A Comparative Study of Modifying Gold and Carbon Electrode with 4-Sulfophenyl Diazonium Salt

A comparison of the reductive adsorption behavior of 4-sulfophenyl diazonium salt and subsequent electrochemical reactivity on gold relative to carbon was studied with some significant differences observed. The ability of the 4-sulfophenyl layer adsorbed onto gold to block access of the redox probe ferricyanide to the underlying electrodes, as determined via cyclic voltammetry was inferior to the same layers formed on glassy carbon electrodes thus indicating a more open, porous layer formed on gold. More significantly, the 4-sulfophenyl layers are shown to be far less electrochemically stable on gold than on glassy carbon. Electrochemical and X-ray photoelectron spectroscopy (XPS) evidence suggests the instability is due to cleavage of the bond between sulfonate functional group and phenyl ring. These results provide further evidence that although aryl diazonium salt layers are relatively stable on gold surfaces compared with alkanethiol based self-assembled monolayer (SAMs), the stability is not as high as is observed on carbon.