Fluorescence Resonance Energy Transfer (FRET)

Abstract

SynonymsElectronic energy transfer (EET); Förster resonance energy transfer (FRET) Definition Fluorescence resonance energy transfer (FRET) is a non-radiative, through-space excitation energy transfer process. The electronic excitation energy of a donor molecule is transferred to a ground-state acceptor through dipole-dipole interactions without involvement of a photon or molecular contact. Efficient FRET requires close proximity and suitable alignment between the transition dipoles of the donor and acceptor, as well as overlap between the donor emission spectrum and acceptor absorption spectrum. OverviewFRET was first elucidated by Theodor Förster between 1946 and 1948 [1]. Many researchers, including the International Union of Pure and Applied Chemistry (IUPAC), recognize FRET as Förster resonance energy transfer rather than fluorescence resonance energy transfer. The tribute to Förster notwithstanding, it is argued that the "fluorescence" terminology is incorrect because no photon is emitted during the energy transfer process. However, there is some value to the fluorescence resonance energy transfer terminology, which can be used to distinguish between energy transfer from optically excited donors and energy transfer from excited-state donors formed as the products of chemical or enzyme-catalyzed reactions. The latter two processes also follow the mechanism elucidated by Förster and are commonly referred to as chemiluminescence resonance energy transfer (CRET) and bioluminescence resonance energy transfer (BRET), respectively. In practice, both the "Förster" and "fluorescence" terminology are widely accepted expansions of the FRET acronym. Despite Förster's breakthrough in the mid-twentieth century, it was not until the 1990s that improvements in fluorescence instrumentation and the availability of fluorescent materials made it possible for the full potential of FRET to be realized [2]. Currently, FRET is one of the most powerful and widely utilized fluorescence techniques, with numerous applications in biology, biochemistry, biophysics, and bioanalysis.Physically, the FRET process is summarized in Eq. 1, where D represents the donor fluorophore, A represents the acceptor chromophore, and * indicates an excited electronic state.