Ultrasonic spectroscopy of sessile droplets coupled to optomechanical sensors

TL;DR

This paper introduces an optomechanical sensor-based system for passive ultrasonic spectroscopy of tiny liquid droplets, enabling precise acoustic analysis of small biological and chemical samples within microfluidic platforms.

Contribution

The study demonstrates a novel integration of optomechanical sensors with microfluidics for passive acoustic analysis of sub-nanoliter droplets, showing excellent agreement with theoretical models.

Findings

Sensor sensitivity limited by ambient noise

Resonant features correspond to droplet breathing modes

Potential for high-precision biological and chemical sensing

Abstract

We describe a system for interrogating the acoustic properties of sub-nanoliter liquid samples within an open microfluidics platform. Sessile droplets were deposited onto integrated optomechanical sensors, which possess ambient-medium-noise-limited sensitivity and can thus passively sense the thermally driven acoustic spectrum of the droplets. The droplet acoustic breathing modes manifest as resonant features in the thermomechanical noise spectrum of the sensor, in some cases hybridized with the sensor's own vibrational modes. Excellent agreement is found between experimental observations and theoretical predictions, over the entire ~ 0 - 40 MHz operating range of our sensors. With suitable control over droplet size and morphology, this technique has the potential for precision acoustic sensing of small-volume biological and chemical samples.