Sensitive Voltammetric Detection of Melatonin in Pharmaceutical Products by Highly Conductive Porous Graphene-Gold Composites

This work presents a novel melatonin sensor based on unfunctionalized macroporous graphene networks decorated with gold nanoparticles for the differential pulse voltammetric detection of melatonin in pharmaceutical products. Highly porous graphene structures were prepared by metallic template-assisted chemical vapor deposition, and their active surface area and electrocatalytic activity were improved by electrochemical deposition of gold nanoparticles (50–250 nm) on their struts. The graphene-gold electrodes present a highly sensitive performance toward electro-oxidation of melatonin with a wide linear range of 0.05–50 μM, a low detection limit of 0.0082 μM (3σ/m), and a significant sensitivity of 16.219 μA μM–1 cm–2. Therefore, the performance of the sensor regarding the obtained figures of merit is better than many other electrodes utilized for melatonin detection. The electrochemical active surface area of the glassy carbon electrode was multiplied by 18, and the high conductivity of gold-graphene composites and their synergistic catalytic effect lowered electron transport resistance by 87%. Moreover, long-term signal stability for about 14 days, acceptable reproducibility (relative standard deviation (RSD) of 4.70%), repeatability (RSD of 0.14%), and selectivity of the electrodes with various interfering materials are demonstrated. The valid potential application of the sensors for the determination of melatonin in pharmaceutical samples is shown.