Ratiometric fluorescent probes with a self-immolative spacer for real-time detection of β-galactosidase and imaging...

Ratiometric fluorescent probes with a self-immolative spacer for β-galactosidase (β-gal) were developed. They function by β-gal-cleaving the β-galactoside bond of fluorescent substrates, followed by self-immolation to liberate the amino group of fluorophore. Thus, a remarkable variation in the photophysical properties was observed and the corresponding ratiometric detection of β-gal was realized. Our studies demonstrated that the GNPN exhibited high sensitivity for recognition of β-gal, with a detection limit as low as 0.17 U L^-1. GNPN can rapidly quantify β-gal enzyme activity; the emission ratio F₅₄₅/F₄₇₅ for the GNPN reached maxima after approximately 4 min, which was one of the shortest response time ever reported. Furthermore, we demonstrated that these probes possess excellent biocompatibility and can be used to visualize the endogenous β-gal in ovarian cancer cells.