Controlling the surface chemistry of cerium oxide nanoparticles for biological applications.

The catalytic activity of cerium oxide nanoparticles (CNPs) depends on the surface Ce3+/Ce4+ oxidation state. CNPs with a higher Ce3+ to Ce4+ ratio, oxygen vacancies and higher superoxide dismutase (SOD) mimetic activity are more effective against diseases associated with oxidative stress or inflammation. CNPs with a lower Ce3+/Ce4+ ratio show higher catalase mimetic activity and possess anticancer/antibacterial activity. However, different synthesis methods of CNPs and capping agents/surface coatings result in various Ce3+/Ce4+ oxidation states, thus limiting the use of particular CNPs for specific biological applications. In this study, we have shown that by selecting an appropriate doping method we can control the surface Ce3+/Ce4+ oxidation state to tune the catalytic activity and biological response. Importantly, superior SOD mimetic activity and efficient reactive oxygen species scavenging capability of one-step synthesized CNPs are linked to a uniform distribution of dopants in the CNP lattice and changes in the surface Ce3+/Ce4+ oxidation state.