Rapid and highly-sensitive determination of acetylcholinesterase activity based on the potential-dependent adsorption of thiocholine on silver electrodes

A method of adsorptive stripping voltammetry has successfully been applied to the highly-sensitive determination of acetylcholinesterase (AChE) activity. Thiocholine, which was produced through the AChE-catalyzed hydrolysis of acetylthiocholine, chemisorbed on a silver electrode surface during an incubation time; then, the silver electrode was transferred into an alkaline solution, and the adsorbent was electrochemically desorbed by the reductive desorption. A cathodic peak for reductive desorption became larger in association with the increase of the AChE activity. The lower detection limit obtained with the incubation time for 30 min was 0.01 U l−1, which was 100-fold higher than that was obtained by a conventional amperometric sensor. The chemisorption rate of the thiocholine molecules on the silver surface was increased by applying a negative potential, owing to the electrostatic interaction between the positively changed thiocholine and the negatively charged silver surface. This led us to determine AChE with a reduced incubation time. The AChE activity 0.01 U l−1 could be determined with the incubation time as short as 5 min, when a negative potential of −0.7 V (vs. Ag/AgCl) was applied to the silver surface.