Ratiometric sensing of β-galactosidase based on excited-state intramolecular proton transfer (ESIPT) and solid-state luminescence enhancement†

Glycosidases play important roles in modulating the structural and functional integrity of glycoproteins and glycolipids, and thus are promising biomarkers for disease diagnosis. While current approaches for glycosidase detection mainly rely on an enhancement of the UV-vis absorbance or fluorescence emission of glycosyl indicators, here we develop a ratiometric fluorescent probe for the sensitive and selective detection of glycosidase activity based on the combined mechanisms of excited-state intramolecular proton transfer (ESIPT) and solid-state luminescence enhancement (SSLE). The probe behaves like a typical SSLE when glycosylated, and exhibits a ∼140 nm red-shift in fluorescence owing to activation of ESIPT after deglycosylation. Such a large Stokes shift may facilitate the unbiased analysis of glycosidase activities when used in diagnostic and drug-screening assays.