Cerium oxide based nanozymes: Redox phenomenon at biointerfaces

Cerium oxide nanoparticles (nanoceria) are known to exhibit enzymelike activity, such as biological catalase, oxidase, superoxide dismutase, and peroxidase enzymelike activities. Catalytically active nanoceria offer several advantages over natural enzymes, such as controlled synthesis at low cost, tunable catalytic activities, as well as high stability against stringent physiological conditions. Exploiting these properties, several biomedical applications, such as biosensing, immunoassay, drug delivery, radiation protection, and tissue engineering, have been maneuvered. This review article provides a comprehensive summary of reported biological enzymelike activities of nanoceria and the possible mechanism of catalysis. It is also discussed that what physicochemical properties (surface charge, size, surface chemistry, and enzymelike activity) of nanoceria are altered when exposed to biologically relevant buffers and even in the mammalian cell cytoplasm. Based on various reports provided in the literature, these important issues need to be addressed. It has also been deliberated that in mammalian cells variations in properties of nanoceria observed are due to the intrinsic catalytic activity or as a result of downstream effects that could have emerged after the particles have interacted with biologic/environmental components. Such studies could be helpful in providing a better understanding the nanoceria's multienzyme-like activities and potential applications in the biomedical fields with special reference to damaging effects of free radicals in biological systems.