Electrochemical SERS of Self-Assembled Monolayer of Thiosalicylic Acid Adsorbed on Activated Gold Electrodes

A monolayer film of thiosalicylic acid (TSA) adsorbed on activated gold electrodes was investigated by using in situ electrochemical surface-enhanced Raman scattering (EC-SERS). In the SERS spectra of self-assembled monolayers in solutions with different pH values, two peaks with Raman intensities that decreased with increasing pH were observed. The optimum EC-SERS signals were obtained at 0.7 V and 70 s, and it was found that the intensities became weaker, and the peaks eventually disappeared, when the potential was negatively shifted. This showed that the alignments of TSA assembled on the gold surface changed in response to changes in the external conditions. The absorption mechanism of the TSA monolayer was investigated by calculating the distribution fraction of TSA at different pH values and the enhancement factor (EF) at different potentials, using a combination of SERS and EC-SERS. As a result of different electrochemical absorption orientations of TSA and its reduction/desorption behavior at high negative potentials, the Raman enhanced effect of TSA on gold was significantly reduced and the SERS activity was irreversibly lost.