Förster Resonance Energy Transfer

FRET http://photobiology.info/PDF/History%20of%20FRET.pdf https://link.springer.com/article/10.1140%2Fepjh%2Fe2013-40007-9

by Dr. B. Wieb VanDerMeer, Department of Physics and Astronomy, Western Kentucky University, Bowling Green, KY 42101-1077, USA.

FRET is Fluorescence with Resonance Energy Transfer, or Fluorescence-detected Resonance Energy Transfer, or Förster Resonance Energy Transfer. It is an absorption of electromagnetic radiation by one molecule, the “donor,” followed by resonance interaction with another molecule, the “acceptor.” As a result, energy is transferred from donor to acceptor. The two molecules can be different or identical. If the two molecules are different, the process is called “hetero-transfer” (illustrated in Figure 1). If the two are identical we speak of “homo-transfer” (illustrated in Figure 2) and the energy can go back and forth for a while or go to yet another molecule until emission or a radiation-less transition takes place. FRET is extremely sensitive to the distance between the interacting molecules and can be used to visualize interactions and to measure distances between 1 and 10 nanometers.

Figure 1. Schematic representation of the various processes taking place during hetero-transfer. In (a) a photon with frequency matching the excitation spectrum of a donor (“photon-in”) and a donor are shown just before excitation, (b) after the photon is absorbed the donor is in an excited state and two possible pathways are available. If the separation distance, [math]r_{DA}[/math], is bigger than the Förster distance, [math]R_{0}[/math], the pathway (c)-to-(d) is dominant: the donor stays excited for a few nanosecond (c), and then, (d), emits a fluorescent photon (“photon-out”). If [math]r_{DA}[/math] is smaller than [math]R_{0}[/math], the pathway (e)-to-(f) is dominant. The donor will resonate with an acceptor (e). FRET takes place and energy is transferred to the acceptor (f). If the acceptor is fluorescent the acceptor may emit (sensitized emission, not shown).