Optomechanical crystals for spatial sensing of submicron sized analytes

TL;DR

This paper demonstrates an optomechanical crystal cavity sensor capable of detecting and analyzing submicrometer biological particles by monitoring frequency shifts in specific mechanical modes under ambient conditions.

Contribution

It introduces a novel design of an optomechanical crystal cavity that uses low modal-volume modes for sensitive detection of analytes based on frequency shifts.

Findings

Successfully detects submicrometer particles via frequency shifts.

Designs cavity modes that are insensitive to perturbations elsewhere.

Provides a method to estimate particle position and quantity.

Abstract

Optomechanical crystal cavities have rich perspectives for detecting and indirectly analysing biological particles, such as proteins, bacteria and viruses. In this work we demonstrate the working principle of an optomechanical crystal cavity operating under ambient conditions as a sensor of submicrometer analytes by optically monitoring the frequency shift of thermally activated mechanical modes. The resonator has been specifically designed so that the cavity region supports a particular family of low modal-volume mechanical modes, commonly known as -pinch modes-. These involve the oscillation of only a couple of adjacent cavity cells that are relatively insensitive to perturbations in other parts of the resonator. The eigenfrequency of these modes decreases as the deformation is localized closer to the centre of the resonator. Thus, by identifying specific modes that undergo a frequency shift that amply exceeds the mechanical linewidth, it is possible to infer if there are particles deposited on the resonator, how many are there and their approximate position within the cavity region.