Figure 4.

Diagrammatic representation of FRET. FRET describes an energy transfer mechanism between two chromophores. A donor chromophore in its excited state can transfer energy to an acceptor chromophore in close proximity (typically <10 nm). For monitoring the complex formation between two molecules, one of them is labeled with a donor and the other with an acceptor, and these fluorophore-labeled molecules are mixed. When they are dissociated, the donor emission is detected upon the donor excitation. On the other hand, when the donor and acceptor are closer (<10 nm), the acceptor takes the energy from the donor and emit photons of different color.