An activated near-infrared fluorescent probe with large Stokes shift for discrimination of bio-thiols

Bio-thiols such as cysteine (Cys), homocysteine (Hcy), and glutathione (GSH) play a crucial role in physiological processes. Distinguishing between Cys, Hcy, and GSH remains a challenge because of their similar structure and reactivity. Herein, we conceptualized and synthesized a near-infrared (NIR) fluorescent probe TAI based on acridine-conjugated indole salts. This innovative probe demonstrated effectiveness in sensitively distinguishing Cys, Hcy and GSH by NIR dual-channel and time-dependence fluorescence. Probe displays a significant turn-on NIR fluorescent response toward Cys at 654 nm under 488 nm excitation with Large Strokes shift (about 166 nm) and high selectivity, but also shows turn-on NIR fluorescent response for Hcy/GSH at 695 nm under 640 nm excitation. More interestingly, the probe also exhibited an NIR fluorescence response at 654 nm to Hcy and no fluorescence response to GSH when the response time is over 3 h. The sensing mechanism was fully confirmed by NMR, HRMS spectra and DFT theoretical calculations. Moreover, successful intracellular imaging experiments in living cells suggest that the probe is suitable for discrimination imaging endogenous and exogenous bio-thiols. This work offers a promising near-infrared fluorescent imaging tool for the differential detection of bio-thiols.