Probing single-molecule dynamics photon by photon

We present the theoretical rationales for data analysis protocols that afford an efficient extraction of conformational dynamics on a broad range of time scales from single-molecule fluorescence lifetime trajectories. Based on correlation analyses, a photon-by-photon approach on one hand provides the highest time resolution, whereas a minimal-binning method on the other hand is most suitable for experiments experiencing external fluorescence intensity variations. Applications of the two methods are illustrated via computer simulations. In cases where fluorescence quenching is either due to Förster fluorescence resonance energy transfer or due to the excited-state electron transfer, the fluorescence lifetime is dependent on donor-acceptor distance, thereby providing a window through which conformational dynamics are revealed. To assist in interpreting experimental data derived from the new protocols, analytical expressions relating fluorescence lifetime fluctuation correlations to a Brownian diffusion model and to an anomalous diffusion model are discussed. © 2002 American Institute of Physics. @DOI: 10.1063/1.1521154#