Multidimensional droplet manipulation on superhydrophobic surfaces using acoustic tweezers

Abstract

On-demand droplet manipulation plays a critical role in microfluidics, bio/chemical detection and micro-reactions. Acoustic droplet manipulation has emerged as a promising technique due to its non-contact nature, biocompatibility and precision, circumventing the complexities associated with other methods requiring surface or droplet pretreatment. Despite their promise, existing methods for acoustic droplet manipulation often involve complex hardware setups and difficulty for controlling individual droplet amidst multiple ones. Here we fabricate simple yet effective acoustic tweezers for in-surface and out-of-surface droplet manipulation. It is found that droplets can be transported on the superhydrophobic surfaces when the acoustic radiation force surpasses the friction force. Using a two-axis acoustic tweezer, droplets can be maneuvered along arbitrarily programmed paths on the surfaces. By introducing multiple labyrinthine structures on the superhydrophobic surface, individual droplet manipulation is realized by constraining the unselected droplets in the labyrinthine structures. In addition, a three-axis acoustic tweezer is developed for manipulating droplets in three-dimensional space. Potential applications of the acoustic tweezers for micro-reaction, bio-assay and chemical analysis are also demonstrated.