Enzyme microelectrodes for choline and acetylcholine and their applications

Hydrogen peroxide based amperometric microsensors have been developed for choline (Ch) and acetylcholine (Ach) by coimmobilization of acetylcholinesterase (AchE) and choline oxidase (ChO) on platinum disk microelectrodes using glutaraldehyde vapor. The sensor was applied in micro flow injection and micro liquid chromatographic analyses. The chromatographic peak heights were linearly proportional to the amounts of Ach and Ch over the range of 0.05 to 103 pmol (8 × 10−7 to 1.5 × 10−2 M, 0.06 μl) with correlation coefficients > 0.99. Immobilization of ChO was used for the selective determination of Ch with a response time of 5 s. This electrode was used for activity measurements of AchE down to 0.25 U ml−1 in a 1 μl volume in a batch method at a total volume of 5.0 ml.