Reversible CeO2–x and CeO2–x:Eu3+ Luminescent Hydrogen Peroxide Sensors with Recovery Rates Controlled by Temperature and UV Irradiation

Hydrogen peroxide (HP) plays an indispensable role in living organisms, being both an intracellular messenger and a substrate or byproduct of a number of enzymes. In this way, HP sensing is important for monitoring the activity of various cell systems and assessing the redox balance of the cell as whole. HP sensors based on luminescent inorganic nanoparticles can be considered as a prospective alternative to traditional dye- and enzyme-based sensors, which usually are unstable and nonreversible. The undoped (CeO2–x) and Eu3+-doped (CeO2–x:Eu3+) colloidal ceria nanoparticles studied in the paper provide HP detection by reversible quenching of Eu3+ (590 nm) and Ce3+ (430 nm) luminescence bands. The dynamics of Eu3+ and Ce3+ luminescence quenching and recovery during HP-nanoceria interaction provides an insight into the microscopic mechanisms of HP sensing by CeO2–x and CeO2–x:Eu3+ nanoparticles. Both CeO2–x and CeO2–x:Eu3+ luminescent sensors are reversible and their recovery rates can be sufficiently increased by temperature and continuous UV irradiation. At the same time, Eu3+ ions deteriorate the catalase-mimetic activity of CeO2–x NPs and worsen their antioxidant properties, which should be kept in mind while using these sensors in biological media.