Fluorescence resonance energy transfer
Fluorescence resonance energy transfer (FRET) is a molecular visualization technique where two chromaphores, 2-8 nm apart, transfer energy between each other in a measurable way. The distance between the markers can be accurately calculated from the amount of energy emitted.
Intramolecular FRET has been used to measure the distance between parts of a protein, helping to illuminate the structure. Intermolecular FRET has been used to study ligand-receptor interaction.