Electrodeless Dielectrophoresis Research Articles

Three-dimensional molecular concentrator with micrometer-sized constriction for rapid protein enrichment

A three-dimensional electrodeless dielectrophoresis (EDEP) device incorporating a micrometer-sized constriction region is proposed for the rapid preconcentration of protein. The electrokinetic phenomena within the proposed device are investigated both numerically and experimentally. It is shown that the micro-constriction structure increases the field-focusing factor by around 15 000 times and yields a 106-fold increase in the concentration of streptavidin protein within 36 s. Overall, the proposed device provides a low-cost and effective solution for performing highly-sensitive protein detection and overcomes the Poisson statistical limit inherent in traditional two-dimensional (2D) EDEP devices through its support of large (ml-scale) sample volumes.

Combined electrokinetic manipulations of pathogenic bacterial samples in low-cost fabricated dielectrophoretic devices

A low-cost fabrication method of microfluidic devices with micrometer-sized constrictions used for electrodeless dielectrophoresis (eDEP) is demonstrated here. A structure on a commercial printed circuit board (PCB) template of one-sided copper clad fiberglass-epoxy laminate was used as a molding master for polydimethylsiloxane (PDMS) soft lithography. This was achieved by printing a constriction-based microchannel pattern on glossy paper with a micrometer-scaled resolution laser printer and transferring it to the laminate’s Cu face, rendering a microstructure of ∼17 µm height and various widths across tips. The Cu master’s pattern was transferred to PDMS, and smooth constrictions were observed under the microscope. Following air plasma encapsulation, PDMS chips were loaded with an inactivated bacterial sample of fluorescently stained Brucella abortus vaccine strain S-19 and connected to an amplified voltage source to examine the sample’s response to electric field variations. After an AC/DC electric field was applied to the bacterial solution in the microfluidic device, the combined effect of electrokinetic + hydrodynamic mechanisms that interact near the dielectric microconstrictions and exert forces to the sample was observed and later confirmed by COMSOL simulations. Our fabrication method is an alternative to be used when there is no access to advanced microfabrication facilities and opens ways for target selection and preconcentration of intracellular pathogens as well as sample preparation for metagenomics.

(Invited) Where Is Dielectrophoresis (DEP) Going?

Fifty years have passed since the first demonstration that DEP can be applied to the biomedical sciences. Pohl and Hawk [1] gave the first report of a purely physical technique being used to simultaneously distinguish and separate live and dead yeast cells. Over the past 50 years the theoretical aspects of DEP have attained a high level of refinement, whilst applications that include the manipulation of DNA, proteins, viruses, bacteria, blood cells, cancer cells and stem cells have been demonstrated. Stainless steel electrodes [1] used to generate the required high field gradients have been replaced by devices taking advantage of microfabrication and microfluidics, ranging from: microelectrode arrays [2]; insulator-based DEP [3, 4]; streaming DEP [5]; liquid electrodes [6]; carbon electrodes [7]. The key advances and relative advantages or otherwise of these various DEP techniques will be reviewed, with the aim to identify niche biomedical applications. 1. Pohl, H. A., Hawk, I. (1966) Separation of living and dead cells by dielectrophoresis, Science 152, 647-649. 2. Price, J. A. R., Burt, J. P. H., Pethig, R. (1988) Applications of a new optical technique for measuring the dielectrophoretic behaviour of micro-organisms, Biochim. Biophys. Acta 964, 221-230. 3. Masuda, S., Washizu, M., Nanba, T. (1989) Novel method of cell-fusion in field constriction area in fluid integrated circuit, IEEE Trans. Ind. Appl., 25, 732-737. 4. Chou, C-F., Tegenfeldt, J. O., Bakajin, O., Chan, S. S., Cox, E. C., Darnton, N., Duke, T., Austin, R. H. (2002) Electrodeless dielectrophoresis of single- and double-stranded DNA, Biophys. J., 83, 2170-2179. 5. Cummings, E. B., Singh, A. K. (2003) Dielectro-phoresis in microchips containing arrays of insulating posts: theoretical and experimental results, Anal. Chem., 75, 4724-4731. 6. Demierre, N., Braschler, T., Linderholm, P., Seger, U., van Lintel, H., Renaud, P. (2007) Characterization and optimization of liquid electrodes for lateral dielectro-phoresis, Lab Chip 7, 355-365. 7. Martinez-Duarte, R., Camacho-Alanis, F., Renaud, P., Ros, A. (2013) Dielectrophoresis of lambda-DNA using 3D carbon electrodes, Electrophoresis 34, 1113-1122.

Electrodeless dielectrophoresis: Impact of geometry and material on obstacle polarization.

Insulator-based (electrodeless) dielectrophoresis (iDEP) is a promising particle manipulation technique, based on movement of matter in inhomogeneous fields. The inhomogeneity of the field arises because the excitatory field distorts at obstacles (posts). This effect is caused by accumulation of polarization charges at material interfaces. In this study, we utilize a multipole expansion method to investigate the influence of geometry and material on field distortion of posts with arbitrary cross-sections in homogeneous electric fields applied perpendicular to the longitudinal axis of the post. The post then develops a multipole parallel or anti parallel to the excitatory field. The multipoles intensity is defined by the post's structure and material properties and directly influences the DEP particle trapping potential. We analyzed posts with circular and rhombus-shaped cross-sections with different cross-sectional width-to-height ratios and permittivities for their polarization intensity, multipole position, and their particle trapping behavior. A trade-off between high maximum field gradient and high coverage range of the gradient is presented, which is determined by the sharpness of the post's edges. We contribute to the overall understanding of the post polarization mechanism and expect that the results presented will help optimizing the structure of microchannels with arrays of posts for electrodeless DEP application.

On-chip DNA preconcentration in different media conductivities by electrodeless dielectrophoresis.

Electrodeless dielectrophoresis is the best choice to achieve preconcentration of nanoparticles and biomolecules due to its simple, robust, and easy implementation. We designed a simple chip with microchannels and nano-slits in between and then studied the trapping of DNA in high conductive medium and low conductive medium, corresponding to positive and negative dielectrophoresis (DEP), respectively. It is very important to investigate the trapping in media with different conductivities since one always has to deal with the sample solutions with different conductivities. The trapping process was analyzed by the fluorescent intensity changes. The results showed that DNA could be trapped at the nano-slit in both high and low conductive media in a lower electric field strength (10 V/cm) compared to the existing methods. This is a significant improvement to suppress the Joule heating effect in DEP related experiments. Our work may give insight to researchers for DNA trapping by a simple and low cost device in the Lab-on-a-Chip system.

Nanoconstriction-based electrodeless dielectrophoresis chip for nanoparticle and protein preconcentration

An electrodeless dielectrophoresis (EDEP) microchip is proposed for the concentration of nanoscale particles and proteins in a 150 nm nanoconstriction gap in a microchannel. Notably, the nanoconstriction is fabricated using a simple thermal-oxidation shrinkage process. It is shown that the nanoconstriction enhances the local electric field intensity by a factor of 1 × 103. The strong electric field and field gradient result in concentration enrichment by factors 1 × 104 and 1 × 103 for nanoparticles and proteins, respectively, within 30 s. Thus, the proposed EDEP chip has significant potential for achieving rapid and highly sensitive protein detection and for biomarker discovery applications.

Dielectrophoresis in a Slanted Microchannel for Separation of Microparticles and Bacteria

Dielectrophoresis (DEP) is an effective method to trap, manipulate and separate various dielectric particles. To generate a DEP force, a spatially nonuniform electrical field has been generated by an array of electrodes, while electrodeless DEP has been accomplished by placing an insulating material between two electrodes. Here, we describe a new DEP method for generating a nonuniform electrical field using a slanted microchannel. The electric field gradient is induced due to a slope in the channel and can be used to move and separate particles. Based on the gradual electric field induced by three dimensional structure of the microchannel, our method enables particles of different sizes to be separated solely by DEP force without flow. The slanted microchannel was easily fabricated by a replica molding technique using a commercial UV-cured photopolymer (NOA 63) and bonded as an insulating layer between two indium-tin-oxide films. By applying the electrical field, polystyrene beads of different sizes (6-45 microm in diameter) were trapped and separated depending on the applied electric strength and frequency. Using this method, the opportunistic pathogen Pseudomonas aeruginosa attached to antibody-conjugated microbeads was successfully separated from Escherichia coli in a slanted microchannel.

Characterization of Microparticle Separation Utilizing Electrokinesis within an Electrodeless Dielectrophoresis Chip

This study demonstrated the feasibility of utilizing electrokinesis in an electrodeless dielectrophoresis chip to separate and concentrate microparticles such as biosamples. Numerical simulations and experimental observations were facilitated to investigate the phenomena of electrokinetics, i.e., electroosmosis, dielectrophoresis, and electrothermosis. Moreover, the proposed operating mode can be used to simultaneously convey microparticles through a microfluidic device by using electroosmotic flow, eliminating the need for an additional micropump. These results not only revealed that the directions of fluids could be controlled with a forward/backward electroosmotic flow but also categorized the optimum separating parameters for various microparticle sizes (0.5, 1.0 and 2.0 μm). Separation of microparticles can be achieved by tuning driving frequencies at a specific electric potential (90 Vpp·cm−1). Certainly, the device can be designed as a single automated device that carries out multiple functions such as transportation, separation, and detection for the realization of the envisioned Lab-on-a-Chip idea.

Nanoscale Molecular Traps and Dams for Ultrafast Protein Enrichment in High-Conductivity Buffers

We report a new approach, molecular dam, to enhance mass transport for protein enrichment in nanofluidic channels by nanoscale electrodeless dielectrophoresis under physiological buffer conditions. Dielectric nanoconstrictions down to 30 nm embedded in nanofluidic devices serve as field-focusing lenses capable of magnifying the applied field to 10(5)-fold when combined with a micro- to nanofluidic step interface. With this strong field and the associated field gradient at the nanoconstrictions, proteins are enriched by the molecular damming effect faster than the trapping effect, to >10(5)-fold in 20 s, orders of magnitude faster than most reported methods. Our study opens further possibilities of using nanoscale molecular dams in miniaturized sensing platforms for rapid and sensitive protein analysis and biomarker discovery, with potential applications in precipitation studies and protein crystallization and possible extensions to small-molecules enrichment or screening.

Continuous and reversible mixing or demixing of nanoparticles by dielectrophoresis

Mixing and demixing (separation) are essential tasks in microfluidic devices, which seem to be contrary in nature. Accordingly, completely different strategies and devices are usually employed for their realization. We here present a microfluidic device which is capable of performing both these tasks as it can be operated in either mixing or demixing mode. The mixing and demixing processes are reversible and are accomplished by continuous operation of the device. An asymmetric S-shaped ridge extends over the full width of a microfluidic channel (200 μm) creating a constriction of 620 nm in height with an aspect ratio of 1 : 500. Appropriate AC and DC voltages generate electrodeless dielectrophoresis at the constriction as well as (linear) electrokinetic driving forces along the channel. These de/mixing parameters can be adapted in real time in such a way that continuous separation and mixing efficiencies of 85-100% can be achieved. As a proof of concept we demonstrate continuous mixing and demixing of polystyrene nanoparticles (20 and 100 nm). The experimental results are complemented by numerical simulations illustrating the particles' motion under the influence of the electrokinetic effects and thermal noise (diffusion). The monolithic one-step fabrication process by soft lithography (with PDMS in our case) will make integration and combination of several mixing and demixing functions into a more complex lab-on-a-chip device possible.

Electrodeless dielectrophoresis for bioanalysis: Theory, devices and applications

Dielectrophoresis is a non-destructive, label-free method to manipulate and separate (bio-) particles and macromolecules. The mechanism is based on the movement of polarizable objects in an inhomogeneous electric field. Here, microfluidic devices are reviewed that generate those inhomogeneous electric fields with insulating posts or constrictions, an approach called electrodeless or insulator-based dielectrophoresis. Possible advantages compared to electrode-based designs are a less complex, monolithic fabrication process with low-cost polymeric substrates and no metal surface deterioration within the area of sample analysis. The electrodeless design has led to novel devices, implementing the functionality directly into the channel geometry and covering many areas of bioanalysis, like manipulation and separation of particles, cells, DNA, and proteins.

Cover Picture: Electrophoresis 17'2011

AbstractIssue no. 17 is a special issue on “Dielectrophoresis – Part I” consisting of 16 contributions distributed over 3 distinct parts. “We are delighted to start a new tradition of special issues on Dielectrophoresis, a novel and powerful technique that is increasingly gaining significant interest from both the academic and the industrial communities.” The present special issue assembles “valuable contributions from research groups in USA, Europe, Asia and Latin America. The articles cover the fundamentals of dielectrophoresis, extending to applications for nanoscale particles, with focus on protein characterization, to a wide array of systems for the separation and sorting of a variety of cells.”“The first section on Fundamentals includes three valuable review articles covering the topics of double layer polarization, liquid dielectrophoresis and two phase flow, and an overview of electrodeless dielectrophoresis with focus on bioanalysis. The second section of this issue is focused on nanoscale dielectrophoresis, starting with a review article that analyzes the state of the art on the dielectrophoretic manipulation of a wide range of nanosized particles, from semiconducting particles, to DNA, nanowires and graphene. This review article is followed by two contributions on the manipulation of protein particles in iDEP systems, extending to experimental and numerical simulation studies.The third and last section is focused on the dielectrophoretic manipulation of cells. The section begins with a review article that examines the latest developments of dielectrophoresis for monitoring microorganisms in environmental applications. The review includes applications for water, air and soil assessments that study a large variety of microorganisms, from virus to protozoa. The review is followed by contributions extending to several modes and configurations for applying dielectrophoresis, comprising nanoelectrodes, 3‐D microstructures, cascade systems, 3‐D carbon electrodes and microwell electrodes. The remarkable response received for this special issue confirms the powerful impact of dielectrophoresis on the field of microfluidics. ‘Dielectrophoresis 2011 – Part II’ will be published in the upcoming issue no. 18.”Featured articles include:Dielectrophoretic mobility determination in DC insulator‐based dielectrophoresis. ((10.1002/elps.201100034))Dielectrophoresis at the nanoscale. ((10.1002/elps.201100038))A novel approach to dielectrophoresis using carbon electrodes. ((10.1002/elps.201100059))

DC insulator dielectrophoretic applications in microdevice technology: a review

Dielectrophoresis is a noninvasive, nondestructive, inexpensive, and fast technique for the manipulation of bioparticles. Recent advances in the field of dielectrophoresis (DEP) have resulted in new approaches for characterizing the behavior of particles and cells using direct current (DC) electric fields. In such approaches, spatial nonuniformities are created in the channel by embedding insulating obstacles in the channel or flow field in order to perform separation or trapping. This emerging field of dielectrophoresis is commonly termed DC insulator dielectrophoresis (DC-iDEP), insulator-based dielectrophoresis (iDEP), or electrodeless dielectrophoresis (eDEP). In many microdevices, this form of dielectrophoresis has advantages over traditional AC-DEP, including single material microfabrication, remotely positioned electrodes, and reduced fouling of the test region. DC-iDEP applications have included disease detection, separation of cancerous cells from normal cells, and separation of live from dead bacteria. However, there is a need for a critical report to integrate these important research findings. The aim of this review is to provide an overview of the current state-of-art technology in the field of DC-iDEP for the separation and trapping of inert particles and cells. In this article, a review of the concepts and theory leading to the manipulation of particles via DC-iDEP is given, and insulating obstacle geometry designs and the characterization of device performance are discussed. This review compiles and compares the significant findings obtained by researchers in handling and manipulating particles.

Dielectrophoretic Manipulation of DNA: Separation and Polarizability

Although separation of polymers based on the combination of dielectrophoretic trapping and electrophoretic forces was proposed 15 years ago, experimental proof has not yet been reported. Here, we address this problem for long DNA fragments in a simple and easy-to-fabricate microfluidic device, in which the DNA is manipulated by electrophoresis and by electrodeless dielectrophoresis. By slowly increasing the strength of the dielectrophoretic traps in the course of the separation experiments, we are able to perform efficient and fast DNA separation according to length for two different DNA conformations: linear DNA (lambda (48.5-kbp) and T2 (164-kbp) DNA) and supercoiled covalently closed circular plasmid DNA (7 and 14 kbp). The underlying migration mechanism-thermally induced escape processes out of the dielectrophoretic traps in the direction of the electrophoretic force-is sensitive to different DNA fragments because of length-dependent DNA polarizabilities. This is analyzed in a second series of experiments, where the migration mechanism is exploited for the quantitative measurement of the DNA polarizabilities. This new and simple technique allows for the systematic characterization of the polarizability not only for DNA but also for other biomolecules like proteins. Furthermore, our results have direct implications to future biotechnological applications such as gene therapy and DNA vaccination.

Device Structure for enhancement of DNA hybridization kinetics by Electrodeless Dielectrophoresis

ABSTRACTSignal transduction for purposes of biomolecular sensing can be enhanced through miniaturization (nanoscale sensors such as nanowires, cantilevers, etc), but this may impose insurmountable limitations on transport of analyte molecules to the surface. In order to improve biomolecular detection sensitivity, this study aims to develop electrodeless dielectrophoresis (EDEP) methods for the selective transport and trapping of analytes in close proximity to the sensor surface. A device design based on microscale dielectric constrictions of the fluidic channel and nanoscale metal electrode edges was used to locally enhance electric field gradients and trap biomolecules. The resulting electric field focusing effect was enhanced as a result of miniaturization and an instantaneous ten-fold EDEP preconcentration was obtained in high-salt buffers (50 mM NaCl) that enabled an equivalent improvement in DNA hybridization kinetics.

Electrodeless Dielectrophoresis of Single- and Double-Stranded DNA

Dielectrophoretic trapping of molecules is typically carried out using metal electrodes to provide high field gradients. In this paper we demonstrate dielectrophoretic trapping using insulating constrictions at far lower frequencies than are feasible with metallic trapping structures because of water electrolysis. We demonstrate that electrodeless dielectrophoresis (EDEP) can be used for concentration and patterning of both single-strand and double-strand DNA. A possible mechanism for DNA polarization in ionic solution is discussed based on the frequency, viscosity, and field dependence of the observed trapping force.