Biorecognition-presented detection in mode-splitting-based biosensing

Abstract： A pair of counter-propagating high-Q whispering-gallery modes (WGMs) can couple to each other and produce two new standing modes with a significant resonance splitting when single or multi-scatterer are on the cavity surface. In this paper, we theoretically investigate the mode-splitting-based biosensing by using a biorecognition-covered WGM microcavity because the pre-covering is essentially necessary for label-free detection of specific biological targets. It is shown that the minimum size of biological target suitable for detection is subjected to the surface pre-covering ratio. We further propose a simple scheme for concentration detection by applying the total linewidth broadening of the two standing modes. Unlike the conventional signal by using the mode splitting itself, here the total linewidth broadening is not only immune to thermal fluctuation, but also linear with the target nanoparticle concentration in dilute solution. The relative standard error of the total broadening signal is also scrutinized.