Real-time sensing of flowing nanoparticles with electro-opto-mechanics

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.