F örster Resonance Energy Transfer and Fluorescence Lifetime Imaging

One of the most useful properties of the fluorescence lifetime is that it offers a view on the decay kinetics of fluorescent probes. This can be used to detect and quantify a highly useful and popular photophysical phenomenon among the life scientists: Forster resonance energy transfer (FRET), the relocation of energy from the excited state of one fluorophore to a suitable acceptor fluorophore. Fluorescence lifetime imaging microscopy (FLIM) measures the average duration of the excited state, that is, the fluorescence lifetime 𝜏. This chapter outlines the origins, consequences, measurements, and implications of FRET in the life sciences. The extreme distance dependence of FRET between fluorophores, correctly described for the first time by Theodor Forster, provides an important tool for the determination of molecular-scale interactions and structural rearrangements of biomolecules. The chapter deals with the different methods for detecting FRET.