Enhancing detection limit of whispering gallery mode microcavity for intracellular sensing applications

We demonstrate that incorporating Förster resonant energy transferring (FRET) mechanism to the Whispering gallery mode (WGM) microcavity can greatly enhance the sensitivity. A donor-dye doped microsphere is embedded in an acceptor dye solution, which forms a FRET-WGM sensing platform. Pumping the WGM microcavity with a pulsed laser, we obtained simultaneous lasing of donor and acceptor dyes. The gap between donor and acceptor resonant wavelengths serves as a readout for acceptor quantification. Compared with the pure WGMs sensing system, the detection limit of FRET-WGM is greatly decreased, which enables us to realize real-time monitoring and quantitative analysis of intracellular fluorescent substance at single cell level.