A novel rhodol-based colorimetric and ratiometric fluorescent probe for selective detection of sulfite in living cells

A new type of colorimetric and ratiometric fluorescent probe 1 for sulfite is developed based on a rhodol-benzothiazole platform. Ratiometric sensing of sulfite is achieved by utilizing the nucleophilic addition of sulfite to the vinyl bridge (‒C=C‒) to block the π-conjugated system of the probe, which results in significant blueshifts in the absorption and emission spectra of the sensing system (from 590 to 530 nm in the absorption spectra and from 650 to 555 nm in the emission spectra). This probe exhibits the desired selectivity for sulfite over other anions and biothiols. The fluorescence intensity ratio at 555 nm and 650 nm (I555/I650) increases linearly with the sulfite concentration in the range of 0.5‒15 µM with a detection limit of 0.28 µM. A cytotoxicity assay indicates that probe 1 has low cytotoxicity and good cell membrane permeability and can be used for sulfite detection in practical samples and for ratiometric fluorescent imaging of sulfite in living HepG2 cells.