Rapid detection of intracellular Cys over Hcy and GSH using a novel two-photon coumarinocoumarin-based colorimetric and fluorescent probe

Due to the good biological properties of coumarinocoumarin and the importance of cysteine (Cys) in organisms, a novel coumarinocoumarin-based probe (CCx) has been designed and synthesized for detecting intracellular Cys. CCx was prepared as a latent fluorescence probe from salicylaldehyde using a simple 3-step procedure to achieve a large Stokes shift (90 nm), high sensitivity (LOD 388 nM) and a fluorescent turn-on response (F/F0 = 15) towards Cys. Owing to the specific conjugate addition-cyclization reaction between Cys and an acrylate moiety, CCx displayed high selectivity toward Cys over other various natural amino acids under physiological conditions. Then, CCx was successfully used for the fluorescence imaging of Cys in HeLa cells, and a rapid response was observed after incubation with CCx for 5 min. Furthermore, two-photon fluorescence images of mice tumor tissues were obtained, and the viability was measured to be more than 80%, which shows that CCx can be used as a rapid and biocompatible probe for Cys in vivo.