Effects of metallic silver particles on resonance energy transfer between fluorophores bound to DNA

We examined the effects of metallic silver island films on resonance energy transfer (RET) between a donor and acceptor bound to double helical DNA. The donor was 4',6-diamidino-2-phenylindole (DAPI) and the acceptor was propidium iodide (PI). Proximity of the labeled DNA to the silver particles resulted in a dramatic increase in RET as seen from the emission spectra and the donor decay times. Proximity to silver particles results in an increase of the Forster distance from 35 Angstrom to an apparent value of 166 Angstrom. These results suggest a new type of DNA hybridization assays based on RET over distances much longer than the free-space Forster distance.