A water-soluble near-infrared fluorescent probe for sensitive and selective detection of cysteine.

A near-infrared (NIR) fluorescent probe (Cys-AN) for selective and sensitive detection of cysteine (Cys) was designed and synthesized. The fluorescent probe was water-soluble and had a large Stokes shift of 150 nm, whose detection limit could reach to 0.96 μM in PBS buffer. After we analyzed the HRMS, TLC and optical data, a proposed sensing mechanism for the detection of Cys could result from the Michael addition and intramolecular cyclization reactions between the probe and Cys, followed by intramolecular charge transfer (ICT) process to afford the NIR fluorescent signal at 674 nm. Meanwhile, Cys-AN exhibited low cytotoxicity, and was successfully applied for bioimaging of Cys in living cells.