Potentiometric thick-film sensor for the determination of the neurotransmitter acetylcholine

A potentiometric thick-film biosensor for the determination of the neurotransmitter acetylcholine is presented. The selective membranes consist of two layers. The first is a choline- and H(+)-selective membrane made from a poly(vinyl chloride)-poly(vinyl acetate) copolymer which is plasticized with 2-nitrophenyl octyl ether. It contains 1% m/m of the ion-pair choline phosphotungstate as an electroactive compound. Both products of the enzymic cleavage, choline and H+, are detected. The second layer is placed above the first and is made from a poly(vinyl acetate)-polyethylene dispersion polymer. It is loaded with 2% m/m of acetylcholinesterase isolated from electric eel. The linear region of the response curve extends from 2 x 10(-5) to 0.01 mol dm-3 in buffer solution and undiluted horse serum. The detection limit is 5 x 10(-6) mol dm-3 and the response time is about 4 min.