A colorimetric assay for acetylcholinesterase activity and inhibitor screening based on the thiocholine-induced inhibition of the oxidative power of MnO2 nanosheets on 3,3,5,5-tetramethylbenzidine

The authors describe a colorimetric method for the determination of the activity of acetylcholinesterase (AChE). Manganese dioxide (MnO2) nanosheets directly reacts with 3,3,5,5-tetramethylbenzidine (TMB) in the absence of hydrogen peroxide (H2O2). This leads to the formation of a blue product (oxTMB) with an absorption peak at 652nm. If AChE hydrolyzes its substrate acetylthiocholine chloride, thiocholine is formed which blocks the oxidative power of the MnO2 nanosheets. Hence, oxTMB will not be formed. The decreased absorbance is directly related to the AChE activity in the 0.01-1.0mU mL(-1) range. The detection limit is 0.01mUmL(-1) and the relative standard deviation is 1.2% (for n=11 at 0.5mUmL(-1)). The method was also applied to screen for inhibitors of AChE.