S‐Doping Regulated Iron Spin States in Fe−N−C Single‐Atom Material for Enhanced Peroxidase‐Mimicking Activity at Neutral pH

Abstract Designing biomimetic nanomaterials with peroxidase (POD)‐like activity at neutral pH remains a significant challenge. An S‐doping strategy is developed to afford an iron single‐atom nanomaterial (Fe₁@CN‐S) with high POD‐like activity under neutral conditions. To the best of knowledge, there is the first example on the achievement of excellent POD‐like activity under neutral conditions by regulating the active site structure. S‐doping not only promotes the dissociation of the N─H bond in 3,3″,5,5″‐tetramethylbenzidine (TMB), but also facilitates the desorption of OH* by the transformation of iron species’ spin states from middle‐spin (MS Fe^II) to low‐spin (LS Fe^II). Meanwhile, LS Fe^II sites typically have more unfilled d orbitals, thereby exhibiting stronger interactions with H₂O₂ than MS Fe^II, which can enhance POD‐like activity. Finally, a one‐pot visual detection of glucose at pH 7 is performed, demonstrating the best selectivity and sensitivity than previous reports.