Effects of metallic silver island films on resonance energy transfer between N , N ′‐(dipropyl)‐tetramethyl‐ indocarbocyanine (Cy3)‐ and N , N ′‐(dipropyl)‐tetramethyl‐ indodicarbocyanine (Cy5)‐labeled DNA

Resonance energy transfer (RET) is typically limited to distances below 60 Å, which can be too short for some biomedical assays. We examined a new method for increasing the RET distances by placing donor‐ and acceptor‐labeled DNA oligomers between two slides coated with metallic silver particles. A N , N ′‐(dipropyl)‐tetramethylindocarbocyanine donor and a N , N ′‐(dipropyl)‐tetramethylindodicarbocyanine acceptor were covalently bound to opposite 5′ ends of complementary 23 base pair DNA oligomers. The transfer efficiency was 25% in the absence of silver particles or if only one slide was silvered, and it increased to an average value near 64% between two silvered slides. The average value of the Forster distance increased from 58 to 77 Å. The energy transfer data were analyzed with a model assuming two populations of donor–acceptor pairs: unaffected and affected by silver island films. In an affected fraction of about 28%, the apparent energy transfer efficiency is near 87% and the Forster distance increases to 119 Å. These results suggest the use of metallic silver particles to increase the distances over which RET occurs in biomedical and biotechnology assays. © 2003 Wiley Periodicals, Inc. Biopolymers (Biospectroscopy) 70: 595–603, 2003