FRET (Fluorescence Resonance Energy Transfer) is the non-radiative transfer of energy from an excited fluorophore (donor) to another fluorophore (acceptor). FRET only occurs when the molecules concerned are in very close proximity (1-10 nm). This makes it a valuable technique for studying interactions between molecules. Exciting the donor and then monitoring the relative donor and acceptor emissions, either sequentially or simultaneously makes it possible to determine when FRET has occurred.
FRET can then be used to determine when and where two or more biomolecules, often proteins, interact. Energy transfer occurs over distances of 1-10 nm which means that determining distance between interacting proteins can be made more accurate than the optical resolution (~0.25 mm) of the light microscope. This is a useful tool to quantify molecular dynamics in biophysics and biochemistry, such as protein-protein interactions, protein-DNA interactions, and protein conformational changes.
Fluorophores
A common combination of fluorophores is cyan fluorescent protein (CFP) and yellow fluorescent protein (YFP), a donor-acceptor pair is used for studying protein-protein interactions in cells of interest.
When CFP is excited and the two molecules are within 10 nm of each other, energy may be transferred from the excited CFP to the YFP causing the YFP to emit yellow light, which is then detected independently of the blue light that excited CFP.
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Fluorescence Resonance Energy Transfer (FRET)