Chitosan-based fluorescent probe for the detection of Fe³⁺ in real water and food samples

Iron ions play a crucial role in the environment and the human body. Therefore, developing an effective detection method is crucial. In this paper, we report CNS2, a chitosan-based fluorescent probe utilizing naphthalimide as a fluorophore. CNS2 is designed to "quench" its own yellow fluorescence through the specific binding of compounds containing enol structures to Fe³⁺. Studying the fluorescence lifetime of CNS2 in the presence or absence of Fe³⁺ reveals that the quenching mechanism is static. The presence of multiple recognition sites on the chitosan chain bound to Fe³⁺ gave CNS2 rapid recognition (1 min) and high sensitivity, with a detection limit as low as 0.211 μM. Moreover, the recognition of Fe³⁺ by CNS2 had a good specificity and was not affected by interferences. More importantly, in this study, CNS2 was successfully utilised to prepare fluorescent composite membranes and to detect Fe³⁺ in real water samples and a variety of food samples. The results show that the complex sample environment still does not affect the recognition of Fe³⁺ by CNS2. All the above experiments obtained more satisfactory results, which provide strong support for the detection of Fe³⁺ by the probe CNS2 in practical applications.