioxide (SnO2) nanoparticles for nitrogen dioxide (NO2) detection are fabricated using a two-step dielectrophoretic (DEP) assembly method, and the NO2 gas detection properties are investigated. For the fabrication of the sensor, CNTs assemble between electrodes by a DEP force, followed by SnO2 nanoparticle decoration also by a DEP assembly method, and the assembled CNTs act as high electric field electrodes. The formed CNT/SnO2 gas sensors exhibit a sharp increase in resistance followed by a gradual decrease upon NO2 exposure. pn hetero-junctions are formed between the CNTs and the SnO2 nanoparticles, and the resistance shift of the depletion region in the CNTs at the pn hetero-junction induces the sharp increase in the resistance.

Smartphone enabled medical diagnostics by optically tracking electromagnetically induced harmonic oscillations of magnetic particles suspended in analytes

Smartphone based point of care (POCT) medical diagnostic technology could potentially facilitate healthcare to remote locations with limited medical infrastrucure. However, such protocols exhibit background noise due to non-specific interactions as well as requiring long measurement times that limit their applications. We propose a procedure based on magnetic particle (MPs) that combines three dimensional electromagnetically induced oscillation of MPs with high precision optical tracking of the MPs. The measurement consisted of dropping MPs functionalized with streptavidin onto gold thin film actuators fabricated on silicon nitride substrates. Sinusoidal currents were passed through the actuators to move the MPs by horizontal dielectrophoretic forces. Simultaneously, a vertical magnetic field was applied to promote interaction between the MPs with biotin functionalized onto the substrates. The surfaces of MPs were functionalized with competing biotin whose concentration was varied. A high-resolution (4 K) video of the sensing surface was recorded with a smartphone and simultaneous tracking of 8000–10,000 MPs allowed us to identify MPs that interacted specifically with probes on the surface and ceased to show harmonic oscillations. Importantly, the dielectrophoretic forces reduced non-specific interactions and enhanced the probability of specific interactions while vertical magnetic forces accelerated the interaction of MPs with the functionalized surface. Our approach enabled a detection limit of 1 nM for biotin with a dynamic range of four orders of magnitude with a measurement time of approximately 2 min and video analysis time of 7 min. These results show that combining MPs and dynamic particle tracking is a promising method for practical POCT.