Trap-and-release of motile microorganisms using glass-based standing surface acoustic wave devices

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Standing surface acoustic waves (SSAWs) are an effective tool for cell manipulation and isolation in many biological and biomedical applications. Chlamydomonas reinhardtii, a unicellular motile microorganism, is an excellent biological model to study ciliary mechanics; however, its swimming strength is a challenge for trapping and analysis by conventional non-contact methods. SSAW devices incorporating polydimethylsiloxane (PDMS) channels are unable to hold C. reinhardtii due to inadequate acoustic trapping forces at power levels that do not induce excessive heating. Under operating conditions that are suitable for trapping, the sample temperature increases rapidly to exceed the thermotolerance threshold of the cells leading to loss of function or death . In this study, we show that SSAW devices with wet-etched glass channels allow for gentle trap-and-release of C. reinhardtii using 10 and 25 MHz ultrasound while traditional SSAW devices with PDMS channels kill the cells. In addition, we use infrared thermography to confirm that PDMS-based SSAW devices reach significantly higher temperatures than glass-based devices at comparable input powers. Glass-based SSAW devices easily generate the required trapping forces while maintaining a biocompatible thermal environment.