Analytical chemistry | 2019
High-throughput triggered merging of surfactant-stabilized droplet pairs using traveling surface acoustic waves.
Abstract
We present an acoustofluidic device for fluorescently triggered merging of surfactant-stabilized picoliter drop-let pairs at high throughput. Droplets that exceed a preset fluorescence threshold level are selectively merged by a traveling surface acoustic wave (T-SAWs) pulse. We characterize the operation of our device by analyzing the merging efficiency as a function of acoustic pulse position, duration and acoustic pressure amplitude. We probe droplet merging at different droplet rates and find that efficient merging occurs above a critical acoustic power level. Our results indicate that the efficiency of acoustically induced merging of surfactant stabilized droplets is correlated with acoustic streaming velocity. Finally, we discuss how both time-averaged and instantaneous acoustic pressure fields can affect the integrity of surfactant layers. Our technique, by allowing the merging of up to 105 droplets per hour, shows a great potential for integration into microfluidic systems for high-throughput and high-content screening applications.