Polyvinylferrocenium immobilized enzyme electrode for choline analysis

The response characteristics of a new enzyme electrode for determining choline are reported. The enzyme electrode consists of a polyvinylferrocenium perchlorate coated Pt surface onto which the enzyme, choline oxidase, is attached. Choline oxidase catalyzes the oxidation of choline to betaine, producing H2O2. Current due to H2O2 oxidation catalyzed by polyvinylferrocenium centers was measured. The effects of choline concentration, the amount of enzyme immobilized and the operating pH and temperature on the response of the enzyme electrode were studied. The effects of interferents were also investigated. The response time was found to be 60–70 s and the upper limit of the linear working portion was found to be 1.2 mM choline concentration. The minimum substrate concentration that produced detectable current was 4.0×10−6 M choline concentration. The steady-state current of this enzyme electrode was reproducible within ±4.6% of relative error. The apparent Michaelis–Menten constant (KMapp) and the activation energy, Ea, of this immobilized enzyme system were found to be 2.32 mM and 38.91 kJ/mol, respectively.