Fluorescence Resonance Energy Transfer (FRET) has long been known to be a smart method for visualization of molecular interactions of proteins and nucleic acids. The discovery and development of the Fluorescent Proteins as CFP or YFP have led to an increased use in microplate assays.

FRET is based on the fact, that a donor dye (e.g. CFP) in an excited state can transfer a part of its energy to an acceptor molecule like YFP. The emission from the acceptor can be detected as soon as both dyes are in close proximity when e.g. interaction of two proteins has taken place.

FRET is used analytically for many assays where

• the structure of a macromolecule changes
• the binding of a ligand to a macromolecule is of interest

FRET assays can be performed easily by using the multimode readers Mithras LB 940 or TriStar LB 941 and the fluorometer Twinkle LB 970 supporting fast filter changes and double emission measurements.