The rationale for using diazonium salts with hydrophilic heads was that in addition to binding to other functional groups, we could also maintain its dispersion in aqueous suspension. As aryl groups are known to form oligomers leading to a thick aryl layer and consequently passivation of the electrocatalysts, we have verified two routes: in the first one, diazonium concentration was monitored to reach a suitable thickness that ensures colloidal stability and also electrocatalytic activity. In the second approach, a refined strategy consisted in blocking the growth of the aryl layer by using two different diazonium salts; one bearing the COOH group and the other equipped with two methyl groups in meta positions of the diazonium salts in order to inhibit any oligomerization of the aryl groups at the surface of gold NPs. In this case, dual functionalization with two kinds of aryl groups permits to tune both colloidal stability and electrocatalytic performances of the Au NPs. The general strategy is schematically illustrated in Figure . In a first step, the well-known Turkevich method was adopted to design the Au NPs which were further grafted with aryl diazonium compounds; for the sake of simplicity, only the dual modification is displayed. In a third step, the GC electrodes were coated with diazonium-modified gold NPs for electrocatalyzed oxidation of ethanol. The whole strategy is simple and efficient. Hereafter, we shall describe the main experimental results pertaining to the characterization of the modified gold nanoparticles and their electrocatalytic performances. In Figure it can be seen different concentration of diazonium salt AB from 10 -3 to 510 -5 M grafted on gold NPs. In the higher concentration regime, i.e. 10 -4 and 10 -3 M, the UV-Visible spectrum shows a widening of the peak in the range of 600 to 700 nm and the more obvious shift which shows a weak aggregation of NPs . Figure displays the UV-visible spectra of NPs co-grafted with AB and DMB (1:4) diazonium salts at indicated concentrations. This figure also shows that higher concentrations of diazonium salts induce aggregated NPs with a peak or shoulder in the high wavelength at 600-700 nm, which will affect the catalytic activity. Figures show absorbance-vs-concentration linear correlations for gold NPs grafted with aryl groups (single and dual modifications) in the concentration of 510 -5 M.