Fumio Mizutani

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

Abstract 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 30xa0min was 0.01xa0Uxa0l −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 0.01xa0Uxa0l −1 could be determined with the incubation time as short as 5xa0min, when a negative potential of −0.7xa0V (vs. Ag/AgCl) was applied to the silver surface.

Surface potential imaging of organic and biological samples by using scanning Maxwell-stress microscopy (SMM)

Surface potential measurement on organic thin films and isolated biological samples have been performed using a scanning Maxwell-stress microscopy (SMM). The SMM is a type of scanning probe microscopy designed to image microscopic electrical properties, such as the local surface potential distribution. The present microscope afforded information of the lateral distribution of molecular dipole moments in phase separated monolayer, and the topographic image of purple membrane fragments as well as dielectric properties of samples.