Enhanced emission of highly labeled DNA oligomers near silver metallic surfaces

Fluorescein is a widely used fluorescent probe in DNA analysis. One difficulty with fluorescein is its self-quenching due to resonance energy transfer between the residues, which results in decreased intensities with increasing labeling density. We examined the emission spectral properties of DNA oligomers labeled with one or five fluorescein residues. The emission intensity of the more highly labeled oligomer was decreased due to self-quenching. The self-quenching was mostly eliminated when this oligomer was held ∼90 Å from the surface of metallic silver particles. The intensities increased 7- and 19-fold for the oligomers with one or five fluoresceins, respectively. The increased intensity did not result in increased photobleaching. These results suggest the use of substrates coated with silver particles for increased sensitivity on DNA arrays or for DNA analysis.