Skin friendly anti-photoaging semiconductor-nanozymes with dual enzyme activities

Skin photoaging, predominantly induced by UV light exposure, is a significant external factor to the aging process of the skin. Current anti-photoaging strategies primarily utilize semiconductor materials (e.g. TiO₂, ZnO) as UV light absorbers. However, these materials also generate reactive oxygen species (ROS) during UV absorption, potentially causing oxidative damage to skin cells. The development of UV absorption semiconductors with limited ROS generation is highly desired. Herein, inspired by the enzyme-mediated ROS clearance in living organisms, we propose to employ antioxidant nanozyme to build skin friendly anti-photoaging semiconductor nanostructures. As a proof of concept, CeO₂ nanozymes with dual enzyme activities were coated on the surface of TiO₂ semiconductor to build semiconductor-nanozyme core-shell nanostructures. The obtained TiO₂@SiO₂@CeO₂ (TSC) core-shell nanostructures exhibited enhanced UV light absorption capacity. They also possess significant SOD- and Catalase- like activity with the value of 5.63 U/mg and 5.11 U/mg respectively, and some of the catalytic kinetic parameters comparable to those of natural enzymes. The catalytic mechanisms were deciphered by the density functional theory (DFT) calculation, revealing that the (111) and (220) crystal planes contribute most to the enzyme-like activity of CeO₂. Besides, TSC could significantly reduce the UV light triggered intracellular ROS generation, and increased cell activity by 46% compared with the TiO₂ group. Moreover, TSC exhibited excellent anti-photoaging efficacy in mouse skin irradiation models. This study presents a safe and highly efficient nanostructure for skin anti-photoaging and offers a nanozyme-based solution to address the ROS-related side effects of semiconductor materials in biomedical applications.