UV Protection and Antioxidant Activity of Nanodiamonds and Fullerenes for Sunscreen Formulations

Generation of reactive oxygen species (ROS) by common sunscreen agents such as titanium dioxide (TiO2) and zinc oxide (ZnO) has prompted much research to incorporate effective antioxidants into sunscreens. Nanodiamonds (NDs) and fullerenes (C60) are potent antioxidants (radical scavengers) and effective UV filters, making them prime candidates as additives. The radical scavenging potentials of NDs and C60 are compared to the common antioxidant vitamin C using the 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) assay. In the presence of UV irradiation and ROS-generating TiO2 nanoparticles, we found that the radical scavenging potentials of vitamin C significantly decrease, while those of NDs and C60 are enhanced. This suggests that NDs and C60 can be used as long-lasting antioxidants to complement sunscreens. NDs and C60 are further incorporated into prototype creams along with TiO2 nanoparticles. When these prototype creams are subjected to simulated solar irradiation, the transmission spectra show that the anti-UV properties of the creams are well maintained after prolonged irradiation. Hence, NDs and C60 are photostable UV filters, which can supplement the sun protection efficacy of sunscreens. Cell studies using human dermal fibroblasts are also conducted to demonstrate the ability of NDs and C60 to scavenge the intracellular ROS generated by TiO2 nanoparticles. Under irradiation, ND significantly reduces intracellular oxidative stress. This is not observed for C60 because it can behave as both a ROS generator and scavenger when irradiated. This work establishes the antioxidant and anti-UV benefits of adding NDs and C60 to sunscreens.