Living probes as calibration standards for acoustic microfluidics

Abstract

Acoustic microfluidics is promoted as an enabling technology for numerous applications in medicine and biology; however, adoption of these solutions in clinical and industrial settings is hampered by inconsistent performance and poor reproducibility. Though computational modeling and laboratory-scale demonstrations anticipate significant advantages for acoustofluidic unit operations including mixing, sorting/separation, and isolation, few technologies have realized this potential. A lack of standard tools and methods for assessing and comparing device performance represents a critical barrier to progress in the field. Here, we introduce a living probe that allows accurate and dynamically responsive measurement of the acoustic pressure within a device. Motile unicellular alga Chlamydomonas reinhardtii (CR) probe their environment and naturally swim against an imposed force field to fill complicated shapes. Steady-state distributions of swimming cells can be related to the field shape and strength to more completely describe the pressure field (versus passive particles that reach terminal distributions at nodal locations). Significantly, CR cells continuously respond to their environment, which enables real-time observation of the system response to varying operating conditions (e.g., frequency and/or drive voltage). We present the results that demonstrate correlation of CR cell distributions with pressure fields in simple one- and two-dimensional shapes, as well as more complex architectures.