β-Galactosidase activity monitoring and bioimaging by a novel ICT mechanism-based NIR fluorescent probe with large Stokes shift

β-galactosidase (β-gal) is known as a valuable biomarker of ageing and cell senescence, which is closely down-regulated with tumorigenesis and certain diseases. Thus, real-time and in-situ monitoring and bioimaging of β-gal activity is crucial to explore its important biological role in the diseases resulted from ageing and cell senescence. Here, an "off-on" near-infrared fluorescent probe, CPD-gal, was prepared for the monitoring of β-gal activity, which exhibited eye-catching selectivity and anti-interference ability, superior sensitivity (LOD = 6.0 × 10−4 U/mL) and large Stokes shift (133 nm). The fluorescence of CPD-gal was triggered by β-gal-catalyzed cleavage of galactosyl and activating inherent intramolecular charge transfer (ICT) process. Furthermore, the proposed fluorescent probe displayed excellent capacity of monitoring and imaging endogenous β-gal activity in cells and tumor-bearing mice, demonstrating its outstanding prospect in distinguishing senescent cells from normal cells.