ABSTRACT
The fluorescence lifetime contains information about the photophysical processes of the fluorescent molecules and of the interactions of the fluorescent molecules with their microenvironment. Importantly, the fluorescence lifetime can be affected by the local microenvironment of the fluorescent molecule. For example, ion concentrations (pH, Ca), Förster resonance energy transfer (FRET), quenching, and conformational changes may affect the fluorescence lifetime. Consequently, the fluorescence lifetime can be used to quantify these concentrations and processes (Agronskaia, Tertoolen, and Gerritsen 2004; Bastiaens and Squire 1999; Centonze et al. 2000; Christensen 2000; Clegg 1996; Gadella, Clegg, et al. 1993; Sanders et al. 1994, 1995). Multiple lifetimes may be observed from the same detection volume due to heterogeneities in the local environment of the molecule.
