DEVELOPMENT OF AMPEROMETRIC SENSORS FOR CHOLINE, ACETYLCHOLINE AND ARSENOCHOLINE

Immobilisation of acetylcholine esterase (ACE) and choline oxidase (COx) within a polymeric coating on a glassy carbon electrode resulted in the development of a sensor for the important transmitter acetylcholine and its metabolite choline. Anodic detection at +0.25 V vs. SCE is facilitated by the addition of the redox-mediating hexacyanoferrate(III) ion. The influence of various experimental parameters is described. Linearity for acetylcholine and choline responses extended up to 5 mM and 13 mM, with limits of detection of 43 muM and 50 muM, respectively. The simple immobilisation procedure and the rapid reaction kinetics between the mediator and the enzyme, coupled to a fast heterogeneous rate constant, resulted in rapid response times and good precision. An important application of the biosensor was shown for the determination of arsenocholine, using the choline oxidase immobilised electrode, resulting in a response ten times that obtained for choline, with linearity extending up to 0.6 mM and a limit of detection of 10 muM. The high selectivity offered by this sensor was indicated by the lack of interference offered by easily oxidised compounds normally found in serum, because of both the charge exclusion properties of the Nation polymeric coating and the low operating potential required to re-oxidise the mediator.