Simultaneous Electrochemical Determination of L-Dopa and Melatonin Using RGO-Spinel Nanocomposite Decorated Pt Electrode

Abstract

Melatonin(N-acetyl-5-methoxy tryptamine) is a paracrine hormone secreted by pineal gland in the brain. This endogenous hormone has the ability to maintain the body circadian rhythm.1 3,4-dihydroxy-L-phenylalanine (L-Dopa) is the intermediate precursor of the Neurotransmitter dopamine. L-dopa, as one of catecholamines, is widely used as a source of dopamine in the treatment of Parkinson’s disease and epilepsy.2 Here, we report a sensor based on Platinum electrode modified with hydrothermally synthesized RGO and spinel nanoferrate for the simultaneous determination of L-Dopa and Melatonin.Graphene oxide (GO)is a graphene derived material with oxygen containing functional groups. Graphene is a material with honey comb like structure of carbon atoms having sp2 bonding character. It exhibits high electrical conductivity, thermal conductivity and mechanical strength. GO containing functional groups like –OH, -COOH etc., acts as the site for the nucleation of metal oxide nanoparticles. It improves direct electron transfer between the electrode and the redox species by accelerating the electron transfer and enlarging the effective surface area.3 GO was synthesized by modified Hummers method. Chemically converted graphene RGO has been prepared by various reduction methods such as chemical, microwave, electrochemical, thermal, solvothermal/hydrothermal, by reducing its oxygen content.4 Green synthetic pathway of hydrothermal method was adopted for RGO synthesis to avoid hazardous chemical species and vigorous reaction conditions. Spinel ferrate like Copper Cobalt ferrate (CuCoFe2O4) was synthesized by sol-gel method and RGO/Spinel nanocomposite was prepared by physical mixing.5 The synthesized materials were characterized using various techniques like FTIR, XRD, FESEM etc. The electro catalytic activity of RGO/Spinel nanocomposite anchored platinum electrode for the simultaneous determination of melatonin and L-Dopa was studied using several voltammetric techniques. Bare platinum electrode was able to sense melatonin and L-Dopa both individually, but not simultaneously. Compared to RGO modified Platinum electrode, RGO-Spinel ferrate/Pt electrode exhibited good response in terms of lower potential of electrooxidation of L-Dopa and Melatonin with enhanced catalytic current with a peak separation of 0.48V. This enhancement in electrochemical performance is due to the increase in surface area as well as conductivity of the electrode upon modification with RGO-spinel nanocomposite which act as an excellent electrochemical oxidant for L-Dopa and melatonin.