Sandwiched structure of Ag/polypyrrole/Au to improve the surfaced-enhanced Raman scattering

In this study, an increased surfaced-enhanced Raman scattering (SERS) of polypyrrole (PPy) based on a sandwiched structure of Ag/PPy/Au was first observed. First, a gold substrate was roughened by a triangular-wave oxidation-reduction cycle (ORC) in an aqueous solution containing 0.1 N KCl. Then, pyrrole (Py) monomers were autopolymerized on the roughened Au substrate due to the electrochemical activity of the species formed on the roughened Au substrate. Extending the application of self-assembled monolayers, silver monolayers were further adsorbed onto PPy films by dipping the PPy-deposited Au substrate into an Ag complex-containing solution, which was produced from roughening a silver substrate by using a similar ORC procedure employed in roughening the gold substrate. Encouragingly, the SERS spectroscopy of PPy with this sandwiched structure, Ag/PPy/Au, exhibits a higher intensity by 15-fold of magnitude and a better resolution, as compared with the normal SERS of PPy deposited on a roughened Au substrate. The enhanced SERS effects can be explained as both the electromagnetic one and the chemical one.