A Self-antibacterial Chitosan-based Polymeric Fluorescent Probe with a Dual-lock Strategy for Ultrafast Detection of Fe³⁺ in Water System

In this work, a novel polymeric fluorescent probe, chitosan grafting coumarin-3-carboxylic acid (CSC) was designed and synthesized by a one-step condensation in solution. The probe exhibited dual functionality, serving as a highly selective sensor for Fe³⁺ and demonstrating intrinsic antibacterial activity. Coumarin modification imparts unique morphological characteristics and enhances water solubility in chitosan. The CSC probe demonstrated blue fluorescence quenching upon Fe³⁺ addition, and the presence of multiple binding sites for Fe³⁺ on the chitosan chains endowed CSC with rapid recognition capability (within 30 s) and high sensitivity detection limit (2.58 µmol/L). The ultrafast and specific detection of Fe³⁺ was attributed to the dual-lock coordination cage formed between the abundant hydroxyl groups of chitosan and the carbonyl group of coumarin. Fluorescence quenching primarily originates from the fast formation of complexes via effective orbital overlap and excited-state electron transfer from the fluorophore to Fe³⁺. Its good photostability and acceptable reusability confirm its potential for practical and cost-effective sensing applications. The CSC probe was successfully applied for the quantitative detection of Fe³⁺ in real water samples and the study of effective antibacterial activity. This work presents a multifunctional platform that combines sensitive metal ion sensing with antimicrobial properties, which holds significant promise for environmental monitoring and biomedical applications.