Oxidase-mimicking activity of ultrathin MnO 2 nanosheets in colorimetric assay of acetylcholinesterase activity

In the present study, a novel colorimetric sensing platform was constructed for quantitative detection of acetylcholinesterase (AChE) activity and its inhibitor. Manganese dioxide (MnO2) nanosheets as an oxidase-mimicking nanomaterial could directly oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) into oxTMB without the need for horseradish peroxidase and H2O2. When AChE was introduced, acetylthiocholine could be catalytically hydrolyzed to produce thiocholine, which easily triggers the decomposition of MnO2 nanosheets, causing the decrease of solution absorbance. Owing to the inhibition effect of organophosphorus pesticides, the enzymatic activity was suppressed, preventing the decomposition of MnO2 and resulting in the increase of absorbance. Under optimal conditions, the colorimetric platform shows sensitive responses to AChE and paraoxon in the range of 0.1–15 mU mL−1 and 0.001–0.1 μg mL−1, respectively. The detection limits of AChE and paraoxon reached 35 μU mL−1 and 1.0 ng mL−1, respectively. Furthermore, the MnO2-TMB platform has been used to fabricate test strips for rapid and convenient visual detection of AChE and its inhibitor with highly promising performance.