Single-molecule nanosecond rotational diffusion analysis by time-correlated single-photon counting system

In typical photon counting single-molecule polarization-sensitive experiments, the rotational correlation time of a single fluorescent molecule is much shorter than the temporal resolution of the detection system. Consequently, a large amount of incoming photons are lost during the integration time of photon counting experiment. In order to maximize the signal-tonoise ratio for a given temporal resolution of the system, this paper suggests examining the rate of convergence and the variance of the time-averaged measured fluorescence intensity. The new suggested method is able to extract the nanosecond rotational correlation times of fluorescein dye in the different viscosities of the medium.