A Benzothiazole-Based Fluorescent Probe for Ratiometric Detection of Al³⁺ in Aqueous Medium and Living Cells

Aluminum is the third (after O and Si) most abundant metal in the earth's crust and associates with neurological diseases when abnormal level of Al³⁺ occurs in nervous center. Developing highly sensitive and selective methods for Al³⁺ detection is of significant interest. In this work, we developed an excited state intramolecular proton transfer (ESIPT) and aggregation-induced emission (AIE) active fluorescent probe for ratiometric detection of Al³⁺ in aqueous medium and living cells. The BTZ-SF can detect Al³⁺ with high selectivity and a good linear relationship (R² = 0.9911) between fluorescence intensity ratio (I_{476 nm}/I_{568 nm}) and Al³⁺ concentration (0-100 μM). In addition, the detection limit was calculated as low as 2.2 μM. The single crystal structure of BTZ-SF-Al clearly exhibited the interaction between BTZ-SF and Al³⁺ with a hexa-coordinated structure. Furthermore, confocal fluorescence images of HeLa cell indicated that BTZ-SF could be used for monitoring Al³⁺ in living cells. Finally, a test strips experiment suggests that the BTZ-SF can recognize the Al³⁺ selectively accompanied by remarkable color change.