Electrode potential effect on the molecular structure of adsorbed species at an interface is one of the most important issues in physical electrochemistry. In this study, shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) was used to probe the electrochemical potential effect on bonding with surface, ion-pairing, and molecular structure of a positive charge bearing self-assembled monolayer formed from N-(6-mercapto)hexylpyridinium (MHP) at a smooth gold electrode in aqueous perchlorate solutions. In situ electrochemical SHINERS results show that the Au–S stretching frequency exhibits near linear blue-shift as the electrode potential was tuned to more positive values. The frequency tuning rate was found to be as high as 18.6 ± 0.9 cm–1/V. Analysis of ion-pairing at the interface revealed a decrease in intensity of the vibrational spectrum of electrostatically attracted perchlorate anions as the electrode potential shifts progressively to more negative values. Spectroscopic evidence for poten...