Förster Resonance Energy Transfer (FRET)

An excited fluorophore (donor) can transfer its energy to another fluorophore in close proximity (acceptor) by dipole-dipole interactions. This process is referred to as either Fluorescence resonance energy transfer or Förster resonance energy transfer (FRET).

The rate of energy transfer (kFRET) depends strongly on the distance between the donor and the acceptor. The near field of the donor decays proportional to the third power of the distance. The transition dipole of the acceptor is induced by the donor near field, resulting in a dependence of kFRET on the square of the donor field and thus on the sixth power of the donor-acceptor separation R.

Thus FRET can be used as a ruler at bio-molecular level to measure inter-molecular and intra-molecular distances.

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