Herein, we report the synthesis of black gold nanoparticles via a facile, one-step green approach, resembling the traditional Turkevich synthesis. This approach is based on a simple mixing of the gold precursor salt and sodium citrate at room temperature in a basic pH. The black gold nanostructures are formed due to the assembly of in-situ formed small gold nanospheres, leading to the formation of nanowires. Such morphology provides SERS substrates with intense hot spots to efficiently generate hot charge carriers for performing chemical transformation of surface bound diazonium molecules monitored by Raman spectroscopy. First, the Raman spectra showed that the diazonium molecules are self-assembled in a dimer form, resembling the typical DMAB structures. Second, upon continuous excitation of the surface plasmon, the Raman peak assigned to the N=N vibrational modes decreases in intensity, while the C=C peak is broadened with time, suggesting the crosslinking of the adsorbed molecules accompanied by removal of the nitrogen. Additionally, by comparing the reaction behavior performed with external heating in dark and under irradiation, we show that the hot electrons play the dominant role to initiate the reaction.