Selective enhancement of Raman or fluorescence spectra of biomolecules using specifically annealed thick gold films

Annealing of "thick" metal films deposited onto a smooth dielectric substrate leads to high-order self-organization of metal clusters on the film surface. This work presents the first experimental evidence that the "thick" gold film (TGF) may be specifically annealed to serve as a substrate for surface-enhanced fluorescence or surface-enhanced Raman scattering (SERS) spectroscopy of the same molecule. High-resolved SERS spectra of mitoxantrone (mitox) were recorded on the TGF annealed at 340 degrees C whereas no Raman enhancement but an increase of mitox fluorescence signal were detected on the TGF annealed at 240 degrees C. The mitox fluorescence was further enhanced by deposition of monolayers of pentanethiol or poly-L-lysine on the surface of annealed TGF. The maximal fluorescence enhancement factor per mitox molecule of approximately 50 that was obtained on the annealed TGF covered with poly-L-lysine makes the system promising for applications in immunofluorescence assays and in microspectrofluorescence analysis.