Metallothionein-Inspired Asymmetric Heteroatom Doping of Single-Atom Nanozymes for Multi-Enzyme Biocatalysis

Single-atom catalysts (SACs) exhibit enzyme-mimicking activity but are often limited by single-enzyme-like functions and modest catalytic efficiency. Here, a metallothionein-inspired heteroatom doping strategy is reported to construct asymmetric Fe single-atom catalysts (FeN₃S). Fe³⁺ is coordinated with cysteine via strong mercaptide bond formation, followed by zeolitic imidazolate framework-8 (ZIF-8) biomineralization and pyrolysis. The FeN₃S catalyst displays markedly enhanced multi-enzyme activities-including NADH oxidase-, oxidase-, peroxidase-, and catalase-like activities-with 1.35-4.60-fold improvements compared to sulfur (S)-free analogues. This high multi-enzyme efficiency arises from i) atomically dispersed Fe from biomineralization; ii) the large surface area and pore volume retained from the original metal-organic framework, and iii) the S-doping achieved through the strong mercaptide coordination between Fe and S. The S doping not only tunes electronic structure of Fe single atom to reduce activation barriers and enhances substrate interaction, but also facilitates charge transfer. As a result, FeN₃S induces ≈90% tumor cell suppression within one day through reactive oxygen species generation and disruption of the NADH/NAD⁺ balance, highlighting its strong potential for cancer therapy. This work provides a bioinspired strategy for advancing SACs toward multifunctional biocatalysis and biomedical applications.