Assay of acetylcholinesterase activity by potentiometric monitoring of acetylcholine

An acetylcholine-selective electrode based on a plasticized polymeric membrane has been developed. The electrode exhibited good selectivity for acetylcholine (ACh) over choline and some common ions, low drift, and a fast response to ACh. The response was linear over an ACh concentration range of 1 × 10−6 to 1 × 10−3 M with a slope of 59.1 ± 0.1 and a detection limit of 1.5 × 10−7 ± 1.2 × 10−8 M. The electrode was used to monitor enzymatic ACh hydrolysis catalyzed by acetylcholinesterase (AChE) at different substrate and enzyme concentrations. A kinetic data analysis permitted the determination of the Michaelis–Menten constant of the enzymatic hydrolysis and AChE activity in the range of 2 × 10−5 to 3.8 × 10−1 U ml−1.