Asymmetric Oxygen Vacancy-Boosted Peroxidase-Like Activity of Zn-Doped Fe ₃ O ₄ Nanozyme for Colorimetric Detection of Uric Acid

Oxygen vacancy (O v ) can enhance the catalytic activity of a metal oxide nanozyme. However, in pure metal oxide, the highly symmetrical arrangement of cations surrounding the O v confines electrons within the vacancies, leading to low electron transfer efficiency. In this study, we engineered the asymmetric O v sites in Fe 3 O 4 nanoparticles by simple Zn doping and nitrogen-atmosphere annealing. The resulting Zn-doped Fe 3 O 4 (Zn–Fe 3 O 4 ) nanostructured microspheres featuring asymmetric oxygen vacancies (Zn–O v –Fe) exhibited peroxidase-like activity. The affinity of the Zn–Fe 3 O 4 nanozyme for H 2 O 2 molecules was ca. 30.6-fold that of Fe 3 O 4 nanoparticles. The superior catalytic activity is attributed to the asymmetric Zn–O v –Fe sites, where the electronegativity difference between Zn and Fe enhances the adsorption and polarization of H 2 O 2, thereby accelerating the cleavage of the HO–OH bond and generating more • OH radicals. Furthermore, by coupling the Zn–Fe 3 O 4 nanozyme with uric acid oxidase, we developed a colorimetric method for uric acid detection. In this work, a high-performance nanozyme was obtained through simple experimental steps using two inexpensive and environmentally friendly metals (Fe and Zn). More importantly, as a proof-of-concept, this work demonstrates that introducing asymmetric oxygen vacancies into metal oxides is an effective strategy for boosting the catalytic activity of nanozymes.