“…Note that the magnitude of peak current at −0.04 V is <0.15 μA at the scan rate of 100 mV/s, indicating that the surface concentration of the adsorbed species is very small. The oxidation of HT in aqueous solution depends on the pH and concentration of HT, and different products have been reported in the literature (vide infra) . 5,5‘-Dihydroxy-4,4‘-bitryptamine (DHB) and TAD are the two major products (Scheme ), which exhibit reversible voltammetric response in acidic and neutral pH. 37a,b,c As the voltammetric features for the GNPM and GNPW are closely similar to those of the two oxidation products of HT in aqueous solution, 37a,b,c we suggest that the voltammetric peaks ‘a' and ‘b' are attributed to the redox reaction (‘a' and ‘b' in Scheme ) of possible oxidation products TAD and DHB, respectively.…”