A ratiometric fluorescence probe for selective detection of sulfite and its application in realistic samples

A new fluorescent probe 7-(diethylamino)-3-((1e,3e)-5-oxo-5-phenylpenta-1,3-dien-1-yl)-2H-chromen-2-one (SPH), based on Michael addition mechanism, was designed and synthesized for selective detection of sulfite. The probe was constructed by incorporating an α,β-unsaturated ketone conjugated with a C˭C bond into the coumarin fluorophore as a specifical reaction site for sulfite utilizing its nucleophilic property. The extra conjugated C˭C bond induced obvious red-shifts in both absorption and emission maxima, and remarkably promoted the nucleophilic addition rate. Once treated with sulfite, the solution's color changed from orange to yellow companied with a strong blue-green fluorescence. The ratio of fluorescence intensity at 488nm and 630nm (I₄₈₈/I₆₃₀) was linear with sulfite concentration over the range of 0-80μM with a detection limit of 0.23μM. High selectivity and good competition of the probe toward sulfite over other anions and thiols enable us to monitor sulfite levels in realistic samples as well as in living HeLa cells.