Tuning Iron Spin State in Single-Atom Nanozymes Enables Efficient Peroxidase Mimicking

Although great progress has been made in nanozymes, their large-scale application still remains a huge challenge due to their unsatisfactory catalytic performances. Featuring unique electronic structure and coordination environment, single atoms nanozymes provide great opportunities to vividly mimic the specific metal catalytic center of natural enzymes and achieve the superior enzyme-like activity. Herein, spin-state engineering of single-atom nanozymes was employed for the first time to enhance peroxidase (POD)-like activity. Pd nanoclusters (PdNC) were introduced to rearrange spin electron occupation of Fe single atom (FeNC-PdNC), in which the electron-withdrawing properties of PdNC make the spin transiting of Fe single atoms from low spin to medium spin, facilitating the heterolysis process of H2O2 and the desorption of H2O. As a result, the spin-rearranged FeNC-PdNC displays superior H2O2 activating performance and kinetics to FeNC. Finally, FeNC-PdNC was applied to the immunosorbent assay for the colorimetric detection of prostate-specific antigen, achieving an ultralow detection limit of 0.38 pg/mL. Our findings provide a new paradigm for designing advanced enzyme mimics and allow to gain a deep insight into the catalytic mechanism of nanozymes.