Sequential and selective fluorescent detection of sulfur pollutants in environmental water using a dual-channel probe

Reactive sulfur species (RSS), including hydrogen sulfide (H 2 S) and bisulfite (HSO 3 - ), play critical roles in redox signaling, inflammation, and environmental toxicity. However, their structural similarity and frequent co-existence in complex matrices pose significant challenges for simultaneous and selective detection. Here, we report a novel dual-channel fluorescent probe, DSH, capable of logic-gated, sequential recognition of H 2 S and HSO 3 - with distinct optical outputs. DSH integrates a coumarin fluorophore and a 2,4-dinitrobenzenesulfonyl (DNP) group within a donor-π-acceptor (D-π-A) framework. Reaction with H 2 S cleaves the DNP unit, restoring intramolecular charge transfer (ICT) and inducing red fluorescence at 660 nm. Subsequent addition of HSO 3 - triggers nucleophilic addition at the coumarin double bond, disrupting π-conjugation and yielding yellow fluorescence at 560 nm. This stepwise transformation enables ratiometric dual-emission sensing and sequence-resolved detection of the two analytes. DSH exhibits high selectivity, rapid kinetics, and low detection limits (0.045 μM for H 2 S; 0.16 μM for HSO 3 - ). The sensing mechanism was validated by high-resolution mass spectrometry (HRMS) and 1 H nuclear magnetic resonance ( 1 H NMR) spectroscopy. Practical applicability was confirmed through successful detection in real water samples (tap, mineral, and river), with high recovery and reproducibility. Collectively, this study introduces DSH as a robust, logic-driven fluorescent platform for dual-target sulfur species monitoring in complex environmental systems.