Contributed by Daniel Daniel
Förster resonance energy transfer (FRET) is a mechanism that describes the transfer of energy between chromophores. A donor chromophore, which is in its electronically excited state, can transfer the energy non-radiatively to a acceptor chromophore that is nearby (typically less than 10 nm away) through dipole-dipole coupling. This process is known as FRET and it is exquisitely dependent on the distance between the two chromophores. FRET is often referred to as fluorescence resonance energy transfer, though this is a misnomer since the energy transfer is non-radiative and does not involve fluorescence. FRET allows imaging of objects that is separated by a distance of the order of 10 nm, which is way below the abbe diffraction limit of a microscope of 200 nm. It is one of the modern imaging techniques that allows us to surpass the diffraction limit that is characteristic of wide-field microscopy.
Figures 2 and 3 are taken from http://www.olympusfluoview.com/applications/fretintro.html