Folic acid-conjugated graphene-ZnO nanohybrid for targeting photodynamic therapy under visible light irradiation

Nanoparticles are being increasingly recognized for their potential utility in biological applications including nanomedicine. The aim of this study is to investigate a new strategy to combine the ZnO nanoparticles with graphene for targeting photodynamic therapy (PDT) under visible light irradiation. Folic acid (FA), a targeting agent toward tumor cells, was conjugated onto graphene oxide (GO) via imide linkage. Using a simple and effective chemical precipitation method, a GO-FA-ZnO nanohybrid was then prepared. The combination of ZnO with GO-FA induced a remarkable improvement in tumor targeting, which has been demonstrated by the cellular uptake assay. Due to the high electrical conductivity of graphene, the interaction between graphene and ZnO, and the inhibition of aggregation, the hybrid of GO-FA and ZnO significantly enhances the photodynamic activity. It was noted that the photodynamic activity of the non-cytotoxic GO-FA-ZnO is mediated by reactive oxygen species (ROS) generation under visible light irradiation. Following the ROS generation, GO-FA-ZnO caused a significant decrease in cell viability, mitochondrial membrane potential, superoxide dismutase activity, catalase and glutathione peroxidase, as well as an increase in malonodialdehyde production. Moreover, GO-FA-ZnO induced apoptotic death by elevating the caspase-3 activity. The study presents a novel tumor targeting photosensitizer and a promising strategy in PDT for cancer treatment.