A Hemicyanin-Based Water-Soluble off-on Fluorescence and Colorimetric Probe for Detecting HSO₃^-/SO₃^2- in Real Samples

A fluorescence and colorimetric sensor (AHT) was developed to detect HSO₃^-/SO₃^2- in a 10 mM aqueous PBS buffer at pH 7.4. AHT exhibits non-fluorescence in the buffer due to the intramolecular charge transfer (ICT). The detection of HSO₃⁻/SO₃²⁻ by probe AHT occurs through nucleophilic addition to its carbon-carbon double bond, which disrupts conjugation and stops the ICT process. This reaction induced a visible color change from violet to colorless and activated fluorescence from "off" to "on" at 485 nm (λ_ex = 420 nm). The probe exhibited significant selectivity and sensitivity for HSO₃⁻/SO₃²⁻, with a detection limit of 51.5 nM and a rapid response time. Additionally, it effectively detected HSO₃⁻/SO₃²⁻ in real samples, e.g., sugar, water, wine, and biscuits.