Chemical Sensing Using Optical Cavities in Microfluidic Devices

Cavity-enhanced spectroscopies are widely used for highly sensitive spectroscopic absorption measurements in the gas phase. However, they also show considerable promise as a method for enhancing detection sensitivity in measurements on small liquid volumes, such as those encountered in "lab on a chip" and chemical sensing applications. We have investigated a range of approaches to liquid-phase sensing, employing conventional "gas-phase" cavity configurations, fibre-loop cavities, and most recently, optical microcavities. The very small probed volumes coupled with the sensitivity enhancement offered by an optical microcavity allow us to detect as few as a few thousand molecules, with planned improvements offering the tantalising possibility of achieving single-molecule detection in the future.