Proton Driving Mechanism Revealed in Sulfur-Doped Single-Atom FeN2O2 Carbon Dots for Superior Peroxidase Activity.

Heteroatom-doped single-atom nanozymes (SAEs) hold great promise as enzyme mimics, yet their catalytic mechanisms remain unclear. This study reveals that the proton driving mechanism induced by sulfur doping in single-atom FeN2O2 carbon dots (S-FeCDs) significantly enhances peroxidase (POD)-like activity. Synthesized via low-temperature carbonization, S-FeCDs exhibit FeN2O2 coordination with sulfur in the second shell, as confirmed by XAFS and AC-STEM. The POD-specific activity of S-FeCDs reached 295 U/mg, which is 11.2-fold higher than that of sulfur-free FeCDs, with natural enzyme-like kinetics. In situ experiments, kinetic and mechanistic studies revealed that sulfur doping promotes H2O dissociation, enhances H+ adsorption, reduces the ΔG for H2O2-to-·OH conversion. DFT revealed a lowered energy barrier for the rate-determining step (2*OH → *O+*H2O) from 2.50 eV to 1.62 eV. In vivo, S-FeCDs demonstrated broad pH efficacy in MRSA-infected wound models, achieving near-complete healing within 7 days. The proton driving mechanism was further validated through nitro compound reduction, demonstrating accelerated N-H bond activation. This work highlights the critical role of sulfur-induced proton dynamics in enhancing SAEs performance, providing a rational strategy for designing multifunctional nanozymes in biomedical and catalytic applications.