“Turn-On” Fluorescence Determination of β-Glucosidase Activity Using Fluorescent Polymer Nanoparticles Formed from Polyethylenimine Cross-Linked with Hydroquinone

β-Glucosidase is associated with many diseases, so it is important to be able to accurately determine β-glucosidase activity. Here, we describe a turn-on fluorescence method for sensitively determining β-glucosidase activity. The method involves the formation of water-soluble fluorescent polymer nanoparticles. β-Glucosidase initially hydrolyzes the β-arbutin substrate to release hydroquinone (1,4-dihydroxybenzene). The hydroquinone then forms cross-links between branched polyethylenimine molecules to give fluorescent water-soluble polymer nanoparticles. The polymer nanoparticles were found to fluoresce with excitation and emission peaks at 373 and 510 nm, respectively, and the fluorescence intensity was related to the β-glucosidase activity. The fluorescence intensity could therefore be used to determine the β-glucosidase activity. The lowest β-glucosidase activity that could be determined was 0.4 U L–1, and the dynamic linear range was 1.0–36.0 U L–1. The method was very selective for β-glucosidase activity and was not sensitive to other proteins. The method was successfully used to determine β-glucosidase in spiked samples containing human serum albumin at a concentration of 0.5%, and the recoveries were 95.2%–104.5%.