A ratiometric fluorescent biosensor for the sensitive determination of α-glucosidase activity and acarbose based on N-doped carbon dots

In this work, a novel ratiometric fluorescent platform for alpha-glucosidase (alpha-glu) and its inhibitor was constructed based on N-doped carbon dots (N-CDs). The alpha-glucosidase present can catalyze the release of hydroquinone (HQ) from alpha-arbutin. Then, the generated HQ can be oxidized and copolymerized with polyethyleneimine (PEI) to form a yellowish green fluorescence copolymer (PHQ-PEI) with intense fluorescence emission at 510 nm. When the P(HQ-PEI)was formed, blue fluorescence of N-CDs at 425 nm was decreased, whereas the fluorescence of P(HQ-PEI)at 510 nm increased sharply as a result of the fluorescence resonance energy transfer (FRET) effect between N-CDs and PHQ-PEI. However, in the presence of acarbose, the activity of alpha-glucosidase is inhibited, and alpha-arbutin cannot be hydrolyzed to hydroquinone, leading to the fluorescence recovery of N-CDs at 425 nm and the fluorescence decrease of P(HQ-PEI)at 510 nm. The linear range from 0.2 to 1.6 mU mL(-1)and 25-150 mu mol L(-1)was obtained for alpha-glucosidase and acarbose detection, respectively, and the detection limit (LOD) for alpha-glucosidase and acarbose was as low as 0.082 mU mL(-1)and 14.5 mu mol L-1. Thus, a ratiometric fluorescent sensor with good sensitivity and high specificity was established for alpha-glucosidase assay and satisfactory results were acquired in real sample determination.