Enhancement of bioelectrocatalytic processes by the rotation of mediator-functionalized magnetic particles on electrode surfaces: Comparison with a rotating disk electrode

The rotation of redox-functionalized magnetic particles (MPs) by means of an external magnet is a common practice for enhancing bioelectrocatalytic processes and for the amplification of biosensing events. The current densities generated by rotating redox-functionalized MPs in two bioelectrocatalytic systems are compared to the current densities generated by rotating disc electrodes (RDE) functionalized with similar redox functionalities. The bioelectrocatalytic systems consist of pyrroloquinoline quinone (PQQ)-functionalized MPs that oxidize NADH, and ferrocene-functionalized MPs that mediate the bioelectrocatalyzed oxidation of glucose in the presence of glucose oxidase. The results reveal that only ca. 1% of the area of the redox-functionalized MPs are electrically contacted with the electrode. Also, the current densities generated by the rotating MPs at high rotation speeds are lower than theoretically expected, presumably due to lose of electrical contact between the MPs and the electrode, and incoherent rotation of the particles on the electrode, due to insufficient magnetization. The comparison of the current densities in the bioelectrocatalytic systems in the presence of the rotating redox-functionalized MPs to the analogous RDE systems allows us to elucidate the kinetics of electron transfer at the redox-active MPs.