A Turn‐Off Fluorescent Probe for Hydrogen Sulfide With Smartphone‐Based Semi‐Quantitative Detection

The present study describes the design and synthesis of a turn‐off fluorescent probe, PPA , utilizing a Nile Red derivative as the fluorophore. PPA demonstrates highly specific recognition of H 2 S in HEPES buffer solution. Upon addition of increasing concentrations of H 2 S, the ultraviolet absorption at 570 nm decreases progressively, accompanied by a distinct color shift from purple to colorless, thereby allowing direct naked‐eye detection. Concurrently, the fluorescence emission intensity at 650 nm is significantly quenched. Under irradiation with 365 nm UV light, the solution transitions from emitting pink fluorescence to becoming nonfluorescent. The probe exhibits a short response time (15 min), excellent stability, and broad pH tolerance (3–10), along with high sensitivity, achieving a detection limit as low as 88.5 nM. Moreover, test strips and cotton swabs functionalized with PPA were successfully developed, facilitating rapid and semi‐quantitative detection of H 2 S in food samples with the assistance of a smartphone.