Stretching the Förster Radius in Metal Enhanced FRET

It is well established that surface plasmon excitations can be used to enhance fluorescence in a process called Metal Enhanced Fluorescence (MEF). MEF occurs through two different mechanisms: through direct enhancement of the electromagnetic field and an increase in the local density of optical states (LDOS), the latter of which is dominant. We seek to apply MEF to Förster Resonance Energy Transfer (FRET). FRET paired molecules have a unique Förster radius (R₀), defined as the separation where there is a 50% chance of FRET occurring. We used a gold nanograting as our plasmonic substrate to extend the Förster radius.

To precisely control the distance between the FRET pair, we use DNA with a donor and acceptor molecule attached on opposite ends. These DNA sequences have different separation distances between the donor and acceptor molecules, ranging from around 1R₀ to 4R₀, where the probability of FRET occurring ranges from 50% to less than 1%. We fabricate gold nanogratings with a period of 555nm as our plasmonic substrate and spin coated a thin layer of DNA in a PVA solution onto it. This allows us to determine if effects of MEF can extend the Förster radius past what is commonly accepted, which would increase the applications of FRET to protein folding and photovoltaic cells.