Modeling FRET


Fluorescence Resonance Energy Transfer:


A fluorophore with an excited electron may transfer its electronic energy to another fluorophore (by resonance) if:


1.    the second fluorophore is near and

2.    the emission energy of the first molecule                              matches the excitation energy of the second.


This occurs by dipole-dipole interaction.



Dipole-dipole interaction is highly dependent upon distance. In 1948, T.M. Förster calculated that the rate of resonance energy transfer between two fluorophores would depend on the inverse of the sixth power of their separation.


Due to the sensitive dependence of FRET on inter-molecular separation, FRET has been used as an amazingly accurate “spectroscopic ruler” [Stryer, 1967].





The inverse problem for FRET:


I am interested in the ‘inverse problem’ for FRET: given FRET data, what can we know about the distances between fluorophores in the population?


For example, the inverse problem is under-determined. The location of n particles within a two-dimensional membrane has dimension 2n, whereas typical FRET observations are typically one dimensional (FRET efficiency verses some parameter of interest) or  two dimensional (FRET decay rates show flouorescence verses time and a parameter of interest).



These two configurations have the same inter-molecular differences and thus would not be distinguished with FRET.


This movie shows a simulation of the stochastic excitation of a donor (blue)  resonating with 4 potential acceptors. The excitation rate is quite high, so that there is occasional acceptor saturation.