Low- and High-Frequency Characterization of Hybrid Acoustofluidic Devices Using Motile Cells

Acoustic microfluidics has become a powerful and robust tool for non-contact, label-free, and biocompatible manipulation of microscale bioparticles. However, current technologies are mostly confined to specialized research laboratories. Low operational consistency and repeatability are key barriers that impede realization of commercially viable platforms. Industrial and clinical applications also require real-world performance monitoring. Thus, there is an urgent need for rapid and precise methods to experimentally characterize acoustofluidic devices. We propose to use the unicellular alga Chlamydomonas reinhardtii to assess the acoustic field within a hybrid acoustic microfluidic platform. Unlike the passive particles typically used for such measurements, C. reinhardtii cells swim freely and redistribute in the absence of a strong acoustic field, which allows a population of cells to represent a continuously changing acoustic pressure distribution. We use this method to characterize novel hybrid acoustofluidic devices that incorporate bulk acoustic waves generated by mode conversion of surface acoustic waves. Optimal low and high resonant frequencies of operation are identified, and acoustic pressure fields are imaged in real-time using the distribution density of C. reinhardtii cells. Measurements confirm the high energy transfer efficiency of these hybrid devices, which are suitable for biocompatible trapping of microswimmers and other difficult-to-manipulate particles.