Colorimetric determination of dopamine by exploiting the enhanced oxidase mimicking activity of hierarchical NiCo2S4-rGO composites

A composite consisting of NiCo 2 S 4 and reduced graphene oxide (rGO) was prepared via a hydrothermal process. Compared to individual NiCo 2 S 4 nanomaterials or reduced graphene oxide, the composite exhibits enhanced oxidase-like activity. It is found that dopamine (DA) inhibits the ability of NiCo 2 S 4 -rGO to oxidize the substrate 3,3′,5′,5′-tetramethylbenzidine (TMB) to form blue colored ox-TMB. Based on these findings, a colorimetric method for determination of DA was worked out. The absorption, best measured at 652 nm, increases linearly in the 0.5–100 μM DA concentration range, and the limit of detection is 0.42 μM. This method was successfully applied to the detection of DA in spiked human serum samples. A hierarchical NiCo 2 S 4 -rGO composite was prepared through two-step hydrothermal process. It exhibits enhanced oxidase-like activity which, however, is inhibited by dopamine (DA). Hence, less blue colored ox-TMB is formed by oxidation of 3,3′,5,5′-tetramethylbenzidine in the presence of dopamine.