Investigation of the impact of liquid presence on the acoustic streaming generated by a vibrating sharp tip capillary

Sharp edge structures have been demonstrated as an efficient way of generating acoustic streaming in microfluidic devices, which finds numerous applications in fluid mixing, pumping, particle actuation, and cell lysis. A sharp tip capillary is widely available means of generating sharp structures without the need of microfabrication, which has been used for studying enzyme kinetics, droplet digital PCR, and mass spectrometry analysis. In this work, we studied the influence of liquid inside the vibrating glass capillary on its efficiency of generating acoustic streaming. Using fluorescence microscopy and fluorescent particles, we observed that adding liquid to the inside of the vibrating glass capillary changed the streaming patterns as well as led to increased streaming velocity. Based on the observed streaming patterns, we hypothesized the liquid present in the capillary changed vibration mode of the capillary, which is matched with COMSOL simulations. Finally, the utility of the liquid filled vibrating capillary was demonstrated for higher energy efficiency for fluid mixing and mass spectrometry experiments. This study will provide useful guidance when optimizing the efficiency of vibrating sharp tip capillary systems.