A fluorescent dyad with large emission shift for discrimination of cysteine/homocysteine from glutathione and hydrogen sulfide and the application of bioimaging.

Biothiols, as reactive sulfur species (RSS), play important roles in human physiology, and they have a close connection of generation and metabolism pathways among of them. It is challenging to discriminate biothiols from each other due to the similar chemical structures and properties of them. Herein, we develop a fluorescent hybrid dyad (CS-NBD) for efficiently discriminating cysteine (Cys)/homocysteine (Hcy) from glutathione (GSH) and hydrogen sulfide (H2S) by a dual-channel detection method. CS-NBD performs inherently no fluorescence in ranging from visible to near infrared region. However, upon addition of Cys (2-150 μM)/Hcy (2-200 μM), CS-NBD generates significant fluorescence enhancement in two distinct emission bands (Green-Red), while encounter of GSH (2-100 μM) or H2S (2-70 μM) induces the fluorescence increase only in the red channel. The detection limit was determined to be 0.021 μM for Cys, 0.037 μM for Hcy, 0.028 μM for GSH, and 0.015 μM for H2S, respectively (S/N = 3). The interval distance between two emission bands is up to 163 nm, which is favourable to acquire the accurate data in measurement due to the reducing of crosstalk signals. CS-NBD is also successfully applied to distinguish Cys/Hcy in cellular context by dual-color fluorescence imaging.