Enzyme-triggered fluorescence turn-off/turn-on of carbon dots for monitoring β-glucosidase and its inhibitor in living cells.

Energy transfer engineering based on fluorescent probes for directly sensing enzyme activities are in great demand as enzyme-mediated transformations, which are central to all biological processes. Here, a fluorescence carbon dot (CD)-based assay exhibiting selective responses to the quantitation of β-glucosidase and the effect of its inhibitor was developed. The most common substrate, para-nitrophenyl-β-d-glucopyranoside (pNPG) was hydrolyzed by β-glucosidase to release p-nitrophenol (pNP), which can efficiently quench fluorescence of CDs via an inner filter effect and electron transfer. However, in the presence of inhibitors of β-glucosidase, the fluorescence intensity gradually recovered as the concentration of inhibitors increased. Therefore, the enzyme-triggered fluorescence turn-off/turn-on of specific CDs successfully achieved sensitive detection of β-glucosidase and monitored the effect of its inhibitors. This new strategy was applied to detect β-glucosidase and monitor β-glucosidase inhibitor in hepatoma cells using cell imaging. All results suggest that the new method is sensitive and promising for use in cancer diagnosis and treatment.