Fine-Tuning the Characteristic of the Applied Potential To Improve AC-iEK Separations of Microparticles

Abstract

There is an immediate need for the development of rapid and reliable methods for microparticle and cell assessments, and electrokinetic (EK) phenomena can be exploited to meet that need in a low cost and label-free fashion. The present study combines modeling and experimentation to separate a binary mixture of microparticles of the same size (5.1 μm), shape (spherical), and substrate material (polystyrene), but with a difference in particle zeta potentials of only ∼14 mV, by applying direct current (DC)-biased low-frequency alternating current (AC) voltages in an insulator-based-EK (iEK) system. Four distinct separations were carried out to systematically study the effect of fine-tuning each of the three main characteristics of the applied voltage: frequency, amplitude, and DC bias. The results indicate that fine-tuning each parameter improved the separation from an initial separation resolution R s = 0.5 to a final resolution R s = 3.1 of the fully fine-tuned separation. The separation method exhibited fair reproducibility in retention time with variations ranging from 6 to 26% between experimental repetitions. The present study demonstrates the potential to extend the limits of iEK systems coupled with carefully fine-tuned DC-biased low-frequency AC voltages to perform discriminatory micron-sized particle separations.

Development of a DC-Biased AC-Stimulated Microfluidic Device for the Electrokinetic Separation of Bacterial and Yeast Cells

“…Potential causes of the observed deviations between the modeled and experimental results include local electric field distortions caused by cells, cell interactions, and EK injection bias during sample injection [60,64], since these effects are currently not included in the model. These results leveraged the findings from two previous reports on fine-tuning the characteristics of the applied AC potential [48] and iEK device [49]. The findings of this study extended the limits of DC-biased AC-iEK systems to separate spherical and non-spherical cell mixtures with complexities ranging from cells from different domains to cells from the same species.…”

“…The present study leverages previous reports focused on fine-tuning the characteristics of the applied AC potential [48] and iEK device [49], respectively. Presented here is the application of this new knowledge for the separation of three distinct biological samples.…”

“…The Xuan group demonstrated this by focusing of yeast cells in a serpentine microchannel [46], and in a virtually "infinite" microchannel [47], by employing low-frequency AC voltages. Our group investigated the effects of fine-tuning DC-biased AC potentials and manipulating the insulating post array on microparticle separation [48,49] and compared the separation of E. coli and Saccharomyces cerevisiae (S. cerevisiae) cells using DC-biased low-frequency AC signals [50]. We reported that the application of DC-biased AC potentials had an added advantage in comparison with DC signals [50] when applied to iEK systems.…”

Particle Size-Dependent Electrophoresis in Polymer Solutions

“…Electrophoresis is the movement of a charged particle with respect to a liquid electrolyte under an applied electric field. , It has found many applications, ranging from DNA sequencing by capillary electrophoresis to cell manipulation in electrokinetic microfluidic devices. − The electrophoretic velocity of a moderately charged particle with σ* = σ a /εϕ ∼ 1, where σ is the particle’s surface charge density, a is the particle radius, ε is the liquid permittivity, and ϕ is the thermal voltage, is a linear function of the imposed electric field strength, E , when β = Ea /ϕ ≪ 1. , This velocity follows Henry’s formula and exhibits an explicit dependence on the particle size through δ = 1/κ a , with 1/κ being the Debye length. , It reduces to Smoluchowski’s formula under the thin-Debye-layer limit with δ ≪ 1, which becomes independent of the particle size and shape . This regime of linear electrophoresis, however, breaks down for a highly charged particle with σ* ≫ 1 and/or under a large electric field with β ≫ 1 because of the surface conduction effect in the Debye layer. − The resulting nonlinear contribution to the electrophoretic velocity has been demonstrated to depend on the size, charge, and shape of the particle. − Particle size-dependent electrophoretic velocity (more accurately, electrokinetic velocity because of the contribution of fluid electroosmosis) also occurs in a confined microchannel because of the boundary effect. , This dependence, however, remains insignificant unless the particle size-to-channel width ratio reaches the order of unity. , …”

On the behavior of sub‐micrometer polystyrene particles subjected to AC insulator‐based dielectrophoresis

“…An alternative to DC‐iDEP is practiced by a few research groups, where AC conditions are applied in insulator‐based geometries [9, 10, 30–41]. Electroosmosis and EP can be suppressed for sufficiently large frequencies in AC‐iDEP, typically above 1 kHz [29].…”