Colorimetric assay of butyrylcholinesterase activity based on para-sulfonatocalix[4]arene-modified gold nanoparticles

A novel colorimetric method has been developed for butyrylcholinesterase (BChE) assay and screening of its inhibitors based on para-sulfonatocalix[4]arene-modified gold nanoparticles (pSC4-AuNPs). The host–guest interaction between succinylcholine (SuCh, substrate of BChE) and two pSC4-AuNPs result in pSC4-AuNPs tending to aggregate. However, the hydrolyzed product of choline (Ch) has no coordination reactivity with pSC4. Therefore, owing to the hydrolysis of BChE, the aggregation of pSC4-AuNPs will be influenced by BChE activity. A simple colorimetric method for the assay of BChE activity can be developed. Under the optimized experimental conditions, the ratios of absorbance at a wavelength of 700 nm to that at 528 nm vary linearly with the BChE activity in the range from 0.05 to 0.25 U mL−1 with the lowest detection limit of 0.0068 U mL−1, providing a new tool for the direct measurement of BChE. Moreover, using this proposed method, the inhibition effect of Tacrine on BChE activity can be tested with IC50 values of 220 μM. This method has great potential not only for the detection of BChE activity but also for the screening of the inhibitors.