Metal nanoparticles are systems largely employed in surface-enhanced Raman spectroscopy (SERS). In particular, gold nanoparticles are one of the best substrates used in this field. In this work, the optimal conditions for gold nanoparticles electrodeposition on single-walled carbon nanotubes electrodes have been established to obtain the best SERS response. Using this substrate and analyzing the changes of in situ Raman spectra obtained at different potentials, we have been able to explain simultaneously the oxidation mechanism of purine bases, differentiating the oxidation intermediates and their orientation during the different oxidation steps. Adenine orientation hardly changes during the whole oxidation; the molecule maintains a parallel configuration and only shows a slightly tilted orientation after the first oxidation step. On the other hand, guanine orientation changes completely during its oxidation. Initially, guanine is perpendicular respect to gold nanoparticles, changing its orientation after the first oxidation process when the molecule shows a slightly tilted orientation, and it finishes parallel respect to the electrode surface after the second oxidation step.
