Redox reactions with soluble ferrocenes

The reaction scheme used in the first commercial electrochemical test strip from MediSense (now Abbott Diabetes Care) is shown later. Electron transfer rates between the reduced form of glucose oxidase and ferricinium ion derivatives are very rapid compared with the unwanted side reaction with oxygen (Cass et al. 1984 Forrow et al. 2002). The Abbott Diabetes Care Precision QID strip includes the l,l -dimethyl-3-(2-amino-l-hydroxyethyl) ferrocene mediator, which has the desirable characteristics of high solubility in water, fast electron-shuttling (bimolecular rate constant of 4.3 X 10 M s ), stability, and pH independence of the redox potential (Heller and Feldman 2008). Electrochemical oxidation of the ferrocene derivative is performed at 0.6 V. Oxidation of interferences, such as ascorbic acid and acetaminophen present in blood, are corrected for by measuring the current at a second electrode on the strip that does not contain glucose oxidase. 

The majority of these problems have been overcome by the use of ferrocene derivatives as electron acceptors for soluble oxidases (e.g. GOx). Ferrocene derivatives of varying charge and solubility, with redox potentials (E ) between -1-0.1 V and -1-0.4 V, have been shown to accept electrons from GOx [30]. The published values [22] for the second-order rate constant ( em) for the reaction of the reduced active center of GOx (FADH2) and an oxidized ferrocene derivative range from 0.26 x 10 to 5.25 X 10 There is no simple... 

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