A fluorometric assay for acetylcholinesterase activity and inhibitor screening with carbon quantum dots

This report presents a convenient and reliable fluorometric assay for acetylcholinesterase (AChE) activity and inhibitor screening by taking carbon quantum dots (CQDs) as the signal reporter. The detection mechanism is based on the following facts: (1) the aggregation of CQDs by copper (II) ions results in its fluorescence quenching due to strong coordination of copper ions to carboxyl groups of CQDs; (2) AChE can catalyze the hydrolysis of acetylthiocholine into thiocholine which can induce fluorescence recovery owing to stronger affinity between thiocholine and copper ions; (3) when its inhibitor tacrine is present, AChE loses its catalytic ability for hydrolysis of acetylthiocholine, and thus the fluorescence remains quenched. With this convenient method, the activity of AChE with a concentration as low as 4.25   U/L and a broad linear scope ranging from 14.2 to 121.8   U/L can be assayed, which possesses adequate sensitivity for practical samples of human serum and seminal plasma. The promising application of the proposed method in AChE inhibitor screening was demonstrated. This work expands the application of carbon quantum dots in biological analysis, and provides a new fluorescent assay for AChE activity monitoring and AChE inhibitor screening using a cheaper fluorescent material.