Enhancement in the Raman scattering of polypyrrole electrodeposited on roughened gold substrates coated with gold monolayers

In this study, polypyrrole (PPy) films were electrodeposited on gold substrates roughened by a triangular-wave oxidation-reduction cycle (ORC) in an aqueous solution containing 0.1 N HCl. Extending the applications of self-assembled monolayers, gold monolayers were then adsorbed onto PPy films by dipping the PPy-deposited gold substrates into Au complex-containing solutions, which were produced from the ORC procedure used in roughening the gold substrates. Encouragingly, the surface-enhanced Raman scattering (SERS) spectroscopy of PPy with this sandwiched structure, Au monolayers/PPy/roughened Au substrate, exhibits a higher intensity by 1 order of magnitude and a better resolution, as compared with the normal SERS of PPy electrodeposited on a roughened Au substrate. The enhanced SERS effects can be explained as the electromagnetic effect that correlates to both the Au monolayers above and the roughened Au substrate underneath. Moreover, the chemical effect, which is also contributive to the enhanced SERS effects, is first found from the phenomenon of charge transfer from the pyrrolylium nitrogen to the adsorbed Au-containing complex.