A Two-Site Fluorescent Probe for Cys/Hcy and SO2 Detection and Its Application in Cells and Zebrafish

Cysteine (Cys) and homocysteine (Hcy) are major intracellular thiols that play a key role in human pathology. Sulfur dioxide (SO2) can be produced endogenous in mammals. SO2 and its derivatives play a crucial role in regulating a wide range of physiological processes. The abnormal level of SO2 is commonly associated with a number of respiratory, cardiovascular and neurological diseases. In view of their vital roles in biological systems, it is of great significance to construct a fluorescent probe that can make a distinction between Cys/Hcy and SO2. Herein, a two-site fluorescent probe (HM-NBD) with coumarin derivative moiety and NBD moiety was designed and synthesized. Free HM-NBD had no fluorescence. The ether bond of the HM-NBD can be cut off after reacting with Cys/Hcy. After NBD fell, Cys/Hcy further rearranged with NBD and emitted green fluorescence at 540 nm. The SO(3)(2-)reacted with the carbonyl group of the HM-NBD and released orange fluorescence at 590 nm. Thus, HM-NBD with two reaction sites can distinguish Cys/Hcy and SO2, and showed good selectivity and quick response speed. Moreover, we succeeded in applying HM-NBD to image Cys/Hcy and SO2 in HepG-2 cells and zebrafish.