Histidine-functionalized graphene quantum dot-graphene micro-aerogel based voltammetric sensing of dopamine

Abstract

Histidine-functionalized graphene quantum dots (His-GQDs) made via thermal pyrolysis of citric acid and histidine are combined with Zn2+ ions to form Zn-His-GQD complex. The complex was employed as the solid surfactant for stabilizing toluene-in-graphene oxide aqueous dispersion emulsion. The graphene oxide in the Pickering emulsion was slowly reduced by addition of hydrazine hydrate and leads to the formation of graphene micro-gel. The micro-gel was treated by freeze-drying, acid washing and thermal annealing to obtain His-GQD-graphene micro-aerogel (His-GQD-GMA). The as-prepared hybrid offers a three-dimensional architecture with well-defined porous structures, in which the His-GQDs were well dispersed and fixed on the graphene sheets. The all-carbon hybrid provides excellent electron/ion conductivity, electro-catalytic activity and structural stability. The sensor based on the His-GQD-GMA exhibits ultrasensitive electrochemical response to dopamine. Its differential pulse voltammetric signal linearly increases with the increase of dopamine concentration in the range from 1.0×10−9M to 8.0×10−5M with the detection limit of 2.9×10−10M (at a S/N ratio of 3). The sensitivity is much better than that of the reported graphene sensors for dopamine. The analytical method has been successfully applied in the detection of dopamine in rat brain. The study also opens a window on the electronic properties of graphene aerogel and graphene quantum dots as well their hybrids to meet needs of further applications in sensors, catalysis and energy storage and conversion devices.