Designing of a high-performance fluorescent small molecule enables dual-mode and ultra-sensitive fluorescence visualizing of HSO and HClO in dried fruit, beverage, and water samples.

Herein, a novel hemicyanine derivative (E)-3-(1,1-dimethyl-2-(4-(methylthio)styryl)-1H-benzo[e]indol-3-ium-3-yl)propane-1-sulfonate (BIS) has been reasonably designed. Compound BIS is long-wavelength emissive and water-soluble with a large Stokes shift. Intriguingly, probe BIS provides a dual-mode fluorescence response pattern for the sensing of bisulfite (HSO) and hypochlorous acid (HClO) with great limit of detections (3.6 and 57.4 nM). First, the 1,4-Michael addition of HSO on the conjugated double bond triggers a ratiometric response (I/I). Second, the rapid oxidation of HClO on the thioether moiety provides a turn-on response (I). Evaluation of HSO and HClO levels in dried fruit, beverage, and water samples has been carried out with satisfactory results. Moreover, motivated by an impressive chromatic variation (red to blue), smartphone-assisted signal readout system and thin-film sensing platform are facilely constructed for real-time and on-site measurement of HSO levels. Furthermore, probe BIS is used for the in vivo imaging of HSO in edible fish models.