Amygdalin-Functionalized Carbon Quantum Dots for Probing β-Glucosidase Activity for Cancer Diagnosis and Therapeutics

A fluorescence active nanosystem capable of targeting specific receptors of cancer cells with or without a biorecognition element is advantageous for biosensor studies. Herein, a naturally occurring anticancer drug, amygdalin (synthetic form: Laetrile, a misnomer: vitamin B17), has been modified on the surface of carbon quantum dots, prepared by a hydrothermal method, to probe β-glucosidase activity. Despite its cyanide toxicity, amygdalin is recently revived to be an anticancer molecule, and the risk factor can be optimized by understanding its binding efficiency with β-glucosidase in the cancer cells. In this study, an in vitro biorecognition pattern of amygdalin-functionalized carbon quantum dots (Amy@CQDs) toward β-glucosidase is typically evaluated by an aggregation-induced fluorescence emission mechanism. The optical functionality and structural integrity of CQDs before and after functionalization with amygdalin are comprehensively studied by spectroscopic and microscopic techniques. Our results demonstrate that Amy@CQDs is a stable hydrophilic graphitic carbon nanostructure exhibiting selective fluorescence quenching upon interaction with β-glucosidase, enabling the lowest detection limit of 134 nM. Hydrolysis products of amygdalin mediated by β-glucosidase were further confirmed by HPLC and colorimetric methods, indicating the selective binding of the prepared Amy@CQDs, which may find a useful application in cancer diagnosis and therapeutics.