Using motile cells to characterize surface acoustic wave-based acoustofluidic devices

Acoustic microfluidics is a robust and powerful method to manipulate cells and cell-like particles on chip, having good biocompatibility and ease of incorporation into multioperation microfluidic devices compared to optical manipulation. However, the use of acoustic microfluidics is largely confined to research settings. The primary barrier to translation of this technology toward clinical and industrial uses is the inability to experimentally determine the pressure field (shape and amplitude) and associated acoustophoretic forces in real time as device conditions vary. Despite the multitude of previous characterization methods, none provide the flexibility of motile cells (e.g., the unicellular alga Chlamydomonas reinhardtii) as probes to map evolving pressure fields on chip. We have previously developed this approach for use with bulk acoustic wave (BAW)-based devices. Here, we extend the method to qualitatively assess device resonances and relative field strengths for surface acoustic wave (SAW)-based devices with straight channels and circular chambers driven at 6 MHz and 20 MHz. The fabrication and electrical characterization of hybrid BAW/SAW devices with glass channels are also discussed. Upon testing, the optimal device operating parameters are identified using impedance measurements, as well as visual identification of resonant frequencies using the swimming algae cells.