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.

In recent years, dielectrophoretic force has been used to manipulate colloids, inert particles, and biological microparticles, such as red blood cells, white blood cells, platelets, cancer cells, bacteria, yeast, microorganisms, proteins, DNA, etc. This specific electrokinetic technique has been used for trapping, sorting, focusing, filtration, patterning, assembly, and separating biological entities/particles suspended in a buffer medium. Dielectrophoretic forces acting on particles depend on various parameters, for example, charge of the particle, geometry of the device, dielectric constant of the medium and particle, and physiology of the particle. Therefore, to design an effective micro-/nanofluidic separation platform, it is necessary to understand the role of the aforementioned parameters on particle motion. In this paper, we review studies particularly related to dielectrophoretic separation in microfluidic devices. Both experimental and theoretical works by several researchers are highlighted in this article covering AC and DC DEP. In addition, AC/DC DEP, which uses a combination of low frequency AC and DC voltage to manipulate bioparticles, has been discussed briefly. Contactless DEP, a variation of DC DEP in which electrodes do not come in contact with particles, has also been reviewed. Moreover, dielectrophoretic force-based field flow fractionations are featured to demonstrate the bioparticle separation in microfluidic device. In numerical front, a comprehensive review is provided starting from the most simplified effective moment Stokes-drag (EMSD) method to the most advanced interface resolved method. Unlike EMSD method, recently developed advanced numerical methods consider the size and shape of the particle in the electric and flow field calculations, and these methods provide much more accurate results than the EMSD method for microparticles.

Dielectrophoretic manipulation of erythrocytes/red blood cells is investigated as a tool to identify blood type for medical diagnostic applications. Positive blood types of the ABO typing system (A+, B+, AB+ and O+) were tested and cell responses quantified. The dielectrophoretic response of each blood type was observed in a platinum electrode microdevice, delivering a field of 0.025V(pp)/microm at 1 MHz. Responses were recorded via video microscopy for 120 s and erythrocyte positions were tabulated at 20-30 s intervals. Both vertical and horizontal motions of erythrocytes were quantified via image object recognition, object tracking in MATLAB, binning into appropriate electric field contoured regions (wedges) and statistical analysis. Cells of O+ type showed relatively attenuated response to the dielectrophoretic field and were distinguished with greater than 95% confidence from all the other three blood types. AB+ cell responses differed from A+ and B+ blood types likely because AB+ erythrocytes express both the A and B glycoforms on their membrane. This research suggests that dielectrophoresis of untreated erythrocytes beyond simple dilution depends on blood type and could be used in portable blood typing devices.

A microfluidic platform developed for quantifying the dependence of erythrocyte (red blood cell, RBC) responses by ABO-Rh blood type via direct current insulator dielectrophoresis (DC-iDEP) is presented. The PDMS DC-iDEP device utilized a 400 x 170 μm² rectangular insulating obstacle embedded in a 1.46-cm long, 200-μm wide inlet channel to create spatial non-uniformities in direct current (DC) electric field density realized by separation into four outlet channels. The DC-iDEP flow behaviors were investigated for all eight blood types (A+, A-, B+, B-, AB+, AB-, O+, O-) in the human ABO-Rh blood typing system. Three independent donors of each blood type, same donor reproducibility, different conductivity buffers (0.52-9.1 mS/cm), and DC electric fields (17.1-68.5 V/cm) were tested to investigate separation dependencies. The data analysis was conducted from image intensity profiles across inlet and outlet channels in the device. Individual channel fractions suggest that the dielectrophoretic force experienced by the cells is dependent on erythrocyte antigen expression. Two different statistical analysis methods were conducted to determine how distinguishable a single blood type was from the others. Results indicate that channel fraction distributions differ by ABO-Rh blood types suggesting that antigens present on the erythrocyte membrane polarize differently in DC-iDEP fields. Under optimized conductivity and field conditions, certain blind blood samples could be sorted with low misclassification rates.