Multiphysics optomechanical sensing of a liquid on the micron scale

We present an optomechanical device platform for characterization of rheological, optical and thermal properties of fluids on the micron scale. A suspended silicon microdisk resonator with a vibrating mass of 100 pg and an effective probing volume of less than a pL is used to monitor properties of different fluids at rest. By employing analytical models for fluid-structure interactions, thermo-optical effects and thermal diffusion, our platform determines the viscosity, density, compressibility, refractive index and thermal conductivity of the fluid, in a compact measurement setup. A single measurement takes as short as 70 μs, and the employed power can be less than 100 μW, guaranteeing measurement at rest and in thermal equilibrium.