A novel dual-site fluorescent probe for the one-step detection of Cys and SO2 in living cells

Background Cysteine (Cys) is the major intracellular thiol and plays a key role in human pathology. Furthermore, endogenous sulfur dioxide (SO2) is produced in mammals. Abnormal levels of SO2 are commonly associated with a variety of respiratory, cardiovascular, and neurological diseases. Therefore, given their important role in life activities, it is significant to construct a fluorescent probe that can detection between Cys and SO2. Results We have designed and synthesized a two-site fluorescent probe <bold>CUM</bold> with coumarin derivative and benzaldehyde molecules, which can detect and differentiate between Cys and SO2 through dual excitation wavelengths. Its carbon-carbon double bond reacts with Cys and undergoes a nucleophilic reaction, emitting green fluorescence at 520 nm, while SO32- reacts with benzaldehyde molecules in the probe <bold>CUM</bold> and undergoes a blue fluorescence at 460 nm. SO32- reacts with the benzaldehyde molecule of probe <bold>CUM</bold> and fluoresces blue at 460 nm. Thus, the probe <bold>CUM</bold> with two reaction sites can distinguish between Cys and SO2 and shows good selectivity and fast reaction speed. In addition, we successfully utilized probe <bold>CUM</bold> to image Cys and SO2 in human breast cancer cells (MDA-MB-231). Significance This work provides an effective method for the molecular design of coumarin-based fluorescent probes. Probe <bold>CUM</bold> as a promising and reliable tool for the meticulous discrimination and quantification of Cys and SO2 in diverse biological matrices, thereby opening up new avenues for various biological systems.