Dual-mode colorimetric/fluorescence nitrite sensor enabled by CoFeMn hydroxide nanoflower nanozyme

A dual-mode sensor integrating colorimetric and fluorescent functionalities was constructed to enable sensitive, on-site visual detection of nitrite in food matrices, with CoFeMn hydroxide nanoflowers (CoFeMn HNFs) serving as a novel oxidase-mimicking nanozyme. First, the successful synthesis of CoFeMn HNFs was confirmed through a series of characterization techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). Then, the synthesized CoFeMn HNFs, which exhibit remarkable oxidase-like activity, effectively catalyzed the oxidation of 3,3’,5,5’-tetramethylbenzidine (TMB) to its blue oxidized form (ox-TMB) via the generation of superoxide anion radicals (O 2 • ⁻). Its K m and V max values reached 0.399 mM and 2.8 × 10 −7 M·s −1 , respectively, demonstrating not only significantly higher catalytic activity than horseradish peroxidase (HRP) but also efficient catalysis without the requirement of H 2 O 2 . In the presence of nitrite, ox-TMB undergoes a diazotization reaction to form yellow diazo products, accompanied by a distinct fluorescence quenching effect. In the colorimetric mode, the sensor exhibited an excellent linear response to nitrite over the concentration range 0.2 to 40 µg/mL, accompanied by a limit of detection (LOD) as low as 0.063 µg/mL. For the fluorescence mode, a superior linear range of 0.3 to 40 µg/mL was achieved, with a LOD of 0.223 µg/mL nitrite. The results generated by this dual-mode sensor for real food samples were highly consistent with the reference values from the national standard method, thereby confirming its accuracy and practical utility. This work presents a versatile, reliable, and cost-effective nanozyme-based platform that addresses a critical need for sensitive, rapid, and on-site nitrite monitoring in food products, with broad implications for improving food safety surveillance and protecting public health. Section Graphical