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

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 Rs = 0.5 to a final resolution Rs = 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.