Precisely controlled microdroplet merging by giant-electrorheological-fluid-based microvalve

Abstract

A microfluidic device with a microvalve incorporated with intelligent giant electrorheological fluid (GERF) was proposed to actively and accurately control micro-droplet merging in various droplet scales. The GERF is a suspension without an additional electric field, and its viscosity can be increased with the increase in the voltage. A chamber composed of an expanded channel with thin membranes on both sides and several pillars is used to realize droplet merging. The chamber can restrict droplet flow to ensure droplet contact. When the pressure is applied by the microvalve, the membranes would pump up to the merging chamber. Thus, the pressure difference between the merging chamber and GERF channel could be controlled by the membranes’ deformation and influence the merging of the droplets. Therefore, the number of merged droplets from zero to five can be controlled when the flow rate of both the continuous phase and the discrete phase was 0.5 µl/min or from four to zero when the flow rate of the continuous phase was 0.8 µl/min and the discrete phase was 0.2 µl/min. The micro-chip can be easily fabricated without complex equipment, and only a pair of electrodes are required to control the microvalve. Thus, the proposed device has excellent application prospects in chemical synthesis and single-cell analysis.