  High-Q optical resonators allow label-free detection of individual
nanoparticles through perturbation of optical signatures but have practical
limitations due to reliance on random diffusion to deliver particles to the
sensing region. We have recently developed microfluidic optomechanical
resonators that allow detection of free-flowing particles in fluid media with
near perfect detection efficiency, without requiring labeling, binding, or
direct access to the optical mode. Rapid detection of single particles is
achieved through a long-range optomechanical interaction that influences the
scattered light spectra from the resonator, which can be quantified with
post-processing. Here, we present a hybrid electromechanical-optomechanical
technique for substantially increasing the bandwidth of these
optomechanofluidic sensors, enabling real-time operation. The presented system
demonstrates temporal resolution of better than 20~\us (50,000 events/second)
with particle sensing resolution down to 490 nm, operating in the air without
any stabilization or environmental control. Our technique significantly
enhances the sensing capabilities of high-Q optical resonators into the
mechanics domain, and allows extremely high-throughput analysis of large
nanoparticle populations.
