Whispering gallery mode biosensor operated in the stimulated emission regime

Whispering gallery modes (WGMs) are generated in fluorescent polymer microparticles in phosphate buffered saline (PBS) above the threshold for stimulated emission and compared to their characteristics below threshold. The WGM microresonators show an eightfold improvement of their signal-to-noise ratio and a threefold increase in their quality factor when operated above threshold. In an investigation on the benefits for biochemical sensing, a real-time adsorption kinetics of bovine serum albumin in PBS is monitored and compared with those kinetics acquired by means of a WGM microresonator operated below threshold as well as by surface plasmon resonance (SPR).