Positive Dielectrophoresis Force Research Articles

Designing a new microchannel to collect microparticles using dielectrophoretic forces: Numerical and experimental investigation

Dielectrophoresis (DEP) is an effective technique for manipulating particles in microfluidic devices. The DEP force depends on the frequency and square gradient of the electric field, as well as the fluid and particle dielectric properties. An efficient system for manipulating particles can be designed by adjusting these factors. This study aims to develop an efficient microsystem for particle trapping using dual-frequency DEP force. The microfluidic system is divided into two parts of focusing and attracting. The negative DEP (nDEP) force in the focusing part concentrates particles near the microchannel axis. The positive DEP (pDEP) force in the attractive area then absorbs particles into the internal chamber via electrodes. In general, the main advantage of the present design is the maximum trapping of incoming particles (with a trapping rate of over 95%) regardless of their initial location. In this study, numerical modeling was first done in three dimensions to sort and trap the microparticles. Then, a microchip was designed, built, and tested in a laboratory to validate the results and confirm the microfluidic system behavior. Finally, a parametric study was conducted to figure out the best voltage range of the electric fields in the microfluidic system.

A dielectrophoresis-based platform of cancerous cells capture using aptamer-functionalized gold nanoparticles in a microfluidic channel.

In this paper, a microfluidic chip for the manipulation and capture of cancer cells was introduce. In which, the combination of dielectrophoresis (DEP) and a binding method based on chemical interactions by using cell-specific aptamer was performed to enhance the capture strength and specificity. The device has been simply constructed from a straight-channel PDMS placed on a glass substrate that patterned electrode structures and a self-assembled monolayer (SAM) of gold nanoparticles (AuNPs). The target cells were transported to the manipulation area by flow and attracted down to the region between the electrodes under the influence of positive dielectrophoresis force (pDEP). This approach facilitated subsequent selective capture by the modified aptamers on the AuNPs. The distribution of the electric field in the channel has also been simulated to clarify the DEP operation. As a result, the device has been shown to effectively capture target lung cancer cells with a concentration as low as cells/mL. The capture specificity in a sample of mixed cells is up to 80.4%. This technique has the potential to be applied to detection methods for many types of cancer. This article is protected by copyright. All rights reserved.

New Generation Dielectrophoretic-Based Microfluidic Device for Multi-Type Cell Separation

This study introduces a new generation of dielectrophoretic-based microfluidic device for the precise separation of multiple particle/cell types. The device features two sets of 3D electrodes, namely cylindrical and sidewall electrodes. The main channel of the device terminates with three outlets: one in the middle for particles that sense negative dielectrophoresis force and two others at the right and left sides for particles that sense positive dielectrophoresis force. To evaluate the device performance, we used red blood cells (RBCs), T-cells, U937-MC cells, and Clostridium difficile bacteria as our test subjects. Our results demonstrate that the proposed microfluidic device could accurately separate bioparticles in two steps, with sidewall electrodes of 200 µm proving optimal for efficient separation. Applying different voltages for each separation step, we found that the device performed most effectively at 6 Vp-p applied to the 3D electrodes, and at 20 Vp-p and 11 Vp-p applied to the sidewall electrodes for separating RBCs from bacteria and T-cells from U937-MC cells, respectively. Notably, the device's maximum electric fields remained below the cell electroporation threshold, and we achieved a separation efficiency of 95.5% for multi-type particle separation. Our findings proved the device's capacity for separating multiple particle types with high accuracy, without limitation for particle variety.

A microfluidic chip integrated with 3D sidewall electrodes and wavy microchannel for cell focusing and separation

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

Bacteria and cancer cell pearl chain under dielectrophoresis.

In this work, we aim to observe and study the physics of bacteria and cancer cells pearl chain formation under dielectrophoresis (DEP). Experimentally, we visualized the formation of Bacillus subtilis bacterial pearl chain and human breast cancer cell (MCF-7) chain under positive and negative dielectrophoretic force, respectively. Through a simple simulation with creeping flow, AC/DC electric fields, and particle tracing modules in COMSOL, we examined the mechanism by which bacteria self-organize into a pearl chain across the gap between two electrodes via DEP. Our simulation results reveal that the region of greatest positive DEP force shifts from the electrode edge to the leading edge of the pearl chain, thus guiding the trajectories of free-flowing particles toward the leading edge via positive DEP. Our findings additionally highlight the mechanism why the free-flowing particles are more likely to join the existing pearl chain rather than starting a new pearl chain. This phenomenon is primarily due to the increase in magnitude of electric field gradient, and hence DEP force exerted, with the shortening gap between the pearl chain leading edge and the adjacent electrode. The findings shed light on the observed behavior of preferential pearl chain formation across electrode gaps.

A novel automatic segmentation and tracking method to measure cellular dielectrophoretic mobility from individual cell trajectories for high throughput assay

Background and ObjectiveThe dielectrophoresis (DEP) technique is increasingly being recognised as a potentially valuable tool for non-contact manipulation of numerous cells as well as for biological single cell analysis with non-invasive characterisation of a cell's electrical properties. Several studies have attempted to track multiple cells to characterise their cellular DEP mobility. However, they encountered difficulties in simultaneously tracking the movement of a large number of individual cells in a bright-field image sequence because of interference from the background electrode pattern. Consequently, this present study aims to develop an automatic system for imaging-based characterisation of cellular DEP mobility, which enables the simultaneous tracking of several hundred of cells inside a microfluidic device. Methods: The proposed method for segmentation and tracking of cells consists of two main stages: pre-processing and particle centre localisation. In the pre-processing stage, background subtraction and contrast enhancement were performed to distinguish the cell region from the background image. In the particle centre localisation stage, the unmarked cell was automatically detected via graph-cut algorithm-based K-means clustering. Results: Our algorithm enabled segmentation and tracking of numerous Michigan Cancer Foundation-7 (MCF-7) cell trajectories while the DEP force was oscillated between positive and negative. The cell tracking accuracy and cell count capability was at least 90% of the total number of cells with the newly developed algorithm. In addition, the cross-over frequency was measured by analysing the segmented and tracked trajectory data of the cellular movements caused by the positive and negative DEP force. The measured cross-over frequency was compared with previous results. The multi-cellular movements investigation based on the measured cross-over frequency was repeated until the viability of cells was unchanged in the same environment as in a microfluidic device. The results were statistically consistent, indicating that the developed algorithm was reliable for the investigation of DEP cellular mobility. Conclusion: This study developed a powerful platform to simultaneously measure the DEP-induced trajectories of numerous cells, and to investigate in a robust, efficient, and accurate manner the DEP properties at both the single cell and cell ensemble level.

Sequential Cell-Processing System by Integrating Hydrodynamic Purification and Dielectrophoretic Trapping for Analyses of Suspended Cancer Cells.

Microfluidic devices employing dielectrophoresis (DEP) have been widely studied and applied in the manipulation and analysis of single cells. However, several pre-processing steps, such as the preparation of purified target samples and buffer exchanges, are necessary to utilize DEP forces for suspended cell samples. In this paper, a sequential cell-processing device, which is composed of pre-processing modules that employ deterministic lateral displacement (DLD) and a single-cell trapping device employing an electroactive microwell array (EMA), is proposed to perform the medium exchange followed by arraying single cells sequentially using DEP. Two original microfluidic devices were efficiently integrated by using the interconnecting substrate containing rubber gaskets that tightly connect the inlet and outlet of each device. Prostate cancer cells (PC3) suspended in phosphate-buffered saline buffer mixed with microbeads were separated and then resuspended into the DEP buffer in the integrated system. Thereafter, purified PC3 cells were trapped in a microwell array by using the positive DEP force. The achieved separation and trapping efficiencies exceeded 94% and 93%, respectively, when using the integrated processing system. This study demonstrates an integrated microfluidic device by processing suspended cell samples, without the requirement of complex preparation steps.

Measuring Dielectrophoresis Force for Metallic and Non-metallic Particle Manipulations via a Quartz Tuning Fork Atomic Force Microscope

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

Numerical study of insulation structure characteristics and arrangement effects on cell trapping using alternative current insulating based dielectrophoresis

Insulator-based dielectrophoresis is a recently developed technique in which insulating posts are used to produce non-uniformity in the electric field in a microchannel. This study presents the effects of insulating posts geometry and arrangement on the trapping efficiency of red blood cells in an alternating current- Insulator-based dielectrophoresis system. Microchannels containing square, circular and diamond-shaped posts with particles under the influence of positive dielectrophoresis force and fluid flow were considered. Finite element method was used to compute the velocity of the flow and electric field. The numerical method was verified by comparing the numerical results with experimental data. Two distinct criteria for examining particle trapping for distinct shapes and arrangements of insulating posts were introduced. Particle tracing simulation was implemented to observe particle trapping and compare the trapping performance of systems with distinct posts. As shown in the results for the system with circular and square posts, insulators should be narrowed to improve particle trapping, while diamond post should be widened to increase the trapping efficiency. In addition, the particle tracing results showed that microchannel with square posts is more efficient in particle trapping.

Combining 3D sidewall electrodes and contraction/expansion microstructures in microchip promotes isolation of cancer cells from red blood cells

Cell sorting from heterogeneous organisms and tissues composed of multi-type cells is of great importance in biological and clinical applications. As promising cell sorting methods, dielectrophoresis (DEP) and hydrodynamics are attracting much attention in recent years. In this paper, we report a novel strategy by coupling DEP unit (3D sidewall electrodes) and hydrodynamic unit (microchannels with contraction/expansion structures) together in one microfluidic chip. Depending on the relative positions of 3D sidewall electrodes and contraction/expansion structure, three microchips (full-coupling, semi-coupling and non-coupling) are developed and their cell sorting performance are compared by isolating lung cancer cells (PC-9 cells) from red blood cells (RBCs). Both finite element simulation and practical cell sorting prove that high cell sorting efficiency (recovery of PC-9 cells: 90.21%, recovery of RBCs: 94.35%) can be achieved in full-coupling microchip, mainly owing to the synergistic effects between DEP sorting and hydrodynamic sorting. i.e., the positive DEP force generated by 3D sidewall electrodes can simultaneously act as an additional shear gradient lift force and thus trigger secondary flow even at low flow velocity. Live/dead cell staining, hemolysis ratio, fluorescence images and CCK-8 assay prove that RBCs and PC-9 cells show no significance difference in cell viability before and after cell sorting. The proposed coupling platform for cell sorting brings on a new pathway to construct integrated microfluidic chips for effective cell sorting and separation.

Low concentration E. coli O157:H7 bacteria sensing using microfluidic MEMS biosensor.

This paper reports the design, fabrication, and testing of a microfluidic MEMS biosensor for rapid sensing of low concentration Escherichia coli O157:H7. It consists of a specially designed focusing and sensing region, which enables the biosensor to detect low concentration of bacterial cells. The focusing region consists of a ramped vertical electrode pair made of electroplated gold along with tilted thin film finger pairs (45°) embedded inside a microchannel. The focusing region generates positive dielectrophoresis force, which moves the cells towards the edges of the tilted thin film electrode fingers, located at the center of the microchannel. The fluidic drag force then carries the focused cells to the sensing region, where three interdigitated electrode arrays (IDEAs) with 30, 20, and 10 pairs, respectively, are embedded inside the microchannel. This technique resulted in highly concentrated samples in the sensing region. The sensing IDEAs are functionalized with the anti-E. coli antibody for specific sensing of E. coli 0157:H7. As E. coli binds to the antibody, it results in an impedance change, which is measured across a wide frequency range of 100 Hz-10 MHz. The biosensor was fabricated on a glass substrate using the SU8 epoxy resist to form the microchannel, gold electroplating to form the vertical focusing electrode pair, a thin gold film to form the sensing electrode, the finger electrodes, traces and bonding pads, and polydimethylsiloxane to seal the device. The microfluidic impedance biosensor was tested with various low concentration bacterial samples and was able to detect bacterial concentration, as low as 39 CFU/ml with a total sensing time of 2 h.

An impedance biosensor for simultaneous detection of low concentration of Salmonella serogroups in poultry and fresh produce samples

This paper reports the design, fabrication and testing of a microfluidic based impedance biosensor for rapid and simultaneous detection of three Salmonella serogroups. The microfluidic device consists of three microchannels, each one includes a region for focusing the Salmonella cells into the centerline of the microchannel and direct them toward the sensing region to obtain highly concentrated samples using positive dielectrophoresis force. A region for bacteria sensing consists of interdigitated electrode (IDE) array with 10 pairs of fingers. Three types of Salmonella antibodies (type B, D and E) were mixed separately with the cross-linker (Sulfo-LC-SPDP) to enhance the immobalization of the antibodies to the detection electrodes. The electrode surfaces was then functionalized with the three mixtures, one for each channel. As target antigen binds to the antibody, it results in impedance change. The Salmonella samples were spiked with Salmonella type B, introduced into the biosensor via the sample inlet into the focusing region, and then toward the sensing region where they bind to the immobilized antibody, causing a change in the impedance. The performance of the devices was tested using single Salmonella serotype B and two Salmonella serotypes B, and D, with a limit of detection of 7 cells/ml. The biosensor was also able to differentiate live from dead bacteria eliminating the false positive results. Finally, the device was also able to detect Salmonella selectively when other type of pathogen was present.

Dielectrophoretic separation of microalgae cells in ballast water in a microfluidic chip.

The composition of the ship's ballast water is complex and contains a large number of microalgae cells, bacteria, microplastics, and other microparticles. To increase the accuracy and efficiency of detection of the microalgae cells in ballast water, a new microfluidic chip for continuous separation of microalgae cells based on alternating current dielectrophoresis was proposed. In this microfluidic chip, one piece of 3-dimensional electrode is embedded on one side and eight discrete electrodes are arranged on the other side of the microchannel. An insulated triangular structure between electrodes is designed for increasing the inhomogeneity of the electric field distribution and enhancing the dielectrophoresis (DEP) force. A sheath flow is designed to focus the microparticles near the electrode, so as to increase the suffered DEP force and improve separation efficiency. To demonstrate the performance of the microfluidic separation chip, we developed two species of microalgae cells (Platymonas and Closterium) and a kind of microplastics to be used as test samples. Analyses of the related parameters and separation experiments by our designed microfluidic chip were then conducted. The results show that the presented method can separate the microalgae cells from the mixture efficiently, and this is the first time to separate two or more species of microalgae cells in a microfluidic chip by using negative and positive DEP force simultaneously, and moreover it has some advantages including simple operation, high efficiency, low cost, and small size and has great potential in on-site pretreatment of ballast water.

3D Carbon-Electrode Dielectrophoresis for Enrichment of a Small Cell Population from a Large Sample Volume

Isolation and enrichment of cells from a diluted sample is necessary for different clinical applications. Here we have demonstrated the use of 3D carbon electrode dielectrophoresis (DEP) to process a diluted yeast sample featuring concentration as low as 102 cells/ml. The yeast cells in the sample were first trapped on carbon electrodes by implementing positive DEP force and then released and concentrated in a small volume of clean buffer. The maximum limit of the cell trapping for our device was found to be around 4000 cells. Using 10 µl/min, an enrichment of 154.2 ± 23.7 folds was achieved, where sample of 102 cells/ml concentration was enriched up to 4 X 104 cells/ml. Upon increasing the flow rate up to 30 µl/min, the enrichment dropped down to 18.4 ± 4 folds due to the increase of drag force, though the enriched concentration around 104 cells/ml was still achieved.

Label-free detection of multidrug resistance in K562 cells through isolated 3D-electrode dielectrophoresis.

Dielectrophoresis (DEP), a technique used to separate particles based on different sizes and/or dielectric properties under nonuniform electric field, is a promising method to be applied in label-free, rapid, and effective cell manipulation and separation. In this study, a microelectromechanical systems-based, isolated 3D-electrode DEP device has been designed and implemented for the label-free detection of multidrug resistance in K562 leukemia cells, based on the differences in their cytoplasmic conductivities. Cells were hydrodynamically focused to the 3D-electrode arrays, placed on the side walls of the microchannel, through V-shaped parylene-C obstacles. 3D-electrodes extruded along the z-direction provide uniformly distributed DEP force through channel depth. Cell suspension containing resistant and sensitive cancer cells with 1:100 ratio was continuously flown through the channel at a rate of 10 μL/min. Detection was realized at 48.64 MHz, the cross-over frequency of sensitive K562 cells, at which sensitive cells flow with the fluid, while the resistant ones are trapped by positive DEP force. Device can be operated at considerably low voltages (<9 Vpp ). This is achieved by means of a very thin (0.5 μm) parylene coating on electrodes, providing the advantages offered by the isolation of electrodes from the sample, while the working voltage can still be kept low. Results prove that the presented DEP device can provide an efficient platform for the detection of multidrug resistance in leukemia, in a label-free manner.

Multistep manipulations of poly(methyl-methacrylate) submicron particles using dielectrophoresis

A microfluidic chip for multi-step manipulations of polymethylmethacrylate submicron particles (PMMA-SMPs) based on dielectrophoresis (DEP) has been developed that includes four main functions of focusing, guiding, trapping and releasing the submicron particles. The structure of the DEP chip consists of a top electrode made of indium tin oxide (ITO), a flow chamber formed by optically clear adhesive (OCA) tape and bottom electrodes with different patterns for different purposes. The bottom electrodes can be divided into three parts: a fish-bone type electrode array which provides the positive DEP force for focusing the suspended nanoparticles near the inlet in the flow chamber; the second is for switching and guiding the focused nanoparticles along the electrode surface to the target area, like a flow passing along a virtual channel; and a trapping electrode in the downstream for trapping and releasing the guided nanoparticles. According to the simulation and experimental results, nanoparticles can be aligned along the electrode of the focusing electrode and guided toward the target electrode by means of a positive DEP force between the top and bottom electrodes, with the effects of Brownian motion and Stokes force. In order to demonstrate the sequence of DEP manipulations, a PMMA-NP suspension is introduced to the DEP chip; the size of the PMMA-SMPs is about 300 nm. Furthermore, a LabVIEW program developed for sequence control of the AC signals for the multi-step manipulations. Consequently, the DEP chip provides an excellent platform technology for the multi-step manipulation of submicron particles.

Creation of single-particle environment by positive dielectrophoresis and liquid dielectrophoresis

Two electrical mechanisms for manipulating particles and fluids, dielectrophoresis (DEP) and liquid dielectrophoresis (LDEP), are integrated in a microfluidic chip for creating the single-particle environment. The fluid is activated by LDEP with a 100-kHz/240-Vpp signal. When the single polystyrene bead approaches the trapping area, positive DEP force is utilized to capture and immobilize the bead. After trapping the bead, the process of liquid cutting and droplet creation is employed to create a droplet containing a single bead by LDEP with a 100-kHz/320-Vpp signal.

Controlling SWCNT assembling density by electrokinetics

Single-walled carbon nanotubes (SWCNTs) as the colloid in a colloidal solution can be polarized in a non-uniform electric field and experience a net force that is the so-called dielectrophoresis (DEP) force, due to the interaction between the induced dipoles and the electric field. The positive DEP force can be used to position and assemble arrays of SWCNTs. Inversely, the negative DEP force can be utilized to separate SWCNTs in terms of their electronic properties. Moreover, Joule heating generated by the electric field can lead to other electrokinetics forces in the colloidal solution, which give rise to fluidic motion of the solution. Additionally, at low frequencies, the electrical double layer also induces a steady fluidic motion, a phenomenon known as AC electroosmotic flow. These fluidic motion in turn exerts a drag force on the nanotubes. Hence, to controllably assemble SWCNTs using DEP force is a non-trivial task. In this article, the mechanisms of electrokinetics and electrohydrodynamics are systematically analyzed through numerical simulations for a set of parameters that are typically used for assembling SWCNTs between metal electrodes. Finally, experimental results from the frequency-dependent assembly of SWCNTs using this set of parameters are described and discussed. These results show that the density of SWCNTs assembled between electrodes can be varied by controlling the electrokinetics parameters.

Dielectrophoretic chip with multilayer electrodes and micro-cavity array for trapping and programmably releasing single cells

Cell characterization analysis usually involves a sequence of steps such as culture, separation, trapping, examination and recollection. In general, it is difficult to recover the identified cells and achieve a multi-run examination on a single chip for clinical samples. In the present study, a dielectrophoresis (DEP) micro-device was developed for multi-step manipulations of cells at the single-cell level. The structure of the DEP chip consisted of an indium tin oxide (ITO) top electrode, a flow chamber, a middle electrode on an SU-8 surface, a micro-cavity array of SU-8 and distributed electrodes at the bottom of the micro-cavities. The purpose of the three-layer-electrode design was threefold. First, cells could be trapped into the micro-cavities by negative DEP between the top and middle electrodes. After cells were trapped, cell analysis at the single-cell level could potentially be performed. This could include, for example, drug treatment or biomedical sensing on the chip without applying voltage. Once identified, the target cells could be individually released by controlling the bottom distributed electrodes. Finally, the rest of the trapped cells could be pulled out by a positive DEP force between the top and middle electrodes and flushed away for the next run of cell analysis. The multi-step manipulations of human bladder cancer cells (TSGH8301) were successfully demonstrated and discussed, providing an excellent platform technology for a lab-on-a-chip (LOC).

Fabrication and characterization of nanomaterial-based sensors using dielectrophoresis

Dielectrophoresis (DEP) is an electrokinetic motion of dielectrically polarized materials in nonuniform electric fields. DEP has been successfully applied to manipulation of nanomaterials including carbon nanotubes (CNTs), metallic nanoparticles, and semiconducting nanowires. Under positive DEP force, which attracts nanomaterials toward the higher field region, nanomaterials are trapped in the electrode gap and automatically establish good electrical connections between them and the external measuring circuit. This feature allows us a fast, simple, and low-cost fabrication of nanomaterial-based sensors based on a bottom-up approach. This paper first presents a theoretical background of DEP phenomena and then reviews recent works of the present author, which were aimed to develop nanomaterial-based sensors, such as a CNT gas sensor and a ZnO nanowire photosensor, using DEP fabrication technique. It is also demonstrated that DEP technique enables self-formation of interfaces between various nanomaterials, which can be also applicable as novel sensing transducers.