Back-scatter based whispering gallery mode sensing

TL;DR

This paper introduces a back-scatter detection method for whispering gallery mode sensors that significantly reduces noise, enabling highly sensitive detection of single molecules and advancing biosensing capabilities.

Contribution

The paper presents a novel back-scatter detection technique that suppresses frequency and thermorefractive noise, improving sensitivity in whispering gallery mode biosensors.

Findings

Achieved 27 dB frequency noise suppression.

Demonstrated absolute frequency shift sensitivity of 76 kHz.

Enabled potential for single molecule biophysics experiments.

Abstract

Whispering gallery mode biosensors allow selective unlabelled detection of single proteins and, combined with quantum limited sensitivity, the possibility for noninvasive realtime observation of motor molecule motion. However, to date technical noise sources, most particularly low frequency laser noise, have constrained such applications. Here we introduce a new technique for whispering gallery mode sensing based on direct detection of back-scattered light. This experimentally straightforward technique is immune to frequency noise in principle, and further, acts to suppress thermorefractive noise. We demonstrate 27 dB of frequency noise suppression, eliminating frequency noise as a source of sensitivity degradation and allowing an absolute frequency shift sensitivity of 76 kHz. Our results open a new pathway towards single molecule biophysics experiments and ultrasensitive biosensors.