Porous, Oxygen Vacancy Enhanced CeO2-x Microspheres with Efficient Enzyme-Mimetic and Photothermal Properties

Porous, defective, gray cerium oxide (g-CeO2-x) microspheres 4.8 mu m in size were synthesized as a multifunctional nanozyme with catalase-, peroxidase-, and oxidase-like activities by the reduction of monodisperse-porous cerium oxide (CeO2) microspheres. Higher Ce(III) atomic fraction, more oxygen vacancy, and lower oxygen content on the surface of g-CeO2-x microspheres were shown by Raman and X-ray photoelectron spectroscopy. Band gap energies of plain CeO2 and g-CeO2-x microspheres were determined as 3.0 and 2.4 eV, respectively. Reactive oxygen species (ROS) related to the enzyme-mimetic activity of g-CeO2-x microspheres were determined as singlet oxygen (O-1(2)center dot) and superoxide anion (center dot O-2(-)) by ESR spectroscopy. Michaelis-Menten plots sketched for catalase-, peroxidase-, and oxidase-like activities provided superior maximum substrate consumption rates for g-CeO2-x microspheres. Oxidase- and peroxidase-like activities were used for developing colorimetric and fluorometric protocols for the detection of nitrite as a common pollutant, respectively. g-CeO2-x microspheres also exhibited a photothermal response explained by enhanced light adsorption originated from more oxygen vacancies. A temperature elevation up to 19 degrees C was obtained under near infrared laser irradiation at 808 nm. Photothermal response accompanying with multifunctional enzyme-mimetic activities makes the porous nanozyme a promising synergistic therapy agent capable of overcoming hypoxia and generating additional ROS in a tumor microenvironment.

Automated summary

Porous and defective gray cerium oxide microspheres with multifunctional enzyme-like activities were synthesized by reducing monodisperse-porous cerium oxide microspheres. The microspheres had higher Ce(III) atomic fraction, more oxygen vacancy, and lower oxygen content on the surface. The band gap energy was smaller for the microspheres, indicating enhanced light adsorption. The microspheres exhibited superior enzyme-like activity for the detection of nitrite and could generate reactive oxygen species. Additionally, the microspheres had a photothermal response under laser irradiation.