Nano-optomechanical disk resonators operating in liquids for sensing applications

We demonstrate that miniature optomechanical disk resonators can operate in liquids as ultrafast and ultrasensitive densimeters, viscometers and mass sensors. We develop numerical and analytical models that describe the fluid-structure interactions at play around these GHz mechanical devices. We test them experimentally by immersing disks of varying dimensions in four distinct liquids of varying density and viscosity. Using optomechanical techniques, we measure the thermomechanical noise spectrum of a disk vibrating in water at 1.3 GHz. The resonator stability measured in liquids, together with the models, allows estimating the limits of detection for mass deposition, and for density and viscosity analysis; beating current technologies by several orders of magnitude.