Fluorescent Resonant Energy Transfer (FRET) is a process that involves two fluorochromes (molecules that have the potential to fluoresce) with overlapping emission and excitation spectra. FRET is useful in determining intra-molecular and intermolecular reactions both spatially and temporally. It can be used to follow and record the interactions of proteins, enzymes, DNA, and RNA well below the 200 nanometer (10-9 meter) resolution limit of the optical microscope at its highest magnification and with the highest numerical aperture (NA) optics. In fact, FRET
only allows resolution of interactions between 1 and 5nm, which is its beauty as well as its curse.