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

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.