Metal-enhanced fluorescence of conjugated polyelectrolytes with self-assembled silver nanoparticle platforms.

We report the use of a simple Ag nanoparticle (NP) platform to enhance the fluorescence signatures of conjugated polyelectrolytes (CPEs). Ag NP platforms with different extinction intensities were fabricated by self-assembly of Ag NPs on NH(3)(+)-functionalized glass surface. Layer-by-layer (LBL) deposition of oppositely charged polyelectrolytes is used to control the Ag NP-CPE distance. The Ag NP platforms with high optical densities provide higher fluorescence enhancement factors for CPEs as compared to those with low optical densities. In addition, the CPE fluorescence enhancement is found to be directly related to the overlap between the absorption spectra of CPEs and the extinction spectra of Ag NP platforms. Both steady-state and time-resolved fluorescence spectroscopic studies reveal that the fluorescence enhancement is controlled by the increase in both absorption and radiative decay rates of the CPEs in proximity of Ag NPs. The enhanced CPE fluorescence signature is further used to detect single-stranded DNA using a Cy5 dye labeled peptide nucleic acid probe (Cy5-PNA) through Förster resonance energy transfer (FRET). We anticipate that the organic-inorganic hybrid platform will provide new opportunities for CPE application in sensing and device fabrication.