Fluorescence correlation spectroscopy: inception, biophysical experimentations, and prospectus

Fluorescence correlation spectroscopy examines the chemical and the photoph ysical dynamics of dilute molecular solutions by measurement of the dynamic optical fluctuations of the fluorescence of a few molecules, even averagin g less than one molecule at a time, in open focal volumes that are usually less than a femtoliter (< 10(-18) m(3)). It applies the same principles of statistical thermodynamics as does quasi-elastic light scattering. Molecula r interactions, conformational changes, chemical reactions, and photophysic al dynamics that are not ordinarily detectable by quasi-elastic light scatt ering can be analyzed by fluorescence correlation spectroscopy in cases in which molecular fluorescence changes in the dynamic range 10(-7)-10(2) s. ( C) 2001 Optical Society of America.