Fluorescence lifetime imaging microscopy: spatial resolution of biochemical processes in the cell.

Fluorescence lifetime imaging microscopy (FLIM) is a technique in which the mean fluorescence lifetime of a chromophore is measured at each spatially resolvable element of a microscope image. The nanosecond excited-state lifetime is independent of probe concentration or light path length but dependent upon excited-state reactions such as fluorescence resonance energy transfer (FRET). These properties of fluorescence lifetimes allow exploration of the molecular environment of labelled macromolecules in the interior of cells. Imaging of fluorescence lifetimes enables biochemical reactions to be followed at each microscopically resolvable location within the cell.