3 years ago

Off-on-off detection of the activity of acetylcholine esterase and its inhibitors using MoOx quantum dots as a photoluminescent probe

Zhao Jun Chu, Sai Jin Xiao, Zhi Bin Zhang, Xiao Jing Zhao, Yun Hai Liu

Abstract

The authors describe a fluorometric "off-on-off" method for the determination of the activity of acetylcholine esterase (AChE). Molybdenum oxide quantum dots (QDs) are used as a fluorescent probe having excitation/emission peaks at 405/525 nm. It is found that the photoluminescence of such QDs is quenched by Cu(II) ion but that it can be restored by acetylcholine which is formed by AChE-catalyzed hydrolysis of acetylthiocholine. The effect is due to the strong affinity between Cu(II) and the thiol group of acetylthiocholine. Hence, quenching is increasingly reversed with increasing concentrations of AChE. However, fluorescence is not restored if the activity of AChE is inhibited by an inhibitor. Under optimal conditions, a linear relationship is founded in the 0.05 to 15 mU·mL−1 AChE activity range, with a limit of detection of 35 μU·mL−1 (applying the 3σ/k criterion). Three organophosphate pesticides and propazine were used to validate the assay. All showed strong inhibition, with IC 50 values (the concentration required for 50% inhibition to occur) to be 52, 221, 48 and 9 nM for diazinon, chlorpyriphos, monocrotophos and propazine. Benefitting from its sensitivity, specificity and simplicity, the assay in our perception provides a valuable tool for detection of AChE activity and in screening for its inhibitors.

Graphical abstract

A novel “off-on-off” assay is constructed for acetylcholine esterase (AChE) activity and inhibitor screening benefitting from the phenomenon that the photoluminescence of molybdenum oxide quantum dots (MoOx QDs) is quenched by Cu2+ and that the quenched photoluminescence can be restored due the strong affinity between Cu2+ and thiocholine (Tch) which is the hydrolysis product formed due to catalysis by AChE.

Publisher URL: https://link.springer.com/article/10.1007/s00604-017-2519-2

DOI: 10.1007/s00604-017-2519-2

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