Determination of β-glucosidase activity using single-particle enumeration with Au@CeO₂ nanoparticles

A visible and sensitive assay for the quantitative detection of β-glucosidase (β-glu) activity based on Au@CeO₂ core-shell nanoparticles (Au@CeO₂ NPs) is described. As a hydrolytic enzyme, β-glu can promote the hydrolysis of β-arbutin to hydroquinone (HQ), which can trigger the decomposition of the CeO₂ shell. With the single-particle enumeration (SPE) strategy coupled with dark field optical microscopy (DFM), an obvious color alteration of single Au@CeO₂ NPs during the etching process can be observed in real-time. By statistically calculating the number of the etched nanoparticles, the β-glu activity level can be quantified accurately. This assay displays a broad linear range from 0.5 to 50 mU⋅mL^-1 and low detection limit of 0.12 mU⋅mL^-1. In addition, this method was successfully used to determine β-glu in real samples and acquires satisfactory recoveries in the range of 97.1-102.0%. This study provides a visualization analysis method for β-glu, which may be helpful for monitoring other targets in the future.