  Mandel Q-parameter, which is determined from single event photon statistics,
provides an alternative to differentiate single-molecule with fluorescence
detection. In this work, by using the Q-parameter of the sample fluorescence
compared to that of an ideal double-molecule system with the same average
photon number, we present a novel and fast approach for identifying single
molecules based on single event photon statistics analyses, compared with
commonly used two-time correlation measurements. The error estimates for
critical values of photon statistics are also presented for single-molecule
determination.
