Arylation of Au NPs with single diazonium salt (DZ) was achieved spontaneously by simple reaction of the NPs with diazonium compounds, under mechanical stirring in aqueous media. In a typical protocol: an aqueous solution of salt DZ was prepared at a set concentration in the 10 -3 -510 -5 M range, and added dropwise to the suspension of NPs. For this grafting, we prepared an aqueous mother solution of salt DZ at a concentration of 1 M which was diluted to reach the targeted concentration of diazonium compound: 50 µL of DZ solution were added to 50 mL of the gold NPs solution (20 nm-sized nanoparticles). The final concentration of AB salt in the reaction mixture was 10 -3 M. For the other concentrations, we proceeded in the same way by reducing the initial concentration of 10 -1 and 510 -2 M to the final concentrations 10 -4 and 510 -5 M, respectively.