The Role of the Surface Functionalities in the Electrocatalytic Activity of Cytochrome C on Graphene-Based Materials

The development of efficient electron transfer between enzymatic elements and the electrode is considered an important issue in the synthesis and design of bioelectrochemical devices. In this regard, the modification of the surface properties is an effective route to obtain a high-performance electrode using enzymatic elements. As we present here, understanding the role of surface functional groups generated by the electrochemical functionalization of graphene-based materials facilitates the design and optimization of effective electroactive bioelectrodes. In this sense, the surface chemistry directly influences the inherent electrocatalytic activity of cytochrome c (Cyt C) toward the electrochemical reduction of H₂O₂. Although the surface oxygen groups provide an immobilization matrix for the Cyt C in the pristine graphene oxide, the electrochemical functionalization with N and P species in one step significantly improves the electrocatalytic activity, since they may facilitate an optimal electrostatic interaction and orientation between the electrode material and the redox heme cofactor in the Cyt C, enhancing the electron transfer process. On the other hand, the lack of surface functional groups in the reduced graphene oxide does not favor the electron transfer with the Cyt C immobilized on the surface being completely inactive. Thus, the incorporation of surface groups using electrochemical functionalization with N and P species provokes a remarkable enhancement of the electrocatalytic activity of cytochrome c, up to four times more than the H₂O₂ reduction reaction. This demonstrated the effectiveness of the functionalization process and the impact in the electrochemical performance of Cyt C immobilized in graphene-based electrodes.