Gold nanoparticles/ZnO nanorods hybrids for enhanced reactive oxygen species generation and photodynamic therapy

Gold nanoparticles (Au NPs)@ZnO nanorods (NRs) hybrids, with various molar ratios of ZnO:Au, were developed to enhance generation of reactive oxygen species (ROS) for further application in photodynamic therapy (PDT). By introducing the metal/semiconductor heterostructure interface between Au NPs and ZnO NRs, the electron transfer was modulated under UV irradiation, which dramatically suppressed the electron-hole recombination in ZnO, and simultaneously increased the amount of excited electrons with high energy at Au NPs’ surface. Hence, the ROS yield of the nanohybrid was considerably improved compared with pristine Au NPs or pristine ZnO NRs, demonstrating the 1 + 1 > 2 effect. Moreover, such enhancement was strengthened along with the increase of Au proportion in the hybrid. It was exhibited that the Au@ZnO (ZnO:Au=20:1) acquired the highest ROS yield due to the largest interface area between Au and ZnO, which in turn led to the lowest cell viability for Hela and C2C12 cells during PDT. Besides, both ROS generation and cell destruction have positive correlation with nanohybrid dosage. The Au@ZnO hybrid (20:1,100 μg/ml) resulted in the Hela cell viability as low as 28% after UV exposure for 2 min, indicating a promising potential for therapeutic efficacy improvement in PDT.