Theoretical investigation on saturated Förster-Resonant-Energy- Transfer Microscopy using FRET dye pairs as fluorescent probes

Saturated Förster-Resonant-Energy-Transfer (FRET) microscopy (SFM) employing tiny silica nanoparticles densely co-doped with Cy3 and Cy5 molecules as fluorescent labels has been proposed and analyzed with rigorous rate equations previously, showing that optical resolutions beyond the diffraction-limit in both lateral and axial directions can be realized by exploiting the saturation effect in FRET process. Here, using a set of similar rate equations, we show that SFM can also be realized with single FRET dye pairs as fluorescent labels. A similar nonlinear optical response to excitation beam is revealed for Cy3-Cy5 dye pairs, in comparison to the silica nanoparticles co-doped with Cy3 and Cy5 molecules.