Surface-Enhanced Raman Spectroscopy of Thionine-modified Gold Electrodes

Abstract

Surface enhanced Raman (SER) and resonance Raman (SERR) techniques have been used in situ to investigate thionine-modified gold electrodes. New surface roughening procedures for gold electrodes have resulted in an order of magnitude increase in the Raman signals. As a result of this, Raman spectra from leucothionine have been observed for the first time. The surface Raman spectra of both thionine and leucothionine are essentially unchanged over the pH range from 1.3 to 7 but both show major changes at pH 10. This behaviour has been rèlated to changes in the absorption spectrum of thionine at pH 1.0 where the compound is believed to exist as thionine hydroxide. At pH 1.3 and 7 the Raman signals from thionine arise from a combination of surface enhancement and resonance enhancement processes, whereas signals from leucothionine arise solely from surface enhancement. At pH 10 surface enhancement processes give rise to Raman intensity for both thionine and leucothionine.