Inhibition study of ZnMn2O4 with oxidase activity via Jahn-Teller effect for fast colorimetric sensing of uric acid.

ZnMn2O4 nanomaterial has outstanding advantages of environmental friendliness, low cost and ultra-high catalytic efficiency, and has become a potential candidate in the field of colorimetric detection. Herein, ZnMn2O4 nanoflowers with fluffy structure were synthesized by a simple one-pot hydrothermal method. It was found that the excellent oxidase (OXD) activity of ZnMn2O4 nanoflowers is not only attributed to the bimetallic synergistic effect between Zn and Mn, but also dominated by the Jahn-Teller distortion of Mn3+ with the t₂g3eg1 electronic configuration, which fills the gap in the structure-activity relationship of ZnMn2O4 nanozymes. However, the involvement of H2O2 could destroy the electronic configuration of Mn3+ thus decreasing the OXD activity gradient. The XPS peaks between ZnMn2O4and ZnMn2O4+ H2O2 systems were compared and analyzed in details. With the aid of density functional theory (DFT) calculations and density of states (DOS) analysis, we further clarify the intrinsic mechanism of H2O2-mediated OXD activity inhibition: H2O2 induces the valence state transition of Mn3+ to Mn2+, which weakens the Jahn-Teller effect of Mn3+ and damages the crystal structure of ZnMn2O4. Based on the above novel H₂O₂-mediated enzyme activity inhibition mechanism (different from the traditional peroxidase-based colorimetric strategy), a colorimetric sensor for rapid detection of uric acid was constructed within 19 min, and the limit of detection was as low as 0.22 μM. This sensor realizes a reverse signal response for uric acid detection, and exhibits superior performance in speed, sensitivity and anti-interference compared with reported colorimetric methods. This work not only expands the application prospects of ZnMn2O4 nanoflowers in biosensors, but also provides a new theoretical basis for the activity regulation of metal oxide nanozymes and a new technical approach for the rapid and sensitive detection of uric acid in the fields of medicine and biomedicine.