Roles of Edges and Surfaces of Graphene Oxide in Molecular Recognition of Proteins: Implications for Enzymatic Inhibition of α-Chymotrypsin

Many biomedical applications of graphene oxide (GO) rely on GO-biomolecular interactions. These interactions can be tuned in two ways: (1) by controlling surface/edge ratio via tuning the lateral size and (2) through selective functionalization of edges or surfaces of GO. To probe this concept, we have prepared four different sizes of GO samples with variable lateral diameters to investigate the effect of surface/edge ratio of GO in protein surface binding. We have also examined the selective functionalization of GO either on edges or surfaces for biomolecular interactions. alpha-Chymotrypsin was used as a model protein, and activity assays were performed to analyze the role of surface and edges of GO in protein surface interactions. The results show that with increasing size, the inhibitory efficiency of GO was increased, most likely due to an increasing surfaceto-charge ratio. We have also observed that surface-functionalized GO shows higher inhibitory efficiency compared to edge-functionalized GO with similar amino acid- based functionality. Furthermore, the activity can be tuned depending on the amino acid side chains of functionalized GO, for which charge and hydrophobicity play the crucial role. Analysis of the kinetics indicates that the inhibition occurred through a reversible competitive binding with no effect on the protein's secondary structure. This modified GO can be used for other biomedical applications such as sensing, targeted delivery, etc. depending on the alteration of size and functionality or both of GO.