A novel carbazole-based polymer and its hydrogel-assisted probe for portable detection of nitrite in food and water environment.

Nitrite is an extensively used food additive that is essential for preventing spoilage. However, its excessive residues in food pose significant threats to food safety and human health, necessitating portable and rapid tools for effective on-site monitoring. Herein, a novel carbazole-based polymer (Cz-P) with green fluorescence as the response signal under strongly acidic conditions was synthesized via Suzuki cross-coupling. Cz-P exhibits a green fluorescence quenching response to nitrite with excellent selectivity, high sensitivity (limit of detection: 0.07 μM), and rapid response (3 min). Moreover, Cz-P was successfully applied to quantify nitrite in real samples (including pickled vegetables, cured meats, and water samples). The detection mechanism of nitrite by Cz-P revealed that nitrite-induced fluorescence quenching occurs primarily via an electron transfer mechanism and hydrogen bonding interactions. Notably, a smartphone-assisted Cz-P/polyvinyl alcohol hydrogel-based sensor was constructed for portable and visual nitrite monitoring in food, offering a point-of-care testing tool for food safety.