Tuning iron spin states in single-atom nanozymes enables efficient peroxidase mimicking

The large-scale application of nanozymes remains a significant challenge owing to their unsatisfactory catalytic performances. Featuring a unique electronic structure and coordination environment, single-atom nanozymes provide great opportunities to vividly mimic the specific metal catalytic center of natural enzymes and achieve superior enzyme-like activity. In this study, the spin state engineering of Fe single-atom nanozymes (FeNC) is employed to enhance their peroxidase-like activity. Pd nanoclusters (Pd_NC) are introduced into FeNC, whose electron-withdrawing properties rearrange the spin electron occupation in Fe(ii) of FeNC-Pd_NC from low spin to medium spin, facilitating the heterolysis of H₂O₂ and timely desorption of H₂O. The spin-rearranged FeNC-Pd_NC exhibits greater H₂O₂ activation activity and rapid reaction kinetics compared to those of FeNC. As a proof of concept, FeNC-Pd_NC is used in the immunosorbent assay for the colorimetric detection of prostate-specific antigen and achieves an ultralow detection limit of 0.38 pg mL^-1. Our spin-state engineering strategy provides a fundamental understanding of the catalytic mechanism of nanozymes and facilitates the design of advanced enzyme mimics.