We propose a novel continuous-flow microfluidic particle concentrator with a specified focusing-particle number ratio (FR) at different channel outlets using induced-charge electroosmosis (ICEO). The particle-focusing region contains two floating electrodes of asymmetric widths L₂ and L₁ in the gap between a driving electrode pair, all of which are fabricated in parallel in the main channel. Applying an AC voltage over the driving electrodes, an ICEO flow with two vortexes can be induced over each of the two floating electrodes, and the actuation range of the ICEO vortex is proportional to the respective electrode size. We establish a preliminary physical model for the value of FR: at a moderate voltage and frequency range, FR approaches L₂/L₁ due to the scaled ICEO actuation range; by further modifying the voltage or frequency, FR is freely adjustable because of the variation in ICEO velocity. Furthermore, by connecting multiple focusing regions in series, i.e., high FR = (L₂/L₁)ⁿ can be conveniently generated in an n-stage flow focusing device. Our results provide a promising method for yielding transverse concentration gradients of particles useful in pre-processing before analysis.

In this work, we proposed a novel design of a microfluidic mixer utilizing the amplified Marangoni chaotic advection induced by alternating current (AC) continuous electrowetting of a metal droplet situated in electrolyte solution, due to the linear and quadratic voltage-dependence of flow velocity at small or large voltages, respectively. Unlike previous researchers exploiting the unidirectional surface stress with direct current (DC) bias at droplet/medium interface for pumping of electrolytes where the resulting flow rate is linearly proportional to the field intensity, dominance of another kind of dipolar flow pattern caused by local Marangoni stress at the drop surface in a sufficiently intense AC electric field is demonstrated by both theoretical analysis and experimental observation, which exhibits a quadratic growth trend as a function of the applied voltage. The dipolar shear stress merely appears at larger voltages and greatly enhances the mixing performance by inducing chaotic advection between the neighboring laminar flow. The mixer design developed herein, on the basis of amplified Marangoni chaotic advection around a liquid metal droplet at larger AC voltages, has great potential for chemical reaction and microelectromechanical systems (MEMS) actuator applications because of generating high-throughput and excellent mixing performance at the same time.