Red Light, Green chemistry: on-site nitrite detection in pre-processed vegetables using diazotization-active carbon...

Nitrite can be converted into carcinogenic substances under specific conditions, and non-standard operations in the production of pre-cooked meals may lead to the generation of nitrite, posing a hazard to human health. As a crucial component of pre-cooked meals, the nitrite content in pre-processed vegetables is directly linked to food safety. Therefore, conducting precise monitoring of nitrite levels in pre-processed vegetables and establishing highly sensitive, selective, and portable detection methods for nitrite ions are of great significance.

This study developed a smartphone-integrated fluorometric/colorimetric dual-mode sensor using amino-functionalized carbon quantum dots (OPD-CQDs) for rapid, on-site nitrite detection in pre-processed vegetables. OPD-CQDs, synthesized via solid-phase calcination of o-phenylenediamine, exhibited strong acidic fluorescence and underwent a nitrite -triggered diazotization reaction, causing blue-to-colorless transitions and fluorescence quenching. Smartphone-based RGB analysis converted fluorescence and colorimetric signals into quantitative nitrite values, achieving detection limits of 0.06 μM and 0.02 μM, respectively. A composite starch gel test strip (MO/OPD-CQDs, MO: methyl orange) showed distinct color shifts from purple to light yellow with increasing nitrite concentrations. The sensor was validated for accuracy and practicality in three commercial pre-processed vegetables, demonstrating high selectivity and sensitivity.

Compared to traditional methods, the proposed sensor offers superior sensitivity, portability, and cost-effectiveness, making it suitable for on-site food safety monitoring. Its integration with smartphone technology bridges laboratory precision with field applicability, offering a real-time solution for food safety monitoring.