Evaluating the antioxidant activity of secondary metabolites of endophytic fungi from Hypericum perforatum L. by an electrochemical biosensor based on AuNPs/AC@CS composite

Due to the variety and activity of secondary metabolites of endophytic fungi (SMEF) from medicinal plants, and the operation cumbersome of existing methods for evaluating the activity, there is urgent to establish a simple, efficient and sensitive evaluation and screening technology. In this study, the prepared chitosan functionalized activated carbon (AC@CS) composite as the electrode substrate material was used to modify glassy carbon electrode (GCE), and the gold nanoparticles (AuNPs) was deposited on AC@CS/GCE by cyclic voltammetry (CV). A ds-DNA/AuNPs/AC@CS/GCE electrochemical biosensor for evaluating the antioxidant activity of SMEF from Hypericum perforatum L. (HP L.) was fabricated using the method of layer by layer assembly. The experimental conditions affecting the evaluation results of the biosensor were optimized by square wave voltammetry (SWV) using Ru(NH3)63+ as the probe, and the antioxidant activity of various SMEF from HP L. was evaluated by the proposed biosensor. Meanwhile, the results of the biosensor were also verified by UV–vis. According to the optimized experimental results, the biosensors had a high levels of oxidative DNA damage at pH 6.0 and Fenton solution system with Fe2+ to OH− ratio of 1:3 for 30 min. Among the crude extracts of SMEF from roots, stems and leaves of HP L., the crude extracts from stems presents a high antioxidant activity, but it was weaker than l-ascorbic acid. This result was consistent with the evaluation results of UV–vis spectrophotometric method, also the fabricated biosensor presents high stability and sensitivity. This study not only provides a novel, convenient and efficient way for rapid evaluating the antioxidant activity of a wide variety of SMEF from HP L., but also provides a novel evaluation strategy for the SMEF from medicinal plants.