Modulating Pt nanozyme by using isolated cobalt atoms to enhance catalytic activity for alleviating osteoarthritis

Combining the synergistic effect of single-atom catalysts and nanoparticles (NPs) to improve the catalytic activity may be promising in the design of nanozymes, although it only applies in the field of electrocatalysis. Herein, we designed a polyatomic SOD and CAT-mimicking Pt/Co-SA-NSG nanozyme composed of ultrafine Pt NPs and Co-SA-NSG with atomically dispersed Co and N, S co-doped graphene for OA treatment. Results demonstrated the Pt/Co-SA-NSG nanozyme has dual active centers containing Co-N4 and Pt and effective scavenging effect of reactive oxygen species (ROS), possibly due to that the electron orbital overlap between Co single atoms and Pt NPs enhanced the electron transport interaction to increase the adsorption energy of free radicals and reduce the reaction energy. Based on the H2O2 induced chondrocytes and OA joint model, Pt/Co-SA-NSG nanozyme exhibited biosafety, high photothermal conversion performance (54.56%), excellent SOD and CAT-like enzyme activities, and ROS scavenging ability. Particularly, in combination with NIR II irradiation therapy, Pt/Co-SA-NSG nanozyme could greatly relieved the OA progression with a Pelletier Score reduction of 54.54%. Mechanistically, the Pt/Co-SA-NSG nanozyme can restore mitochondrial function, thereby regulate ATP level, so as to reduce inflammatory factors level and increase antioxidant factors level. This novel nanozyme was expected to guide the design and activity enhancement of other nanozymes in the future.