A fluorescent light-up probe with "AIE + ESIPT" characteristics for specific detection of lysosomal esterase.

We report a fluorescent light-up probe AIE-Lyso-1 for in situ visualization of lysosomal esterase activity. The probe is based on a salicyladazine fluorogen, which is conjugated with esterase reactive acetoxyl groups and lysosome-targeting morpholine moieties. The probe has characteristics of both aggregation-induced emission (AIE) and excited-state intramolecular proton transfer (ESIPT), which shows significant advantages, such as lysosome-specific targeting, no self-quenching at high concentration, excellent light-up ratio, large Stokes shift, low cytotoxicity, and high specificity to esterase. It has also been used for in situ monitoring of lysosomal esterase activity and tracking lysosomal movements in living cells, which has great potential for the diagnosis of Wolman disease caused by deficiency of lysosomal esterase.