Construction of a ratiometric probe with dual quenching mechanisms for selectively imaging intracellular sulfur dioxide overcoming the interference from cysteine

Endogenous sulfur dioxide (SO2) plays central roles in various biological and pathological events, and abnormal levels of SO2 can induce arterial hypertension, atherosclerosis, stenocardia, pulmonary arterial hypertension, and other diseases. In this work, a fluorescent probe with dual quenching mechanisms has been designed and synthesized, which selectively detected SO2 overcoming the interferences of Cys. The fluorescence of the probe was quenched by the intramolecular charge transfer (ICT) and internal rotation of vinyl group. Reaction with Cys only inhibited the internal rotation, and thus the probe-Cys displayed weak fluorescence. By contrast, addition of SO2 blocked the dual quenching processes and brought intense blue-shifted emission. The probe showed high selectivity, high sensitivity, fast response, and low cytotoxicity, and therefore the ratiometric imaging of intracellular SO2 has been achieved with the probe.