Orientational Dependence of Metal Enhanced Fluorescence Between Bound FRET Molecules

The availability of surface plasmon excitations have been shown to increase the efficiency of Förster resonance energy transfer (FRET) near a substrate through a process called metal enhanced fluorescence (MEF). These excitations are determined by properties of the plasmonic substrate, whether it be a nano-patterned surface or nanoparticle. Enhancement of FRET can be observed as an increase in FRET efficiency, the probability of energy transfer from the donor to acceptor molecule. The efficiency of FRET is proportional to both the Förster Radius (R₀), the radius at which efficiency is 50 percent, as well as the relative orientation of the fluorescent molecules’ transition dipoles. Many studies neglect to account for the relative orientations of fluorescent molecules’ transition dipoles when probing the increase of FRET efficiency using plasmonic systems. We use DNA as a spacer to separate FRET pairs and vary their relative orientations. By placing these bound FRET pairs near a plasmonic substrate with tunable plasmon wavelengths, we can determine if the relative dipole orientation has an effect on MEF. Any enhancement of FRET would increase the distances at which FRET could be used as a probe and thus increase the applicability of FRET.