Particle trapping in electrically driven insulator‐based microfluidics: Dielectrophoresis and induced‐charge electrokinetics

Abstract

Electrokinetically driven insulator-based microfluidic devices represent an attractive option to manipulate particle suspensions. These devices can filtrate, concentrate, separate, or characterize micro and nanoparticles of interest. Two decades ago, inspired by electrodebased dielectrophoresis, the concept of insulator-based dielectrophoresis (iDEP) was born. In these microfluidic devices, insulating structures (i.e., posts, membranes, obstacles, or constrictions) built within the channel are used to deform the spatial distribution of an externally generated electric field. As a result, particles suspended in solution experience dielectrophoresis (DEP). Since then, it has been assumed that DEP is responsible for particle trapping in these devices, regardless of the type of voltage being applied to generate the electric field-direct current (DC) or alternating current. Recent findings challenge this assumption by demonstrating particle trapping and even particle flow reversal in devices that prevent DEP from occurring (i.e., unobstructed long straight channels stimulated with a DC voltage and featuring a uniform electric field). The theory introduced to explain those unexpected observations was then applied to conventional "DC-iDEP" devices, demonstrating better prediction accuracy than that achieved with the conventional DEP-centered theory. This contribution summarizes contributions made during the last two decades, comparing both theories to explain particle trapping and highlighting challenges to address in the near future.

High-Resolution Charge-Based Electrokinetic Separation of Almost Identical Microparticles

“…22 It is now believed that the main reason for requiring correction factors when modeling DC-iEK systems under high electric fields was that DEP effects were inaccurately considered and EP (3) effects were neglected. 7,8 This work reports the charged-based binary separation of almost identical polystyrene microparticles in an iEK device. The microparticles had the same size (5.1 μm), had the same shape, were made by the same manufacturer from the same substrate material, and had only a small difference in the particle zeta potential of 3.6 mV, which is less than 10% of the ζ P difference required by previous similar studies, which ranged from 40 to 63 mV.…”

“…Electrokinetic phenomena are classified as linear and nonlinear based on their dependence on the electric field. Many successful EK-based systems combine linear and nonlinear EK phenomena within the same device . By varying the magnitude of the applied electric potential, it is possible to shift from linear to nonlinear EK phenomena, making it straightforward to switch between EK regimes.…”

Protein Dielectrophoresis: A Tale of Two Clausius-Mossottis—Or Something Else?

“…As introduced by Cummings and Singh [86] and reviewed by its practitioners [87][88][89] the complications that electrophoresis and electroosmosis can bring to eDEP experiments, especially at frequencies below 1 kHz, are translated through iDEP into facilitators of novel microfluidic devices for the selective sorting or concentration of molecular and macroscopic bioparticles. Negative DEP manifests itself as "streaming DEP" where the particles are carried down an array of insulating posts, following stream lines dictated by the spacing and geometry of the posts and the induced electroosmotic fluid flow.…”

Microscale electrokinetic‐based analysis of intact cells and viruses

“…Until recently, DC‐insulator‐based EK (DC‐iEK) devices were called DC‐iDEP devices, since it was believed that DEP was the dominant mechanism on particle migration under the effects of electric fields. However, recent reports illustrated that this does not seem to be the case [14,93–97], that is, under DC and low‐frequency electric potentials, the nonlinear EK phenomenon of EP of the second kind is significant, and it is a major player in particle trapping [96,97]. Depending on system conditions, as described by the Peclet ( Pe ) and Dukhin ( Du ) numbers, the nonlinear EK effect of EP of the second kind is proportional to E 3/2 or E 3 [94].…”

“…Manipulation of cells with DC-iEK (formerly known as DC-iDEP [96,97]) systems is a field with numerous excellent reports, and this subsection covers some of the most recent publications. The Hayes research group has made major contributions to the biophysical characterization of cells with DC-iEK.…”