FRET (Förster resonance energy transfer) is a property in which the energy of the excited electron of one fluorphore, called the donor, is passed on to a nearby acceptor dye, either a dark quencher or another fluorophore, which has an excitation spectrum which overlaps with the emission spectrum of the donor dye resulting in a reduced fluorescence.
This can be used to:
* detect if two labelled protein or nucleic acids come into contact or a doubly labelled single molecules is hydrolysed;
* detect changes in conformation;
* measure concentration by a competitive binding assay.