Reduced graphene oxide enhances horseradish peroxidase stability by serving as radical scavenger and redox mediator

Graphene-based nanomaterials have been widely studied as high-performance matrices for enzyme immobilization and in the development of biosensors. Surface O-functionalities of graphene induce changes in chemical reactivity and electronic conductivity of nanomaterials and may interfere with enzymatic processes; however, the mechanisms are not fully understood. We compare the effects of three commercially available graphene-based nanomaterials, namely a graphene, a graphene oxide (GO), and a reduced graphene oxide (RGO), on the activity/stability of horseradish peroxidase. Both graphene and GO significantly reduced enzyme stability by altering enzyme conformation, which was evidenced by circular dichroism spectroscopy. However, RGO improved enzyme stability up to 7-fold. This increased stability was attributed to the capability of RGO to quench superoxide radicals, which were primarily responsible for the enzyme deactivation. The basal plane of RGO, mainly through quinone moieties, may act as a redox mediator to facilitate enzymatic turnover. Overall, the radical scavenging plus redox mediating capabilities of RGO suggest the potential for graphene-based nanomaterials to enhance enzyme engineering and enzyme-based sensors.