Controlling Fret Enhancement Using Plasmon Modes On Gold Nanogratings

The optical properties of structured metal surfaces and nanoparticles can be engineered to influence the fluorescence properties of nearby quantum emitters through the manipulation of the local density of optical states (LDOS). Applying these techniques to Forster resonance energy transfer (FRET) is appealing but has proven to be a complicated and debated issue. In this paper, surface plasmons modes for a gold nanograting are found to enhance the FRET efficiency between nearby donor and acceptor molecules. Nanogratings support traveling surface plasmon waves with a broad range of wavelengths that follow a dispersion relationship, allowing for increases in the LDOS at targeted portions of the spectra of FRET paired molecules. Nearby excited fluorescent molecules may decay by launching a surface plasmon wave that couples into free-space light, which can be recovered. With this system, we measured the FRET efficiency for different plasmon wavelengths spanning both the donor and acceptor emission spectra. The increase in efficiency was found to be greatest when the surface plasmon modes, and therefore the increase in LDOS, overlapped the acceptor emission spectrum.