Microfluidic droplet handling by bulk acoustic wave (BAW) acoustophoresis†
Droplet microfluidics has emerged as a prospering field for lab-on-a-chip devices, where droplets serve as liquid vessels e.g. for biochemical reagents. Key to the fluid processing in droplet format are the controlled droplet handling and movement on the microscale. Hence this paper proposes droplet handling by combining droplet microfluidics with bulk acoustic wave (BAW) acoustophoresis. BAW acoustophoresis has formerly focused on cell and particle handling, whereas here we determine the various abilities of this method for the field of droplet microfluidics. In silicon microdevices, water-in-oil droplets of 200 μm size were generated for a set of unit operations including droplet fusion, focusing, sorting and medium exchange around 0.5–1 MHz acoustic frequency. Compared to existing droplet handling methods, the shown method is simple in fabrication, robust in operation and versatile to meet the needs of various droplet processing microfluidic devices.