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.