On the heating and patterning dynamics in acoustic tweezers based on surface acoustic waves*

Acoustic tweezers enable a non-invasive, label- and contact-free method for the precise manipulation of micro objects, which is of particular importance for biological cells to avoid (cross-)contamination and to prevent cell death. Although, cells are subjected to mechanical and thermal stress, acoustic tweezers are usually considered as biocompatible. In this presentation, the correlation between acoustic fields and acoustophoretic motion of particles as well as heating effects caused by inherent energy conversion processes are revealed, applying laser Doppler vibrometry, astigmatism particle tracking velocimetry and luminescence lifetime imaging in parallel. In situ measurements with high spatial and temporal resolution reveal not only a 3D particle patterning coinciding with the experimentally assisted numerical result of the acoustic radiation force distribution, but also a significant and very rapid temperature rise of up to 55°C depending on acoustic power and position of the particles within the microfluidic chamber. Besides, while particle patterning establishes within less than 2 seconds, temperature rises within a few tens of seconds.