Rapid measurement of the local pressure amplitude in microchannel acoustophoresis using motile cells

TL;DR

This paper introduces a rapid, in situ method using motile algae cells to accurately measure local acoustic pressure amplitudes in microchannels, facilitating device standardization and performance monitoring in acoustofluidics.

Contribution

It extends previous qualitative mapping to a quantitative, real-time measurement technique using living microswimmers and standard microscopy, achieving high accuracy and ease of use.

Findings

Achieved agreement within 1% with conventional methods.

Enabled real-time, in situ acoustic field measurement.

Required only standard bright-field microscopy.

Abstract

Acoustic microfluidics (or acoustofluidics) provides a non-contact and label-free means to manipulate and interrogate bioparticles. Owing to their biocompatibility and precision, acoustofluidic approaches have enabled innovations in various areas of biomedical research. Future breakthroughs will rely on translation of these techniques from academic labs to clinical and industrial settings. Here, accurate characterization and standardization of device performance is crucial. Versatile, rapid, and widely accessible performance quantification is needed. We propose a field quantification method using motile Chlamydomonas reinhardtii algae cells. We previously reported qualitative mapping of acoustic fields using living microswimmers as active probes. In the present study, we extend our approach to achieve the challenging quantitative in situ measurement of the acoustic energy density. C. reinhardtii cells continuously swim in an imposed force field and dynamically redistribute as the field changes. This behavior allows accurate and complete, real-time performance monitoring, which can be easily applied and adopted within the acoustofluidics and broader microfluidics research communities. Additionally, the approach relies only on standard bright-field microscopy to assess the field under numerous conditions within minutes. We benchmark the method against conventional passive-particle tracking, achieving agreement within 1 % for field strengths from 0 to 100 J m-3 (0 to ~1 MPa).