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Small-molecular fluorescence sensors have become promising detection tools in many fields attributing to their high sensitivity, excellent temporal and spatial resolution, and low cytotoxicity. However, high concentration or aggregation-induced fluorescence quenching effect has usually hindered the development of traditional fluorescence dyes. Herein, a new fluorophore cyanovinylene dye BMZ with excimer emission property has been constructed. It shows an obvious enhanced and red-shift emission upon aggregation in aqueous solution, which overmatches the conventional pyrene with longer absorption and emission wavelengths. Using this unique optical property, a new fluorescence probe BMZ-Gal has been developed for trapping of β-galactosidase (β-Gal) activity with high selectivity, low limit of detection of 0.17 U, and rapid recognition, which is based on the β-Gal-induced formation of red-shift emitting excimer. β-Gal has a strong affinity for BMZ-Gal , which is verified through the Michaelis-Menten constants ( K m , 1.87 μM) and the hydrolysis efficiencies ( K cat / K m , 1.78 × 10 3 M -1 s -1 ). Furthermore, the assay system has been successfully used for detecting endogenous β-Gal in living ovarian cancer cells and can passively targeted to identify β-Gal in organelle level and determine its subcellular location with satisfactory accuracy. We anticipate that the new fluorophore cyanovinylene dye herein may inaugurate new opportunities for the development of excimer emission sensors.

5'-O-beta-D-Galactosyl-floxuridine, a potential novel prodrug, was synthesized with a yield of 75% through beta-galactosidase-catalyzed transgalactosylation. This enzyme displayed absolute regioselectivity toward the 5'-position of floxuridine. For the reaction, the optimal conditions were pH 6.5 at 45 degrees C for 60 h with floxuridine to o-nitrophenyl-beta-D-galactoside at 2:1 (mol/mol). Under these conditions, the initial reaction rate and the maximum yield were 0.28 mM h(-1) and 75%, respectively.