A portable film-based fluorescent sensor DIP@CP enables smartphone-assisted F⁻ visual detection in real samples via colorimetric and ratiometric fluorescent changes.

Abstract

Film-based fluorescent sensor DIP@CP was developed by incorporating the organic fluorophore DIP into a chitosan–polyvinyl alcohol (CS-PVA, CP) composite film. The sensor enabled selective and quantitative fluoride ion detection through dual-mode colorimetric and ratiometric fluorescent responses, facilitated by DIP’s favorable photophysical properties including near-infrared emission and large Stokes shift (>139 nm), which effectively reduced background interference. The detection mechanism relied on a specific F⁻-triggered Si–O cleavage, ensuring high selectivity. The composite film design enhanced portability for field applications, whereas integration with smartphone technology allowed for visual F⁻ detection by RGB analysis. Practical applications were successfully demonstrated in monitoring fluoride levels in diverse real-world samples, including water and commercial toothpaste samples.