Electrochemical evaluation of total antioxidant capacities in fruit juice based on the guanine/graphene nanoribbon/glassy carbon electrode

Based on electro-immobilization of guanine on graphene nanoribbon (GNR) modified glassy carbon (GC) electrode, a new electrochemical DNA biosensor was developed for the evaluation of total antioxidant capacities (TAC) in fruit juices. The biosensor relies on the guanine damage that is induced by hydroxyl radical (·OH) generated by Fenton-type reaction. Ascorbic acid (AA), which has the ability to scavenge the ·OH and to protect the guanine immobilized on the electrode surface, was used as the standard antioxidant to evaluate the TAC in fruit juice. Under optimized conditions, the proposed biosensor has excellent analytical performance for antioxidant capacity assessment: wide linear range (0.1 to 4 mg L−1), high sensitivity (4.16 μA/mg L−1) and low detection limit (0.05 mg L−1). Compared with the other electrochemical sensors developed previously, the proposed electrode demonstrates the improved detection limit of about 5 times to one order of magnitude for antioxidant capacity assessment. Additionally, the biosensor was successfully applied to the determination of the TAC in fruit juices.