On-chip acoustic mixer integration of electro-microfluidics towards in-situ and efficient mixing in droplets

Rapid and reliable micromixing requires continuous improvement to renovate more powerful microfluidics chip for chemosynthesis, biological assay, and drug purification. In this work, we realized rapid in-situ mixing in droplets on a closed electro-microfluidic chip. Electrowetting and 2.5 GHz acoustic wave streaming were coupled into a monolithic chip for the manipulation and active mixing of microdroplets, respectively. Finite-element analysis simulation provided three-dimensional illustrations of turbulent flow pattern, fluid velocity, and vortices core locations. We carried out mixing experiments on different scales from nanoscale molecules to microscale particles, accelerating mixing efficiency by more than 50 times compared with pure diffusion. In the enzyme catalytic reaction experiment for biological assay demonstration, mixing efficiency of biological samples improves by about one order of magnitude compared with conventional 96-well-plate assay. Limited temperature rising of mixing in microdroplets validates biological safety, which guarantees potentials of the chip in various biochemical analyses and medical applications.