Effects of Metallic Silver Island Films on Resonance Energy Transfer between N,N′-(dipropyl)-Tetramethylindocarbocyanine (Cy3)- and N,N′-(dipropyl)-Tetramethylindodicarbocyanine (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)-tetramethylin-dodicarbocyanine 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.