Optomechanical Density Sensor for Sample Consumption of Dozens of Nano-Liters Based on Microbubble Microcavity

Benefiting from the bridgework between cavity optomechanics and optofluidics, microbubble resonators (MBRs) have attracted wide attention both in optomechanics sensing and fundamental research. In this work, we present a novel approach for achieving a fluid mass density sensor based on optomechanics in MBRs. The density responsivity can range from -1.27~-1.54 MHz/(g/ml) for 4 types of mechanical modes. The validation of responsivity is analyzed theoretically, and the calculations indicate that a shorter average radius of the shell can achieve higher responsivity. The density responsivity in a smaller sized and thicker MBR can reach -2.147 MHz/(g/ml). Due to the small volume of the MBRs, the sample consumption can be controlled to dozens of nano-liters, which can greatly reduce the cost of sensing expensive biological samples.