A chitosan-based fluorescence probe for the detection of nitrite in food samples

Polysaccharides, as a natural biomolecule, are abundantly available in nature and have good bioactivity. They contain several functional groups such as hydroxyl, carboxyl, and amino groups, which can exhibit different fluorescent property after modification. In this work, the chitosan (CS) was selected as a raw material and grafted with methotrexate (MTX) to prepare a nitrite sensor. The sensing material exhibited obvious aggregation-induced emission (AIE) properties and could react with nitrite under acidic conditions to form diazo compounds that could enhance fluorescence. This "enhanced-luminescent" mode fluorescence probe for nitrite (NO₂^-) displayed superior sensing performance, such as excellent sensitivity, good selectivity, a low detection limit (0.22 μM) and wide detection range from 0 to 120 μM. Moreover, this sensor was effectively applied to detect nitrite in sausage samples. Finally, CS-MTX also showed excellent biocompatibility, good water solubility and outstanding antibacterial performance against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli). These results demonstrated that it may be a potent multifunctional material for nitrite detection and anti-bacteria in food industry.