  Opto-mechano-fluidic resonators (OMFRs) are a unique optofluidics platform
that can measure the acoustic properties of fluids and bioanalytes in a
fully-contained microfluidic system. By confining light in ultra-high-Q
whispering gallery modes of OMFRs, optical forces such as radiation pressure
and electrostriction can be used to actuate and sense structural mechanical
vibrations spanning MHz to GHz frequencies. These vibrations are hybrid
fluid-shell modes that entrain any bioanalyte present inside. As a result,
bioanalytes can now reflect their acoustic properties on the optomechanical
vibrational spectrum of the device, in addition to optical property
measurements with existing optofluidics techniques. In this work, we
investigate acoustic sensing capabilities of OMFRs using computational
eigenfrequency analysis. We analyze the OMFR eigenfrequency sensitivity to bulk
fluid-phase materials as well as nanoparticles, and propose methods to extract
multiple acoustic parameters from multiple vibrational modes. The new
informational degrees-of-freedom provided by such opto-acoustic measurements
could lead to surprising new sensor applications in the near future.
