Hollow Co–N/C biomimetic nanozyme-based smartphone dual-mode analytical platform: on-site quantification of nitrite in sausage

The excessive use of nitrite (NO 2 − ) has become a major food safety concern, posing a significant threat to public health. Therefore, developing a rapid, accurate, and on-site detection method for NO 2 − is of practical importance. Unlike peroxidase-mimicking nanozymes, oxidase-mimicking nanozymes can directly utilize molecular O₂ as an oxidant to produce ROS, eliminating the requirement for exogenous oxidants such as H₂O₂. Here, cobalt nitrogen doped carbon nanozymes (Co–N/C) with enhanced oxidase-like activity were synthesized by spatial confinement pyrolysis of ZIF-67. The hollow architecture of Co–N/C enhanced both the specific surface area and the density of active sites, thereby boosting oxidase-like catalytic performance. Substrate screening and theoretical calculations revealed that TMB exhibited the LUMO energy level (−0.0222 eV), lower than those of other tested substrates. Leveraging the diazotization reaction of NO 2 − , a paper-based visual detection platform was constructed, and enabling on-site quantification of NO 2 − . The method showed high selectivity, with a detection limit of 0.31 μM, well below national safety standards. This system was successfully applied to the determination of sodium nitrite in sausage, creating a promising strategy for the development of integrated, intelligent point-of-care testing systems.