Acoustic valves in microfluidic channels for droplet manipulation.

A novel concept of using acoustic valves in microfluidic channels is reported in this work for the first time. An acoustic valve is a controllable virtual barrier constructed with focused acoustic fields, which can control droplets into different branch channels or block and then release them to specific target channels. Compared with other droplet sorting devices using a surface acoustic wave, acoustic valves do not use an acoustic field to drive droplets but only block branch channels. Compared with other sorting methods, such as using dielectric and magnetic forces, acoustic valves do not need a high voltage or target sample modification. As a non-contact and low-damage manipulation method with minimal requirements for target samples, the use of acoustic valve is suitable for microfluidic applications like sorting and manipulation in biochemical experiments, especially those involving optical observation, fluorescence testing, and chemical reactions.