  High-throughput label-free measurements of the optical and mechanical
properties of single microparticles play an important role in biological
research, drug development, and related large population assays. Mechanical
detection techniques that rely on the density contrast of a particle with
respect to its environment are blind to neutrally bouyant particles. However,
neutrally buoyant particles may still have a high compressibility contrast with
respect to their environment, opening a window to detection. Here we present a
label-free high-throughput approach for measuring the compressibility (bulk
modulus) of freely flowing microparticles by means of resonant measurements in
an opto-mechano-fluidic resonator.
