A novel ESIPT-ICT-based near-infrared fluorescent probe with large stokes-shift for the highly sensitive, specific, and non-invasive in vivo detection of cysteine

Water solubility, large Stokes-shift, and near-infrared emission are essential properties required for a fluorescent probe used for intracellular detection of the analytes. Herein, we report a new fluorescent probe, BMQA, obtained from the reaction of 2-(2-hydroxyphenyl) benzothiazole, methylquinoline, and acryloyl chloride. By using this probe, it is possible to quantitatively detect cysteine (Cys) in 1% acetonitrile-containing PBS buffer solution (pH 7.2). The experimental results showed that the probe exhibited an excellent spectral performance with an emission wavelength at 740 nm, Stokes shift of 310 nm, and detection limit of 0.062 mu M for Cys. Theoretical calculations were also conducted to clarify the luminescence mechanism of the system. In addition, the experiments performed on A549 living cells showed that BMQA is suitable for the in detection of Cys in human serum by fluorescence imaging.