A near-infrared fluorescent probe for the ratiometric detection and living cell imaging of β -galactosidase

β -Galactosidase ( β -gal) has captured the attention of biologists, chemists, and medical researchers as an important biomarker for cell senescence and primary ovarian cancer. Therefore, many fluorescent probes with visible light emission have been developed for the detection and imaging of β -gal in living cells. However, near-infrared (NIR) ratiometric probes are more suitable for bioimaging because near-infrared light can effectively avoid the interference of autofluorescence and the ratiometric approach can improve sensitivity and accuracy of the detection. In this work, we designed an NIR ratiometric probe ( TMG ) for the highly sensitive detection of β -gal. Using a spontaneous degradation mechanism based on the ICT effect, the change in ratio ( F 650 /F 580 ) exhibited a prominent β -gal-dependent performance and proved a strong linear response to the activity of β -gal at an enzyme concentration between 0 and 200 U L −1 , with a limit of detection as low as 0.86 U L −1 , and the response speed is much faster than the same type of probes previously reported. The probe also revealed an excellent biocompatibility and a large Stokes shift. Moreover, fluorescence microscopy imaging experiments confirmed that this probe could be successfully used for the detection of endogenous β -gal in living cells. Graphical abstract