BIOELECTROCATALYSIS AND DIFFUSION KINETICS OF THE GLUCOSE-OXIDASE - GLUCOSE REACTION USING A WATER-SOLUBLE 1,1'-DIMETHYLFERROCENE-2-HYDROXYPROPYL-BETA-CYCLODEXTRIN COMPLEX

The mediation of the glucose oxidase (GOx): glucose reaction by 1,1'-dimethylferrocene (DMF) solubilized in 2-hydroxypropyl-beta-cyclodextrin (hpbetaCD) was studied. Cyclic voltammetry (CV) was used to examine the effects of complexation with hpbetaCD on the oxidation potential of DMF through the analysis of half-wave potentials. This indicated a one-to-one complex between DMF and hpbetaCD;, with a formation constant of (1.2 =/- 0.3) x 10(3) M-1. The working potential for electrodes using the mediator complex could be reduced by minimizing the hpbetaCD concentration, though a lower limit of 2.5 mM was observed for the 0.5 mM DMF solutions used in this work, below which the DMF became insoluble, and its electrochemistry was not well behaved. Cyclic voltammetry measurements at different scan rates were used to determine kinetic parameters, resulting in a second-order rate constant for the reaction of oxidized DMF with reduced GOx of 3.4 x 10(4) M-1 S-1 to 1.9 X 10(4) M-1 s-1 for solutions containing 4 mM to 10 mM hpbetaCD. These values are on the order of one-quarter the literature value for free DMF and are in the range reported for ferrocene, indicating that the complexed DMF is able to function as an efficient mediator. The rate constant determined for 2.5 mM hpbetaCD was anomalously high and probably indicated insolubility of the DMF at this hpbetaCD concentration. A rate constant versus the hpbetaCD concentration plot was used as an indication of the lower limit of hpbetaCD concentration at which reproducible results could be obtained.