Predicting the retention time of microparticles in electrokinetic migration†

Abstract

Insulator based electrokinetic (iEK) devices have emerged as powerful tools for analyzing both nano- and microparticles due to their simplicity, robustness, and ability to integrate linear and nonlinear electrokinetic (EK) effects into a single platform. Recent studies emphasize the importance of nonlinear electrophoresis (EP_NL) in particle analysis, for performing separations based on size, shape, and charge differences. Despite these advancements, the development of an empirical equation for predicting particle retention times in iEK-based systems that incorporates EP_NL remains limited. This study presents a method for predicting particle retention time in iEK systems in scenarios where the linear EK regime allows for particles migration, while also incorporating EP_NL and accounting for particle characteristics, applied electric fields, and microdevice features. Experiments were conducted using eight reference microparticles, grouped into four pairs with similar sizes (3.6 μm to 11.7 μm) but distinct zeta potentials (∼−20 mV and ∼−30 mV), across three distinct iEK microdevices: one with asymmetrical oval-diamond posts, one with symmetrical oval posts, and one postless design. Experimental retention times (t_R,e) were measured at applied voltages ranging from 400 V to 1450 V. Using the collected t_R,e data, three empirical equations were developed to describe particle velocity, incorporating both linear and nonlinear velocities. Validation with two control particles demonstrated prediction errors below 24% in all devices. These findings underscore the potential of the empirical equations in predicting particle behavior in iEK systems.