Modified Electrodes from Hydrophobic Alkoxide Silica Gels-lnsertion of Electroactive Compounds and Glucose Oxidase

Silica gels issued either from alkoxides or from colloidal silica are well known to be suitable materials for the immobilization of optically active probes or catalytically active chemicals. Recently it has been demonstrated that an enzyme like glucose oxidase could be immobilized into silica gels and glasses and still was able to retain a part of its activity. Recently, we have demonstrated that gels, either from silica or from transition metals, were appropriate mediums to perform electrochemistry, due to their high content of free solvent. It was a natural development of such studies to prepare modified electrodes from gels. We have developped two kinds of system. On one hand modified electrodes starting from hydrophobic DEDMS/TMMS (dimethoxydimethylsilane and trimethoxymethylsilane in various proportions) gels with small organic electroactive compounds incorporated have been prepared in which the electroactive probe is retained due to the hydrophobic balance of the gel. Such gels are adherent to the electrode and they present the electrochemistry of the electroactive probe included. Different conditions of preparation and drying of the gels are presented in relation with their influence on the behaviour of the modified electrode. On the other hand, glucose oxidase has been incorporated with a water soluble ferrocene as a mediator in silica gels made from colloids (NYACOL), and its catalytic activity has been experienced following the electrochemistry of the ferrocene. The electrochemical response in the presence of glucose is typical of the homogeneous response and the influence of the different parameters, governing the catalysis will be discussed.