Rational design of near-infrared ratiometric fluorescent probes for real-time tracking of β-galactosidase in vivo.

β-Galactosidase (β-gal) is a hydrolytic enzyme in lysosomes and is also an important biomarker of cellular senescence and primary ovarian cancer. Therefore, real-time non-invasive detection of β-gal activity in vivo is of great significance for the prevention of cell senescence and early diagnosis of ovarian cancer. We designed an enzyme-activated proportional near-infrared (NIR) probe (Gal-Br-NO) for real-time fluorescence quantification and capture of β-gal activity in vivo. The main characteristics of the Gal-Br-NO probe include short response time (less than 10 min), large Stokes displacement (155 nm), and near-infrared fluorescence emission (670 nm). The probe has also been successfully used to detect β-gal in ovarian cancer cells and senile cells and can accurately detect endogenous β-gal in zebrafish. Our work provides a potential tool for pre-clinical real-time tracking of β-gal activity in vivo and early diagnosis of disease.