A Water-soluble Fluorescent Probe Based on Chitosan for Hypochlorite and Nitrite Detection

Hypochlorite and nitrite are commonly utilized in the food industry. Therefore, it is important to develop a low-cost, efficient, and rapid method to detect hypochlorite (ClO^-) and nitrite (NO₂^-). In this study, a novel fluorescent probe, CS-BP, was developed from chitosan (CS) by chemically incorporating phenothiazine derivatives (BP) through a Schiff base linkage. The probe exhibited a specific "turn-off" fluorescence response to ClO^- or NO₂^- with a color change from bright yellow to colorless. The detection limits of ClO^- and NO₂^- were 0.54 µM and 0.83 µM. By adjusting the pH of the CS-BP aqueous solution, ClO^- and NO₂^- could be effectively distinguished. A smartphone-based detection method was developed for rapid and portable analysis. Furthermore, CS-BP was successfully loaded onto test strips, cotton swabs, and fluorescent films, demonstrating excellent selectivity and versatility for detecting ClO^- and NO₂^- in complex samples. The results showed that CS-BP holds great potential for practical applications.