Insulator-based dielectrophoretic single particle and single cancer cell trapping

On the behavior of sub-micrometer polystyrene particles subjected to AC insulator-based dielectrophoresis

Polymer beads, especially polystyrene particles, have been extensively used as model species in insulator-based dielectrophoresis (iDEP) studies. Their use in alternating current iDEP (AC-iDEP) is less explored; however, an assessment in the low-frequency regime (≤10 kHz) allows to link surface conduction effects with the surface properties of polymer particles. Here, we provide a case study for various experimental conditions assessing sub-micrometer polystyrene particles with AC-iDEP and link to accepted surface conduction theory to predict and experimentally verify the observed AC-iDEP trapping behavior based on apparent zeta potential and solution conductivity. We find excellent agreement with the theoretical predictions, but also the occurrence of concentration polarization electroosmotic flow under the studied conditions, which have the potential to confound acting dielectrophoresis conditions. Furthermore, we study a case relevant to the assessment of microplastics in human and animal body fluids by mimicking the protein adsorption of high abundant proteins in blood by coating polystyrene beads with bovine serum albumin, a highly abundant protein in blood. Theoretical predictions and experimental observations confirm a difference in observed AC-iDEP behavior between coated and non-coated particles, which might be exploited for future studies of microplastics in blood to assess their exposure to humans and animals.

A correlation of conductivity medium and bioparticle viability on dielectrophoresis-based biomedical applications

Dielectrophoresis (DEP) bioparticle research has progressed from micro to nano levels. It has proven to be a promising and powerful cell manipulation method with an accurate, quick, inexpensive, and label-free technique for therapeutic purposes. DEP, an electrokinetic phenomenon, induces particle movement as a result of polarization effects in a nonuniform electrical field. This review focuses on current research in the biomedical field that demonstrates a practical approach to DEP in terms of cell separation, trapping, discrimination, and enrichment under the influence of the conductive medium in correlation with bioparticle viability. The current review aims to provide readers with an in-depth knowledge of the fundamental theory and principles of the DEP technique, which is influenced by conductive medium and to identify and demonstrate the biomedical application areas. The high conductivity of physiological fluids presents obstacles and opportunities, followed by bioparticle viability in an electric field elaborated in detail. Finally, the drawbacks of DEP-based systems and the outlook for the future are addressed. This article will aid in advancing technology by bridging the gap between bioscience and engineering. We hope the insights presented in this review will improve cell suspension medium and promote DEP-viable bioparticle manipulation for health-care diagnostics and therapeutics.

Controlled Transport of Individual Microparticles Using Dielectrophoresis

A dielectrophoretic device employing a planar array of microelectrodes is designed for controlled transport of individual microparticles. By exciting the electrodes in sequence, a moving dielectrophoretic force is created that can drag a particle across the electrodes in a straight line. The electrode shapes are designed to counter any lateral drift of the trapped particle during transport. This facilitates single particle transport by creating a narrow two-dimensional corridor for the moving dielectrophoretic force to operate on. The design and analysis processes are discussed in detail. Numerical simulations are performed to calculate the electromagnetic field distribution and the generated dielectrophoretic force near the electrodes. The Langevin equation is used for analyzing the trajectory of a microparticle under the influence of the external forces. The simulations show how the designed electrode geometry produces the necessary lateral confinement required for successful particle transport. Finally, experimental results are presented showing controlled bidirectional linear transport of single polystyrene beads of radius 10 and 5 μm for a distances 840 and 1100 μm, respectively. The capabilities of the proposed platform make it suitable for micro total analysis systems (μTAS) and lab-on-a-chip (LOC) applications.

The latest advances on nonlinear insulator-based electrokinetic microsystems under direct current and low-frequency alternating current fields: a review

This review article presents an overview of the evolution of the field of insulator-based dielectrophoresis (iDEP); in particular, it focuses on insulator-based electrokinetic (iEK) systems stimulated with direct current and low-frequency(< 1 kHz) AC electric fields. The article covers the surge of iDEP as a research field where many different device designs were developed, from microchannels with arrays of insulating posts to devices with curved walls and nano- and micropipettes. All of these systems allowed for the manipulation and separation of a wide array of particles, ranging from macromolecules to microorganisms, including clinical and biomedical applications. Recent experimental reports, supported by important theoretical studies in the field of physics and colloids, brought attention to the effects of electrophoresis of the second kind in these systems. These recent findings suggest that DEP is not the main force behind particle trapping, as it was believed for the last two decades. This new research suggests that particle trapping, under DC and low-frequency AC potentials, mainly results from a balance between electroosmotic and electrophoretic effects (linear and nonlinear); although DEP is present in these systems, it is not a dominant force. Considering these recent studies, it is proposed to rename this field from DC-iDEP to DC-iEK (and low-frequency AC-iDEP to low-frequency AC-iEK). Whereas much research is still needed, this is an exciting time in the field of microscale EK systems, as these new findings seem to explain the challenges with modeling particle migration and trapping in iEK devices, and provide perhaps a better understanding of the mechanisms behind particle trapping.

Insulator Based Dielectrophoresis: Micro, Nano, and Molecular Scale Biological Applications

Insulator based dielectrophoresis (iDEP) is becoming increasingly important in emerging biomolecular applications, including particle purification, fractionation, and separation. Compared to conventional electrode-based dielectrophoresis (eDEP) techniques, iDEP has been demonstrated to have a higher degree of selectivity of biological samples while also being less biologically intrusive. Over the past two decades, substantial technological advances have been made, enabling iDEP to be applied from micro, to nano and molecular scales. Soft particles, including cell organelles, viruses, proteins, and nucleic acids, have been manipulated using iDEP, enabling the exploration of subnanometer biological interactions. Recent investigations using this technique have demonstrated a wide range of applications, including biomarker screening, protein folding analysis, and molecular sensing. Here, we review current state-of-art research on iDEP systems and highlight potential future work.

Length-Selective Dielectrophoretic Manipulation of Single-Walled Carbon Nanotubes

Single-walled carbon nanotubes (SWNTs) possess unique physical, optical, and electrical properties with great potential for future nanoscale device applications. Common synthesis procedures yield SWNTs with large length polydispersity and varying chirality. Electrical and optical applications of SWNTs often require specific lengths, but the preparation of SWNTs with the desired length is still challenging. Insulator-based dielectrophoresis (iDEP) integrated into a microfluidic device has the potential to separate SWNTs by length. Semiconducting SWNTs of varying length suspended with sodium deoxycholate (NaDOC) show unique dielectrophoretic properties at low frequencies (<1 kHz) that were exploited here using an iDEP-based microfluidic constriction sorter device for length-based sorting. Specific migration directions in the constriction sorter were induced for long SWNTs (≥1000 nm) with negative dielectrophoretic properties compared to short (≤300 nm) SWNTs with positive dielectrophoretic properties. We report continuous fractionation conditions for length-based iDEP migration of SWNTs, and we characterize the dynamics of migration of SWNTs in the microdevice using a finite element model. Based on the length and dielectrophoretic characteristics, sorting efficiencies for long and short SWNTs recovered from separate channels of the constriction sorter amounted to >90% and were in excellent agreement with a numerical model for the sorting process.

Selective Manipulation of Biomolecules with Insulator-Based Dielectrophoretic Tweezers

Insulator-based dielectrophoretic (iDEP) trapping, separating, and concentrating nanoscale objects is carried out using a non-metal, unbiased, mobile tip acing as a tweezers. The spatial control and manipulation of fluorescently-labeled polystyrene particles and DNA were performed to demonstrate the feasibility of the iDEP tweezers. Frequency-dependent iDEP tweezers' strength and polarity were quantitatively determined using two theoretical approaches to DNA, which resulted in a factor of 2 ~ 40 differences between them. In either approach, the strength of iDEP was at least 4-order of magnitude stronger than the thermal force, indicating iDEP was a dominant force for trapping, holding, and separating DNA. The trapping strength and volume of the iDEP tweezers were also determined, which further supports direct capture and manipulation of DNA at the tip end.

Emerging microfluidic devices for cancer cells/biomarkers manipulation and detection

Circulating tumour cells (CTCs) are active participants in the metastasis process and account for ∼90% of all cancer deaths. As CTCs are admixed with a very large amount of erythrocytes, leukocytes, and platelets in blood, CTCs are very rare, making their isolation, capture, and detection a major technological challenge. Microfluidic technologies have opened-up new opportunities for the screening of blood samples and the detection of CTCs or other important cancer biomarker-proteins. In this study, the authors have reviewed the most recent developments in microfluidic devices for cells/biomarkers manipulation and detection, focusing their attention on immunomagnetic-affinity-based devices, dielectrophoresis-based devices, surface-plasmon-resonance microfluidic sensors, and quantum-dots-based sensors.

Deterministic Absolute Negative Mobility for Micro- and Submicrometer Particles Induced in a Microfluidic Device

Efficient separations of particles with micron and submicron dimensions are extremely useful in preparation and analysis of materials for nanotechnological and biological applications. Here, we demonstrate a nonintuitive, yet efficient, separation mechanism for μm and subμm colloidal particles and organelles, taking advantage of particle transport in a nonlinear post array in a microfluidic device under the periodic action of electrokinetic and dielectrophoretic forces. We reveal regimes in which deterministic particle migration opposite to the average applied force occurs for a larger particle, a typical signature of deterministic absolute negative mobility (dANM), whereas normal response is obtained for smaller particles. The coexistence of dANM and normal migration was characterized and optimized in numerical modeling and subsequently implemented in a microfluidic device demonstrating at least 2 orders of magnitude higher migration speeds as compared to previous ANM systems. We also induce dANM for mouse liver mitochondria and envision that the separation mechanisms described here provide size selectivity required in future separations of organelles, nanoparticles, and protein nanocrystals.

Isolation and enrichment of low abundant particles with insulator-based dielectrophoresis

Isolation and enrichment of low-abundant particles are essential steps in many bio-analytical and clinical applications. In this work, the capability of an insulator-based dielectrophoresis (iDEP) device for the detection and stable capture of low abundant polystyrene particles and yeast cells was evaluated. Binary and tertiary mixtures of particles and cells were tested, where the low-abundant particles had concentration ratios on the order of 1:10 000 000 compared to the other particles present in the mixture. The results demonstrated successful and stable capture and enrichment of rare particles and cells (trapping efficiencies over 99%), where particles remained trapped in a stable manner for up to 4 min. A device with four reservoirs was employed for the separation and enrichment of rare particles, where the particles of interest were first selectively concentrated and then effectively directed to a side port for future collection and analysis. The present study demonstrates that simple iDEP devices have appropriate screening capacity and can be used for handling samples containing rare particles; achieving both enrichment and isolation of low-abundant particles and cells.

Microfluidic sorting of protein nanocrystals by size for X-ray free-electron laser diffraction

The advent and application of the X-ray free-electron laser (XFEL) has uncovered the structures of proteins that could not previously be solved using traditional crystallography. While this new technology is powerful, optimization of the process is still needed to improve data quality and analysis efficiency. One area is sample heterogeneity, where variations in crystal size (among other factors) lead to the requirement of large data sets (and thus 10-100 mg of protein) for determining accurate structure factors. To decrease sample dispersity, we developed a high-throughput microfluidic sorter operating on the principle of dielectrophoresis, whereby polydisperse particles can be transported into various fluid streams for size fractionation. Using this microsorter, we isolated several milliliters of photosystem I nanocrystal fractions ranging from 200 to 600 nm in size as characterized by dynamic light scattering, nanoparticle tracking, and electron microscopy. Sorted nanocrystals were delivered in a liquid jet via the gas dynamic virtual nozzle into the path of the XFEL at the Linac Coherent Light Source. We obtained diffraction to ∼4 Å resolution, indicating that the small crystals were not damaged by the sorting process. We also observed the shape transforms of photosystem I nanocrystals, demonstrating that our device can optimize data collection for the shape transform-based phasing method. Using simulations, we show that narrow crystal size distributions can significantly improve merged data quality in serial crystallography. From this proof-of-concept work, we expect that the automated size-sorting of protein crystals will become an important step for sample production by reducing the amount of protein needed for a high quality final structure and the development of novel phasing methods that exploit inter-Bragg reflection intensities or use variations in beam intensity for radiation damage-induced phasing. This method will also permit an analysis of the dependence of crystal quality on crystal size.

Development of the resolution theory for gradient insulator-based dielectrophoresis

New and important separations capabilities are being enabled by utilizing other electric field-induced forces besides electrophoresis, among these is dielectrophoresis. Recent works have used experimentally simple insulator-based systems that induce field gradients creating dielectrophoretic force in useful formats. Among these, juxtaposing forces can generate gradient-based steady-state separations schemes globally similar to isoelectric focusing. The system of interest is termed gradient insulator-based dielectrophoresis and can create extremely high resolution steady-state separations for particles four nanometers to ten micrometers in diameter, including nearly all important bioparticles (large proteins, protein aggregates, polynucleotides viruses, organelles, cells, bacteria, etc.). A theoretical underpinning is developed here to understand the relationship between experimental parameters and resolution and to identify the best expected resolution possible. According to the results, differences in particles (and bioparticles) as small as one part in 10(4) for diameter (subnanometer resolution for a one micrometer particle), one part in 10(8) for dielectrophoretic parameters (dielectrophoretic mobility, Clausius-Mossotti factor), and one part in 10(5) for electrophoretic mobility can be resolved. These figures of merit are generally better than any competing technique, in some cases by orders of magnitude. This performance is enabled by very strong focusing forces associated with localized gradients.

The Cytoprotective Effect of Petalonia binghamiae Methanol Extract against Oxidative Stress in C2C12 Myoblasts: Mediation by Upregulation of Heme Oxygenase-1 and Nuclear Factor-Erythroid 2 Related Factor 2

This study was designed to examine the protective effects of the marine brown algae Petalonia binghamiae against oxidative stress-induced cellular damage and to elucidate the underlying mechanisms. P. binghamiae methanol extract (PBME) prevented hydrogen peroxide (H2O2)-induced growth inhibition and exhibited scavenging activity against intracellular reactive oxygen species (ROS) induced by H2O2 in mouse-derived C2C12 myoblasts. PBME also significantly attenuated H2O2-induced comet tail formation in a comet assay, histone γH2A.X phosphorylation, and annexin V-positive cells, suggesting that PBME prevented H2O2-induced cellular DNA damage and apoptotic cell death. Furthermore, PBME increased the levels of heme oxygenase-1 (HO-1), a potent antioxidant enzyme, associated with the induction of nuclear factor-erythroid 2 related factor 2 (Nrf2). However, zinc protoporphyrin IX, a HO-1 competitive inhibitor, significantly abolished the protective effects of PBME on H2O2-induced ROS generation, growth inhibition, and apoptosis. Collectively, these results demonstrate that PBME augments the antioxidant defense capacity through activation of the Nrf2/HO-1 pathway.

Dielectrophoretic concentrator enhancement based on dielectric poles for continuously flowing samples

We describe a novel continuous-flow cell concentrator microdevice based on dielectrophoresis, and its associated custom-made control unit. The performances of a classical interdigitated metal electrode-based dielectrophoresis microfluidic device and this enhanced version, that includes insulator-based pole structures, were compared using the same setup. Escherichia coli samples were concentrated at several continuous flows and the device's trapping efficiencies were evaluated by exhaustive cell counts. Our results show that pole structures enhance the retention up to 12.6%, obtaining significant differences for flow rates up to 20 μL/min, when compared to an equivalent classical interdigitated electrodes setup. In addition, we performed a subsequent proteomic analysis to evaluate the viability of the biological samples after the long exposure to the actuating electrical field. No Escherichia coli protein alteration in any of the two systems was observed.

Insulator-based dielectrophoresis of mitochondria

Isolated mitochondria display a wide range of sizes plausibly resulting from the coexistence of subpopulations, some of which may be associated with disease or aging. Strategies to separate subpopulations are needed to study the importance of these organelles in cellular functions. Here, insulator-based dielectrophoresis (iDEP) was exploited to provide a new dimension of organelle separation. The dielectrophoretic properties of isolated Fischer 344 (F344) rat semimembranosus muscle mitochondria and C57BL/6 mouse hepatic mitochondria in low conductivity buffer (0.025-0.030 S/m) at physiological pH (7.2-7.4) were studied using polydimethylsiloxane (PDMS) microfluidic devices. First, direct current (DC) and alternating current (AC) of 0-50 kHz with potentials of 0-3000 V applied over a channel length of 1 cm were separately employed to generate inhomogeneous electric fields and establish that mitochondria exhibit negative DEP (nDEP). DEP trapping potential thresholds at 0-50 kHz were also determined to be weakly dependent on applied frequency and were generally above 200 V. Second, we demonstrated a separation scheme using DC potentials <100 V to perform the first size-based iDEP sorting of mitochondria. Samples of isolated mitochondria with heterogeneous sizes (150 nm-2 μm diameters) were successfully separated into sub-micron fractions, indicating the ability to isolate mitochondria into populations based on their size.

Dynamic microparticle manipulation with an electroosmotic flow gradient in low-frequency alternating current dielectrophoresis

In this study, the potential of low-frequency AC insulator-based DEP (iDEP) was explored for the separation of polystyrene microparticles and yeast cells. An EOF gradient was generated by employing an asymmetrical, 20 Hz AC electrical signal in an iDEP device consisting of a microchannel with diamond-shaped insulating posts. Two types of samples were analyzed, the first sample contained three types of polystyrene particles with different diameters (0.5, 1.0, and 2.0 μm) and the second sample contained two types of polystyrene particles (1.0 and 2 μm) and yeast cells (6.3 μm). This particular scheme uses a tapered AC signal that allows for all particles to be trapped and concentrated at the insulating post array, as the signal becomes asymmetrical (more positive), particles are selectively released. The smallest particles in each sample were released first, since they require greater dielectrophoretic forces to remain trapped. The largest particles in each sample were released last, when the applied signal became cyclical. A dielectropherogram, which is analogous to a chromatogram, was obtained for each sample, demonstrating successful separation of the particles by showing "peaks" of the released particles. These separations were achieved at lower applied potentials than those reported in previous studies that used solely direct current electrical voltages. Additionally, mathematical modeling with COMSOL Multiphysics was carried out to estimate the magnitude of the dielectrophoretic and EOF forces acting on the particles considering the low-frequency, asymmetrical AC signal used in the experiments. The results demonstrated the potential of low-frequency AC-iDEP systems for handling and separating complex mixtures of microparticles and biological cells.

Integrated sorting, concentration and real time PCR based detection system for sensitive detection of microorganisms

The extremely low limit of detection (LOD) posed by global food and water safety standards necessitates the need to perform a rapid process of integrated detection with high specificity, sensitivity and repeatability. The work reported in this article shows a microchip platform which carries out an ensemble of protocols which are otherwise carried in a molecular biology laboratory to achieve the global safety standards. The various steps in the microchip include pre-concentration of specific microorganisms from samples and a highly specific real time molecular identification utilizing a q-PCR process. The microchip process utilizes a high sensitivity antibody based recognition and an electric field mediated capture enabling an overall low LOD. The whole process of counting, sorting and molecular identification is performed in less than 4 hours for highly dilute samples.

Quantitative dielectrophoretic tracking for characterization and separation of persistent subpopulations of Cryptosporidium parvum

Microbial persistence to antibiotics is attributed to subpopulations with phenotypic variations that cause a spread of susceptibility levels, leading to the recurrence of infections and stability of biofilms. Herein, persistent oocyst subpopulations identified by animal infectivity and excystation assays during the disinfection of Cryptosporidium parvum, a water-borne pathogen capable of causing enteric infections at ultra-low doses, are separated and characterized by quantitative dielectrophoretic tracking over a wide frequency range (10 kHz-10 MHz). To enable the simultaneous and facile dielectrophoretic tracking of individual oocysts, insulator constrictions in a microfluidic channel are utilized to spatially modulate the localized field over the extent needed for defining oocyst trajectories and for obtaining high-resolution displacement versus time measurements under both, positive and negative dielectrophoresis. In this manner, by obviating the need for averaging dielectrophoretic data over a large collection region, the force response is more sensitive to differences in electrophysiology from sub-population fractions. Hence, the electrophysiology of sensitive and persistent oocysts after heat and silver nanoparticle treatments can be quantified by correlating the force response at low frequencies (<100 kHz) to the integrity of the oocyst wall and at high frequencies (0.4-1 MHz) to the sporozoites in the oocyst. This label-free method can characterize heterogeneous microbial samples with subpopulations of phenotypically different alterations, for quantifying the intensity of alteration and fraction with a particular alteration type.

Dielectrophoretic sorting of membrane protein nanocrystals

Structure elucidation of large membrane protein complexes is still a considerable challenge, yet is a key factor in drug development and disease combat. Femtosecond nanocrystallography is an emerging technique with which structural information of membrane proteins is obtained without the need to grow large crystals, thus overcoming the experimental riddle faced in traditional crystallography methods. Here, we demonstrate for the first time a microfluidic device capable of sorting membrane protein crystals based on size using dielectrophoresis. We demonstrate the excellent sorting power of this new approach with numerical simulations of selected submicrometer beads in excellent agreement with experimental observations. Crystals from batch crystallization broths of the huge membrane protein complex photosystem I were sorted without further treatment, resulting in a high degree of monodispersity and crystallinity in the ~100 nm size range. Microfluidic integration, continuous sorting, and nanometer-sized crystal fractions make this method ideal for direct coupling to femtosecond nanocrystallography.

Characterization of a hybrid dielectrophoresis and immunocapture microfluidic system for cancer cell capture

The capture of circulating tumor cells (CTCs) from cancer patient blood enables early clinical assessment as well as genetic and pharmacological evaluation of cancer and metastasis. Although there have been many microfluidic immunocapture and electrokinetic techniques developed for isolating rare cancer cells, these techniques are often limited by a capture performance tradeoff between high efficiency and high purity. We present the characterization of shear-dependent cancer cell capture in a novel hybrid DEP-immunocapture system consisting of interdigitated electrodes fabricated in a Hele-Shaw flow cell that was functionalized with a monoclonal antibody, J591, which is highly specific to prostate-specific membrane antigen expressing prostate cancer cells. We measured the positive and negative DEP response of a prostate cancer cell line, LNCaP, as a function of applied electric field frequency, and showed that DEP can control capture performance by promoting or preventing cell interactions with immunocapture surfaces, depending on the sign and magnitude of the applied DEP force, as well as on the local shear stress experienced by cells flowing in the device. This work demonstrates that DEP and immunocapture techniques can work synergistically to improve cell capture performance, and it will aid in the design of future hybrid DEP-immunocapture systems for high-efficiency CTC capture with enhanced purity.

Advances of lab-on-a-chip in isolation, detection and post-processing of circulating tumour cells

Circulating tumour cells (CTCs) are shed by primary tumours and are found in the peripheral blood of patients with metastatic cancers. Recent studies have shown that the number of CTCs corresponds with disease severity and prognosis. Therefore, detection and further functional analysis of CTCs are important for biomedical science, early diagnosis of cancer metastasis and tracking treatment efficacy in cancer patients, especially in point-of-care applications. Over the last few years, there has been an increasing shift towards not only capturing and detecting these rare cells, but also ensuring their viability for post-processing, such as cell culture and genetic analysis. High throughput lab-on-a-chip (LOC) has been fuelled up to process and analyse heterogeneous real patient samples while gaining profound insights for cancer biology. In this review, we highlight how miniaturisation strategies together with nanotechnologies have been used to advance LOC for capturing, separating, enriching and detecting different CTCs efficiently, while meeting the challenges of cell viability, high throughput multiplex or single-cell detection and post-processing. We begin this survey with an introduction to CTC biology, followed by description of the use of various materials, microstructures and nanostructures for design of LOC to achieve miniaturisation, as well as how various CTC capture or separation strategies can enhance cell capture and enrichment efficiencies, purity and viability. The significant progress of various nanotechnologies-based detection techniques to achieve high sensitivities and low detection limits for viable CTCs and/or to enable CTC post-processing are presented and the fundamental insights are also discussed. Finally, the challenges and perspectives of the technologies are enumerated.

Microfluidic devices for high-throughput proteome analyses

Over the last decades, microfabricated bioanalytical platforms have gained enormous interest due to their potential to revolutionize biological analytics. Their popularity is based on several key properties, such as high flexibility of design, low sample consumption, rapid analysis time, and minimization of manual handling steps, which are of interest for proteomics analyses. An ideal totally integrated chip-based microfluidic device could allow rapid automated workflows starting from cell cultivation and ending with MS-based proteome analysis. By reducing or eliminating sample handling and transfer steps and increasing the throughput of analyses these workflows would dramatically improve the reliability, reproducibility, and throughput of proteomic investigations. While these complete devices do not exist for routine use yet, many improvements have been made in the translation of proteomic sample handling and separation steps into microfluidic formats. In this review, we will focus on recent developments and strategies to enable and integrate proteomic workflows into microfluidic devices.

Microcapillary-assisted dielectrophoresis for single-particle positioning

Here, we demonstrate microcapillary-assisted dielectrophoresis (μC-DEP), a new capability for precise positioning of particles or biological cells in applications such as dynamic assays. The method largely derives from a need to evade the challenges faced with hydrodynamic trapping of particles or cells at microcapillaries typically realized through brief application of suction. Microcapillaries here serve a dual purpose by firstly squeezing field lines to define localized positive DEP traps and then establishing an exclusive access to the trapped cell for probing. Strength of the traps is presented through numerical results at various excitation frequencies. Their effectiveness is shown experimentally against relevant solution conductivities using 10 μm polystyrene microspheres. Usefulness of the method for positioning individual cells is demonstrated via experimental results on cell viability and single-cell impedance spectroscopy.