Mediator-based glucose biosensors

FIGURE 3.2 Sequence of events that occur in second-generation (mediator-based) glucose biosensor mediated systems. 

Alonso et al. prepared ferrocenyl silicon dendrimers [67], which could be used as mediators in glucose biosensors, based on glucose oxidase [68, 69], The ferrocenyl units are located at the end of long, flexible, silicon containing branches and serve to electrically connect the enzyme to the electrode. The flexibility of the dendrimer is proposed to play an important role in the interaction with the redox center of glucose oxidase. 

Z. Gao, F. Xie, M. Shariff, M. Arshad and J.Y. Ying, A disposable glucose biosensor based on diffusional mediator dispersed in nanoparticulate membrane on screen-printed carbon electrode, Sens. Actuators B Chem., 111-112 (2005) 339-346. 

For this reason, in the last decade, inorganic electrochemical mediators, which catalyse the oxidation or reduction of H202 have been preferred to HRP and have been used for the assembling of oxidase-based biosensors [18-20]. This results in a decrease of the applied potential and the consequent avoidance of electrochemical interferences. Many electrochemical mediators have been used and many of them have found broad application, especially in glucose biosensors for diabetes control. However, due to the solubility of the mediator, they are generally employed in a single-use sensor and present some problems due to the low operative stability. 

The discussion of sensors, especially those used for continuous monitoring, will be based on biosensors using glucose oxidase with electrochemical detection. The sensors generally adhere to the following sequence of reactions of enzyme, E, and mediator, M ... 

This enzyme-based biosensor uses glucose oxidase (GO) as a chemical recognition element, and an amperometric graphite foil electrode as the transducer. It differs from the first reported glucose biosensor discussed in the introduction to this chapter in that a mediator, 1,1 -dimethylferricinium, replaces molecular oxygen as the oxidant that regenerates active enzyme. The enzymatic reaction is given in Eq. 7.15, and the electrochemical reaction that provides the measured current is shown in Eq. 7.16. 

Pravda, M., Adeyoju, O., Iwuoha, E.I., Vos, J.G., Smyth, M.R., and Vytfas, K. (1995) Amperometric glucose biosensors based on an osmium(2-l-/3-l-) redox polymer-mediated electron transfer at carbon paste electrodes. Electroanalysis, 7, 619-625. 

The outstanding properties of PB-modified electrodes in H2O2 detection have made this device a very good candidate for the development of oxidase-based amperometric biosensors. Among the different analytes proposed, the determination of glucose by the mediation of glucose oxidase stUl remains the primary application of PB-modified electrodes, even in a real context [52]. 

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