Preparation of carboxymethyl chitosan-Tb (CMCh-Tb) fluorescent probe: For high-sensitivity Cu detection and mechanism study.

Carboxymethyl chitosan (CMCh) is a natural polysaccharide derivative with biodegradability, rich in active amino and carboxyl groups. It can act as a ligand to coordinate with rare earth ions, transferring absorbed energy to the central ion to sensitize its luminescence. In this paper, CMCh-Tb was prepared as a solid fluorescent probe by mixing CMCh solution with Tb. The morphology, structure and properties of CMCh-Tb were characterized and analyzed by SEM, IR and XPS, and then the chemical structure of CMCh-Tb was determined. CMCh-Tb, as a highly sensitive fluorescent sensor for detecting Cu, has a detection limit (LOD) of 27.14 nmol/L. Through characterization using fluorescence spectroscopy, ultraviolet absorption spectroscopy, and fluorescence lifetime, we further explored the mechanism of Cu fluorescence quenching, finding that this process is primarily achieved through dynamic quenching. Additionally, we discovered that glutathione (GSH) can form a strong coordination with Cu, thereby inhibiting the quenching effect of Cu on the emission intensity of CMCh-Tb and restoring its luminescence characteristics. This finding indicates that CMCh-Tb can not only serve as a fluorescence sensor for detecting Cu but also as a reversible fluorescence sensor, significantly enhancing its performance in practical applications.