Voltammograms (a-iv and a-v) were obtained with the modified electrode in presence of 0.5 and 1 M of ethanol, respectively. Adding 0.5 M ethanol (voltammogram a-iv) resulted in an increase in current intensity from 340 µA to 520 µA, and with an increase to 1 M of ethanol in voltammogram (Av), the current intensity is 723 µA at potential 1.497 V. In these two voltammograms also appeared a new oxidation wave noted at 0.2 V the current intensity of this wave increased with ethanol concentration. The voltammograms indicate that GCEs coated with the gold NPs are more active than the bare GCE for the oxidation of EtOH. Furthermore, there are 2 active oxidation potentials (0.2 V and 1.3 V vs. ECS) with these modified electrodes. Increase in the anodic current in the presence of ethanol shows that there is a catalytic activity in these potentials for electrooxidation of ethanol by gold NPs. Figure shows current-vs-EtOH concentration linear plots for GCE electrodes coated with gold NPs/AB and gold NPs/AB:DMB. The current intensity corresponds to the peak of ethanol electro-oxidation noted at 0.2 V (see Figure ). It is verified the current intensity of the oxidation wave as a function of the concentration of ethanol for gold NPs grafted with diazonium salt AB in different grafting concentration (Figure , a); these curves show that as the concentration of ethanol increases, the current intensity of the oxidation waves increases linearly. By increasing the initial diazonium salt concentration the current intensity of the oxidation wave decreases. For concentration 510 -5 M, the current intensity recorded with NPs/AB is very close to that obtained with ungrafted NPs. For co-grafted NPs by AB and DMB, we compared their catalytic activity in different total concentrations of diazonium salts and ethanol, under the same conditions (Figure ). From this comparison, it has been found that by increasing the concentration of the grafted salts on the NPs the catalytic efficiency decreases. Curves show two fold less catalytic efficiency for NPs/AB:DMB than NPs/AB when the diazonium initial concentration was 510 -5 M. It follows that dilution of the diazonium salt AB is more important than its mixture with DMB, another way to obtain absolute low initial concentration. Most probably this is due to hydrophobic effects induced by the two methyl groups borne by DMB and which hamper access of ethanol to the nanocatalyst surface. Elsewhere, it was demonstrated that hydrophobic aryllayer can constitute barrier layer to redox probes . By analogy, it could be possible that ethanol molecules are likely to remain in the aqueous solution, away from a relatively hydrophobic aryl capping layer thus inducing a loss in the alcohol oxidation peak intensity.