Principle and application of bubble-based oscillation for fast mixing on microfluidic chip

Mixing in microfluidic devices presents a challenge because of the laminar flow in microchannels. Here, we present an oscillatory-flow-based microfluidic mixer (OFBMM) in which fluids are subjected to a back-and-forth motion by utilizing a periodically changed pressure and an on-chip gas bubble. We developed a low-cost Arduino-based pneumatic system to apply pressure and an OpenCV-based image-processing algorithm to quantitatively analyze the mixing effect. We found that the oscillatory motion of fluids is similar to the charging and discharging process of an RC circuit used in electronics. We investigated the mixing effect by varying the oscillation frequencies, initial bubble volumes, and applied pressures. The results indicated that the increase in both the applied pressure and the initial volume of the gas bubble could promote fluid mixing. A large-scale serial dilution microfluidic chip based on OFBMM was also developed to demonstrate its biochemical potential. We believe that OFBMM will provide a new choice for mixing two or more solutions in a valves-integrated microfluidic system.