A ratiometric fluorescent probe based on benzothiazole with a large Stokes shift for fluoride ion sensing in living...

The sensitive and selective detection of fluoride ions (F^-) is of great significance in both environmental and biological systems. A novel near-infrared ratiometric fluorescent probe, PC-SZ-TBS, was designed and synthesized by rationally linking dicyanoisophorone with 2-(2-hydroxyphenyl)benzothiazole. The probe operates via F^--triggered cleavage of the silicon-oxygen bond, resulting in a distinct fluorescence color change from yellow to bright red, along with significant fluorescence enhancement at 700 nm. Spectroscopic studies revealed that PC-SZ-TBS exhibits a low detection limit of 2.22 × 10^-6 mol L^-1 toward F^-, maintains excellent stability over a pH range of 4-10, and displays high selectivity with minimal interference from competing species. Biocompatibility assays demonstrated that PC-SZ-TBS possesses low cytotoxicity and robust cell permeability in 4T1 cells, as well as favorable imaging capabilities in living organisms including zebrafish and Arabidopsis thaliana, enabling effective visualization of F^- in biological tissues. Furthermore, PC-SZ-TBS was successfully applied to determine F^- in real samples such as tap water, lake water, Chinese baijiu, and various fruits. Integrated with a smartphone-based RGB analysis platform, a strong linear correlation between the R/G ratio and F^- concentration (R² = 0.9978) was established, allowing for real-time, portable semi-quantitative detection of F^-. This work provides a reliable and versatile tool for the visual monitoring of fluoride ions in both environmental and biological contexts.