Acoustically Activated Nozzle for Microdroplet Generation and Dispensing

Droplet-based microfluidic has emerged as a versatile tool for widespread applications, such as biochemical analysis and synthesis, for which the generation and manipulation of the microdroplets are fundamental. Acoustic based droplet control has shown advantages of good biocompatibility and widescale tunability. Here, we demonstrate an acoustic controlled nozzle that is integrated with both generation and directed dispensing of microdroplets. The system can generate monodisperse microdroplets with tunable sizes (50--641 \textmu{}m) at a highest throughput of 2000 droplets per second. Besides, by tuning the acoustic frequency, the droplets can be steered to different directions after their formation, realizing on-demand dispensing of the microdroplets. The controlled microdroplet generation and dispensing are both attributed to the acoustic streaming effect induced by the nozzle vibration. Two basic mechanisms for the droplet control were studied: (1) the correlation between the droplet size and the acoustic actuation time, (2) the dependence of the droplet dispensing direction on the acoustic frequency. This work paves the way towards programmable control over acoustic generation and dispensing of microdroplets, which has great potential in the applications of bio-chemical analysis and synthesis.