Förster Resonance Energy Transfer (FRET) is a process where an excited fluorophore (donor)transfers energy to another fluorophore (acceptor) [1]. Resonance energy transfer is a distance-dependent phenomenon due to the dipole-dipole interaction between the donor and acceptormolecules.
The efficiency of the energy transfer is sensitive to the molecular distances andnegligible at distances longer than 10nm for the common fluorophores used in biologicalapplications. For this reason, when FRET is combined with fluorescence microscopy in biologicalsamples, it can be used to report molecular associations and biochemical reactions allowing themto be located precisely at the subcellular level where these processes are taking place [2].