Local geometric configurations of metal cations in inorganic
enzyme
mimics determine their catalytic behaviors, while their optimization
remains challenging. Herein, kaolinite, a naturally layered clay mineral,
achieves the optimization of cationic geometric configuration in manganese
ferrite. We demonstrate that the exfoliated kaolinite induces the
formation of defective manganese ferrite and makes more iron cations
fill into the octahedral sites, significantly enhancing the multiple
enzyme-mimicking activities. The steady-state kinetic assay results
show that the catalytic constant of composites toward 3,3′,5,5′-tetramethylbenzidine
(TMB) and H2O2 are more than 7.4- and 5.7-fold
higher than manganese ferrite, respectively. Furthermore, density
functional theory (DFT) calculations reveal that the outstanding enzyme-mimicking
activity of composites is attributed to the optimized iron cation
geometry configuration, which has a higher affinity and activation
ability toward H2O2 and lowers the energy barrier
of key intermediate formation. As a proof of concept, the novel structure
with multiple enzyme-mimicking activities amplifies the colorimetric
signal, realizing the ultrasensitive visual detection of disease marker
acid phosphatase (ACP), with a detection limit of 0.25 mU/mL. Our
findings provide a novel strategy for the rational design of enzyme
mimics and an in-depth investigation of their enzyme-mimicking properties.