Easy detection of S²⁻ using oxidase-like nanozymes of Fe,N co-doped hollow mesoporous carbon nanospheres via colorimetric method

The excessive presence of S²⁻ poses significant risks to human health and the environment. Therefore, the development of novel S²⁻ sensing methods remains crucial in daily life. Herein, Fe–N hollow mesoporous carbon nanospheres (Fe–N HMCNSs), characterized by a high specific surface area and excellent stability, were successfully prepared. Further investigation revealed that the colorimetric substrates such as 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonate) (ABTS), o-phenylenediamine (OPD), and 3,3′,5,5′-tetramethylbenzidine (TMB), can be effectively oxidized by Fe–N HMCNSs into colored products. Based on the oxidase-like activity of Fe–N HMCNSs, a facile colorimetric method for S²⁻ assay was constructed for the first time. The recognition of S²⁻ could be fulfilled by recording the absorbance intensity and observing color changes in nanozymes-based catalytic systems. This method is simple, cost-effective, and environment-friendly, offering a wide linear range (0.25–25 µM) and a low detection limit (42.2 nM) for S²⁻ assay. Furthermore, integration of smartphone-based RGB analysis enabled the portable and convenient S²⁻ sensing using the developed colorimetric sensor. The remarkable stability of Fe–N HMCNSs under harsh conditions endows their potential applications in the fields of food safety and environmental protection.