Carbon dots doped with nitrogen and boron as ultrasensitive fluorescent probes for determination of α-glucosidase activity and its inhibitors in water samples and living cells

An ultrasensitive fluorometric assay is described for the determination of the activity of the enzyme alpha-glucosidase in waters and living cells. Carbon dots doped with nitrogen and boron (N,B-CDs) were prepared that have excitation/emission peaks at 400/510 nm and a fluorescence quantum yield of 47%. 4-Nitrophenylglucoside is added and then hydrolyzed by alpha-glucosidase to form yellow 4-nitrophenol which screens off fluorescence due to an inner filter effect. The method was applied to the determination of alpha-glucosidase activity and has a 3 mU mL(-1) detection limit. It was subsequently applied to the determination of the alpha-glucosidase inhibitor acarbose which can be determined in a concentration as low as 10 nM (at three times the standard deviation versus slope). The method was also applied to the determination of alpha-glucosidase activity and acarbose in living HeLa cells and MCF-7 cells. The method is simple, sensitive, and excellently selective.