Cationic red-emitting probes for the rapid and selective detection of SO2 derivatives in aqueous and cellular environments

Two water-soluble compounds based on a coumarin–pyridinium scaffold were synthesized for rapid and selective detection of sulfite. The detection strategy is possible through a Michael addition reaction of the sulfite to the cyano-vinyl double bond, distinguishable through the hypsochromic shifts in absorption and emission maxima. The probes exhibited high selectivity for sulfite, with a detection limit of 1.47 μM for dye 1 and 2.8 μM for dye 2 and a near instant response time of 10–20 seconds over other analytes and reactive sulfur species. Importantly, the probes also exhibit a robust colorimetric response in the presence of sulfite. Cellular imaging studies have demonstrated that the probes are non-toxic and suitable for the detection of sulfite levels in cells. Additionally, the probes have demonstrated sensitivity to detect endogenous sulfite levels in hepatic cancer cells.