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

A composite consisting of NiCo2S4 and reduced graphene oxide (rGO) was prepared via a hydrothermal process. Compared to individual NiCo2S4 nanomaterials or reduced graphene oxide, the composite exhibits enhanced oxidase-like activity. It is found that dopamine (DA) inhibits the ability of NiCo2S4-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. Graphical abstract A hierarchical NiCo2S4-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.