Aytug Gencoglu

DC insulator dielectrophoretic applications in microdevice technology: a review

AbstractDielectrophoresis 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. FigureCommon insulating obstacle geometries reported in the literature. Red zones indicate where the particles experience the maximum dielectrophoretic effect under DC or DC plus AC-biased electric field conditions

Quantification of pH gradients and implications in insulator-based dielectrophoresis of biomolecules.

Direct current (DC) insulator‐based dielectrophoretic (iDEP) microdevices have the potential to replace traditional alternating current dielectrophoretic devices for many cellular and biomolecular separation applications. The use of large DC fields suggest that electrode reactions and ion transport mechanisms can become important and impact ion distributions in the nanoliters of fluid in iDEP microchannels. This work tracked natural pH gradient formation in a 100 μm wide, 1 cm‐long microchannel under applicable iDEP protein manipulation conditions. Using fluorescence microscopy with the pH‐sensitive dye FITC Isomer I and the pH‐insensitive dye TRITC as a reference, pH was observed to drop drastically in the microchannels within 1 min in a 3000 V/cm electric field; pH drops were observed in the range of 6–10 min within a 100 V/cm electric field and varied based on the buffer conductivity. To address concerns of dye transport impacting intensity data, electrokinetic mobilities of FITC were carefully examined and found to be (i) toward the anode and (ii) 1 to 2 orders of magnitude smaller than H+ transport which is responsible for pH drops from the anode toward the cathode. COMSOL simulations of ion transport showed qualitative agreement with experimental results. The results indicate that pH changes are severe enough and rapid enough to influence the net charge of a protein or cause aggregation during iDEP experiments. The results also elucidate reasonable time periods over which the phosphate buffering capacity can counter increases in H+ and OH− for unperturbed iDEP manipulations.

Effect of insulating posts geometry on particle manipulation in insulator based dielectrophoretic devices.

In this study, the effect of the geometry of insulating posts on microparticle trapping in insulator based dielectrophoresis (iDEP) was analyzed. The motivation for this research was to study how to improve particle trapping and enrichment by modifying the shape of insulating posts used in iDEP microdevices, while keeping post spacing constant. Mixtures of inert polystyrene particles were employed for demonstrating the effects of insulator shape on particle capture and enrichment. A series of experiments were carried out using an array of devices with different insulating post shapes. All the different post shapes employed had a width of 200 μm and were arranged in a square array of 250 μm center-to-center, thus, the spacing between posts was 50 μm in all cases. Mathematical modeling with COMSOL Multiphysics was employed to assess the magnitude of electric field gradients achieved with each one of the geometries tested. The results showed that the electric potential required to obtain effective particle trapping and enrichment can be significantly reduced by modifying the geometry of the insulating posts, without having to modify the separation distance between posts, thus, preserving the porosity of the microchannels. The separation of a mixture of 1-μm and 2-μm diameter particles was achieved in the form of dielectropherograms employing two different insulating post geometries (circle and diamond). Concentrated particles were released as peaks from the insulating post arrays where higher peak resolution separation was obtained with the sharper diamond geometry. Concentration enrichment above one order or magnitude was obtained for both particle types in both dielectropherograms. The results demonstrate that more efficient iDEP separations can be achieved at lower applied electric potentials by carefully selecting the geometry of the insulating structures.

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.

Dielectrophoretic manipulation of particle mixtures employing asymmetric insulating posts

A novel scheme for particle separation with insulator‐based dielectrophoresis (iDEP) was developed. This technique offers the capability for an inverted order in particle elution, where larger particles leave the system before smaller particles. Asymmetrically shaped insulating posts, coupled with direct current (DC) biased low‐frequency alternating current (AC) electric potentials, were used to successfully separate a mixture of 500 nm and 1 μm polystyrene particles (size difference of 0.5 μm in diameter). In this separation, the 1 μm particles were eluted first, demonstrating the discriminatory potential of this methodology. To extend this technique to biological samples, a mixture containing Saccharomyces cerevisiae cells (6.3 μm) and 2 μm polystyrene particles was also separated, with the cells being eluted first. The asymmetric posts featured a shorter sharp half and a longer blunt half; this produced an asymmetry in the forces exerted on the particles. The negative DC offset produced a net displacement of the smaller particles toward the upstream direction, while the post asymmetry produced a net displacement of the larger particles toward the downstream direction. This new iDEP approach provides a setup where larger particles are quickly concentrated at the outlet of the post array and can be released first when in a mixture with smaller particles. This new scheme offers an extra set of parameters (alternating current amplitude, DC offset, post asymmetry, and shape) that can be manipulated to obtain a desired separation. This asymmetric post iDEP technique has potential for separations where it is important to quickly elute and enrich larger and more fragile cells in biological samples.

Particle Manipulation in Dielectrophoretic Devices

Microfluidic devices or lab-on-a-chip systems can make a significant impact in many fields where obtaining a rapid response is critical, particularly in analyses involving biological cells. Microfluidics has revolutionized the manner in which many different assessments/processes are carried out, since it offers attractive advantages over traditional bench-scale techniques. Some of the advantages are: small sample and reagent amounts, higher resolution and sensitivity, improved level of integration and automation, lower cost and much shorter processing times. There is a growing interest on the development of techniques that can be used in microfluidics devices. Among these, electrokinetic techniques have shown great potential due to their flexibility. Dielectrophoresis (DEP) is an electrokinetic mechanism that refers to the interaction of a dielectric particle with a spatially non-uniform electric field; this leads to particle movement due to polarization effects. DEP offers great potential since it can be carried out employing DC and AC electric fields, and neutral and charged particles can be manipulated. This work is focused on the use of insulator based DEP (iDEP), a novel dielectrophoretic mode that employs arrays of insulating structures to generate dielectrophoretic forces. Successful microparticle manipulation can be achieved employing iDEP, due to its unique characteristics that allow for great flexibility. In this work, microchannels containing arrays of cylindrical insulating posts were employed to concentrate, sort and separate microparticles. Mathematical modeling with COMSOL® was performed to identify optimal device configuration. Different sets of experiments were carried out employing DC and AC potentials. The results demonstrated that effective and fast particle manipulation is possible by fine tuning dielectrophoretic force and electroosmotic flow.Copyright