Saehan Choi1,Jeonga Kim1,Rafia Rahman1,Yoon Sung Nam1
Korea Advanced Institute of Science and Technology1
Saehan Choi1,Jeonga Kim1,Rafia Rahman1,Yoon Sung Nam1
Korea Advanced Institute of Science and Technology1
Wide bandgap semiconductor nanoparticles, such as zinc oxide (ZnO) and titanium dioxide (TiO<sub>2</sub>) nanoparticles, have been widely used as ultraviolet (UV) blocking materials due to efficient UV absorption and excellent stability. However, the high chemical potentials of the photo-induced electrons and holes unavoidably generate reactive oxygen species (ROS) that can induce adverse chemical and biological damage. Synthetic polymer encapsulation has been commonly used to suppress photo-induced ROS generation, but recent studies continue to warn against the use of synthetic polymers in cosmetic and personal care products. Here we present a new method to effectively minimize the photo-induced toxicity of TiO<sub>2</sub> using tannic acid, a bio-inspired adhesive antioxidant polyphenol molecule, that can strongly bind to TiO<sub>2</sub> nanocrystal surface via ligand-to-metal charge transfer (LMCT). SiO<sub>2</sub>-TiO<sub>2</sub> particles were prepared through the <i>in situ</i> TiO<sub>2</sub> nanocrystal synthesis within mesoporous SiO<sub>2</sub> particles to minimize the photochemical reactivity of TiO<sub>2</sub>. TA was spontaneously deposited on the TiO<sub>2</sub> surface by Ti-catechol and Ti-pyrogallol coordination to synthesize SiO<sub>2</sub>-TiO<sub>2</sub>-TA hybrid particles. TiO<sub>2</sub> nanoparticles penetrated the cellular membrane by endocytic internalization and accumulate around the endoplasmic reticulum and nucleus. Accordingly, fibroblasts treated with TiO<sub>2</sub> nanoparticles exhibited lower cell viability under UV or HEV light irradiation due to highly reactive ROS generation. However, SiO<sub>2</sub>-TiO<sub>2</sub>-TA hybrid particles did not penetrate the cell membrane but efficiently protected the fibroblasts against UV and HEV damage through the effective scavenging of photo-generated ROS. Additionally, the LMCT from the TA HOMO to the TiO<sub>2</sub> conduction band allowed a new absorption pathway, enhancing the UV-to-HEV blocking performance, which significantly increased the sunscreen performance of an emulsion formulation containing SiO<sub>2</sub>-TiO<sub>2</sub>-TA hybrid particles. This work demonstrated a new promising strategy of plastic-free sunscreen agents with enhanced sunblock performance and suppressed photochemically induced toxicity.