Fluorescence and Fourier Transform Surface-Enhanced Raman Scattering Measurements of Methylene Blue Adsorbed onto a Sulfur-Modified Gold Electrode

Surface enhanced Raman scattering (SERS) and molecular fluorescence are used to probe the structure of a methylene blue monolayer adsorbed onto a sulfur-modified polycrystalline gold electrode. Changes in the wavelength of fluorescence for methylene blue on the gold electrode as compared to dilute solution indicate that the dye molecules' state of aggregation and electronic structure have been modified upon adsorption to the surface. An increase in the molecular fluorescence is observed on the sulfur-modified gold electrodes, and is attributed to the intervention of the sulfur between the methylene blue and the metal surface. To avoid interference from the methylene blue fluorescence, er: situ SERS spectra were obtained with a Fourier transform (FT) spectrometer that utilized an excitation wavelength of 1064 nm. The FT-SERS spectra from methylene blue on sulfur-modified and bare gold surfaces exhibit differences that can be ascribed to the interactions of the dye molecules with the sulfur monolayer.