A flexible dual-readout sensor based on Mn-doped CeO₂ Nanozymes for selective nitrite monitoring in pickled...

A rapid and flexible visual sensing patch was developed for nitrite detection by integrating Mn-doped CeO₂ with a polyacrylamide (PAM) hydrogel. The incorporation of Mn into the CeO₂ lattice significantly enhances oxidase-like activity by facilitating electron transfer between Ce and Mn redox couples. The PAM hydrogel confines both CeO₂ and NO₂^- within its three-dimensional network, which promotes rapid mass transfer and leads to the amplification of reaction rate. Moreover, the flexible sensing patch enables not only UV-Vis spectroscopic analysis but also rapid on-site screening via smartphone-based colorimetry. The visual sensor exhibits high sensitivity, selectivity, anti-interference capability, and a low limit of detection (LOD = 0.122 μM) for NO₂^-. The as-prepared sensing patch demonstrated satisfactory reliability in quantifying NO₂^- in real food samples such as pickled vegetables.