Preparation of carboxymethyl chitosan-Tb3+ (CMCh-Tb3+) fluorescent probe: For high-sensitivity Cu2+ 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-Tb³⁺ was prepared as a solid fluorescent probe by mixing CMCh solution with Tb³⁺. The morphology, structure and properties of CMCh-Tb³⁺ were characterized and analyzed by SEM, IR and XPS, and then the chemical structure of CMCh-Tb³⁺ was determined. CMCh-Tb³⁺, as a highly sensitive fluorescent sensor for detecting Cu²⁺, 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 Cu²⁺ fluorescence quenching, finding that this process is primarily achieved through dynamic quenching. Additionally, we discovered that glutathione (GSH) can form a strong coordination with Cu²⁺, thereby inhibiting the quenching effect of Cu²⁺ on the emission intensity of CMCh-Tb³⁺ and restoring its luminescence characteristics. This finding indicates that CMCh-Tb³⁺ can not only serve as a fluorescence sensor for detecting Cu²⁺ but also as a reversible fluorescence sensor, significantly enhancing its performance in practical applications.