A sensitive electrochemical detection of metronidazole in synthetic serum and urine samples using low-cost screen-printed electrodes modified with reduced graphene oxide and C60.

Monitoring the concentration of antibiotics in body fluids is essential to optimizing the therapy and minimizing the risk of bacteria resistance, which can be made with electrochemical sensors tailored with appropriate materials. In this paper, we report on sensors made with screen-printed electrodes (SPE) coated with fullerene (C60), reduced graphene oxide (rGO) and Nafion (NF) (C60-rGO-NF/SPE) to determine the antibiotic metronidazole (MTZ). Under optimized conditions, the C60-rGO-NF/SPE sensor exhibited a linear response in square wave voltammetry for MTZ concentrations from 2.5 × 10-7 to 34 × 10-6 mol/L, with a detection limit of 2.1 × 10-7 mol/L. This sensor was also capable of detecting MTZ in serum and urine, with recovery between 94% and 100%, which are similar to those of the standard chromatographic method (HPLC-UV). Because the C60-rGO-NF/SPE sensor is amenable to mass production and allows for MTZ determination with simple principles of detection, it fulfills the requirements of therapeutic drug monitoring programs.

A simple electrochemical method to monitor an azo dye reaction with a liver protein.

Disperse Orange 37 (DO37) is an efficient azo dye for dyeing synthetic textile materials owing to its resistance to degradation that may also be harmful to humans as DO37 is not entirely eliminated in wastewater treatment. In this paper, we demonstrate that DO37 is bleached by reduced glutathione (GSH) in a reaction catalyzed by glutathione-s-transferase (GST), a phase II detoxification enzyme. The reaction included a nucleophilic attack involving sulfhydryl groups, confirmed using density functional theory (DFT) calculations. DO37 also induced quenching in the fluorescence of GST through static suppression. The reaction was determined using differential pulse voltammetry (DPV) by monitoring the oxidation peak at 0.65 V of GSH sulfhydryl group. Quantitative estimation of the product reaction could be made by measuring an additional oxidation peak at 0.91 V which increased linearly with DO37 concentration. These electrochemical determinations were made possible by preconcentrating the reaction product on a graphite-epoxy electrode with immobilization of GST onto magnetite nanoparticles. Straightforward biological implications from the results are associated with the known toxicity of azo dyes such as DO37, which has been proven here to interact strongly with both GSH and the liver enzyme GST, and may induce hepatocarcinogenesis or other types of cancer.