Simultaneous determination of 5-hydroxytryptamine and dopamine using ionic liquid functionalized graphene

An electrochemical sensor for simultaneous determination of 5-hydroxytryptamine (5-HT) and dopamine (DA) was developed in this paper based on an ionic liquid functionalized-graphene (IL-graphene) modified glassy carbon electrode. Transmission electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis were used to characterize the formation of the IL-graphene composites. Due to functionalization of the ionic liquid, IL-graphene can not only be dispersed well in aqueous solutions, but also exhibit a strong positive charge. Cyclic voltammetry and differential pulse voltammetry results demonstrated that 5-HT and DA can be detected selectively and sensitively at the constructed electrode with peak-to-peak separation about 164 mV. Under the optimized condition, the linear responses were obtained in the range of 2.0 × 10−7 to 1.0 × 10−5 M with a detection limit of 6.7 × 10−8 M for 5-HT, and in the range of 1.0 × 10−6 to 1.0 × 10−4 M with a detection limit of 3.3 × 10−7 M for DA (S/N = 3), respectively. Moreover, the designed sensor was further applied to the simultaneous determination 5-HT and DA levels in human serum samples with reliable recovery. The excellent performance of this sensor was ascribed to the network-like structure of IL-graphene which provided large surface area to contact 5-HT or DA.