Nonlinear electrokinetic effects in insulator‐based dielectrophoretic systems

Abstract

Insulator-based dielectrophoresis (iDEP) has emerged as a powerful tool for multiple biomicrofluidic operations, such as cell separation and concentration. The key feature for iDEP systems is the alteration of insulating microchannel geometries to create strong electric field gradients. Under AC electric fields, this strong electric field gradient can affect fluid flow by (at least) two nonlinear electrokinetic phenomena; (a) electrothermal flow due to Joule heating and (b) induced charge electroosmosis (ICEO) near the microchannel constrictions of small (but finite) permittivity and conductivity. This paper presents an experimental and theoretical study on the interplay of electrothermal and ICEO flows near microchannel constrictions with various geometries and fluid ionic strengths, which are crucial design factors for iDEP systems. Temperature rise and fluid velocities in 2D Gaussian-shaped constrictions were studied experimentally with supporting analytical estimations and numerical simulations. Additionally, we show qualitatively distinct recirculating flow patterns in 2D and 3D microchannel constrictions used for iDEP systems. Approximate analytical expressions for electrothermal and ICEO velocity scales are provided as a function of constriction geometry, bulk electrolyte concentration, and the applied electric field. Insights from this study will be useful in designing microfluidic systems for electrokinetic particle manipulation.

Recent advances in direct current electrokinetic manipulation of particles for microfluidic applications

“…Recent experiments from the author's group have reported some astonishing results (with respect to those in Newtonian fluids), such as the oscillation of particle electrophoresis in the DC electroosmotic flow of viscoelastic fluids through a constriction microchannel and the wall‐directed particle migration in the DC electroosmotic flow of shear thinning fluids through straight rectangular microchannels . Future work in this direction may cover the study of how the fluid rheological properties affect the electrokinetic motion of particles in varying microchannels, and as well the development of numerical models for understanding such motions with efficient algorithms and appropriate constitutive equations. Joule heating and induced charge effects have been usually deemed detrimental to precise electrokinetic transport and placement of particles in microchannels because of the induced electrothermal and electroosmotic flows in high‐ and low‐conductivity fluids, respectively. However, recent studies from the author's group have demonstrated the feasibility of using each of these nonlinear electrokinetic flow circulations to enrich submicron particles, which may potentially be applied to the continuous concentration of nanoparticles.…”

“…Joule heating and induced charge effects have been usually deemed detrimental to precise electrokinetic transport and placement of particles in microchannels because of the induced electrothermal and electroosmotic flows in high‐ and low‐conductivity fluids, respectively. However, recent studies from the author's group have demonstrated the feasibility of using each of these nonlinear electrokinetic flow circulations to enrich submicron particles, which may potentially be applied to the continuous concentration of nanoparticles.…”

“…Nonlinear electrokinetic phenomena refer to those electrically driven fluid flows or particle motions that depend nonlinearly on the applied electric field strength . Three types of nonlinear electrokinetic phenomena are typically involved in DC electrokinetic manipulation of particles in microchannels, which are dielectrophoretic particle motion, electrothermal fluid flow, and induced charge electroosmotic fluid flow . These phenomena are briefly reviewed below with the focus on particle DEP because the two fluid flows are usually rendered weak in electrokinetic microfluidic devices in order to minimize the adverse impacts on the samples and devices and as well ensure the accuracy in particle transport and placement .…”

Electroosmotic flow of non‐Newtonian fluids in a constriction microchannel

“…For fluid electroosmosis, iDEP devices have thus far been almost entirely restricted to work with Newtonian fluids . The insulating structures can cause electrothermal flow and/or induced charge electroosmotic flow due to the amplified Joule heating in the fluid around them and their own electrical polarization, respectively . However, many of the chemical (e.g., colloidal suspensions and polymer solutions) and biological (e.g., blood, saliva, and DNA solutions) fluids are actually complex, exhibiting non‐Newtonian characteristics .…”

High-throughput Dielectrophoretic Filtration of Sub-micron and Micro Particles in Macroscopic Porous Materials

“…Graphite particles are much more conductive and are thus experiencing positive DEP, even at much higher fluid electric conductivities than tested here. A small decrease of the separation efficiency at higher fluid conductivities is ascribed to thermal and electrothermal effects that are likely to interfere with the DEP trapping process [35], [36].…”