Determination of hypochlorite and bisulfite in water by bifunctional colorimetric sensor based on octupolar conjugated merocyanine dyes

In this study, we developed a bifunctional colorimetric fluorescent sensor based on three merocyanine structures for the detection of hypochlorite (ClO-) and bisulfite (HSO3-). In MeOH solution and under special conditions, this sensor shows high selectivity on fluorescence and UV-Vis spectra for the detection of ClO- and HSO3-, respectively. The sensor solution exhibits a strong red fluorescence emission at 638 nm, which was quenched and the blue color turned to purple pink rapidly upon the addition of ClO-. The mechanism of the detection of ClO- was confirmed via ESI-MS that the C=C groups were induced to produce ethylene oxide and ethylene glycol derivatives by hypochlorite. The fluorescence emission at 638 nm in the concentration range of ClO- from 0 to 24 mu M showed a good linear relationship (R-2 = 0.9919), and the LOD of the sensor for ClO- was 0.42 mu M. Interestingly, the sensor can also detect HSO3- in acid condition (pH less than 7.4). The blue shift of UV-Vis spectra of the solution of sensor were observed after addition of HSO3- and irradiation with visible light for about 4 min. The HSO3- concentration showed a good linear relationship (R-2 = 0.9987) at 275 nm in the range of 12-42 mu M, and thus its LOD was calculated to be 1.14 mu M. Finally, the sensor has important value for detecting ClO- and HSO3- in tap water and lake water.

Automated summary

A bifunctional colorimetric fluorescent sensor based on three merocyanine structures was developed for the selective detection of hypochlorite and bisulfite ions. The sensor exhibited distinct fluorescence emission and UV-Vis spectrum changes when detecting ClO- and HSO3-, respectively. The sensor showed good linear relationships and low detection limits for both ions, making it valuable for water quality testing.