Single-molecule spectroscopy inside an optical cavity

Dynamic structural changes of macromolecules undergoing biochemical reactions can be studied using a novel single pair fluorescence resonance energy transfer (sp-FRET) tool which can be used as a nanoscale spectroscopic ruler. Although recent advances in applying such a nanoscale ruler to biological systems have been made, improvements in photon detectors and photophysical properties of the single FRET pair are still being studied. Motivated by the recent progresses in single-atom laser, we have investigated the ability to use the optical microcavity to amplify the sp-FRET signal. When the single FRET pair and the attached macromolecule of interest are placed inside an optical cavity with the emission mode of the acceptor dye in resonance with the cavity mode, quantitative modeling shows that, when adjusting the acceptor-cavity coupling parameters to be appropriate values, the acceptor fluorescence emission signal amplified by the cavity coupling mode would reach a significant value, leading to a much brighter sp-FRET spectroscopic signal. Possible applications to sp-FRET measurement of biological molecules are quantitatively examined.