title: Fast single-molecule FRET spectroscopy: theory and experiment.
abstract: Single-molecule spectroscopy is widely used to study macromolecular dynamics. Although this technique provides unique information that cannot be obtained at the ensemble level, the possibility of studying fast molecular dynamics is limited by the number of photons detected per unit time (photon count rate), which is proportional to the illumination intensity. However, simply increasing the illumination intensity often does not help because of various photophysical and photochemical problems. In this Perspective, we show how to improve the dynamic range of single-molecule fluorescence spectroscopy at a given photon count rate by considering each and every photon and using a maximum likelihood method. For a photon trajectory with recorded photon colors and inter-photon times, the parameters of a model describing molecular dynamics are obtained by maximizing the appropriate likelihood function. We discuss various likelihood functions, their applicability, and the accuracy of the extracted parameters. The maximum likelihood method has been applied to analyze the experiments on fast two-state protein folding and to measure transition path times. Utilizing other information such as fluorescence lifetimes is discussed in the framework of two-dimensional FRET efficiency-lifetime histograms.
authors.affiliation: Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health (NIH), Bethesda, MD 20892-0520, USA. chunghoi@niddk.nih.gov irinag@niddk.nih.gov.
authors.forename: Hoi Sung
authors.initials: HS
authors.lastname: Chung
authors.forename: Irina V
authors.initials: IV
authors.lastname: Gopich
mesh_terms: D031541:Fluorescence Resonance Energy Transfer; D007700:Kinetics; D008962:Models, Theoretical; D056004:Molecular Dynamics Simulation; D017785:Photons; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D058767:Protein Unfolding; D011506:Proteins / Q000737:chemistry
chemical_list: D011506:Proteins
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