BIOSENSOR PROPERTIES OF GLUCOSE-OXIDASE IMMOBILIZED WITHIN SIO2 GELS

The sol-gel immobilization of enzymes within metal oxides results in t hin composite layers which are useful for biosensors, e.g., in combina tion with optical or electrochemical transducers. The activity of gluc ose oxidase (GOD) immobilized within SiO2 gels is mainly determined by the chemical and physical parameters of the sol-gel process. So, the type of the sol, the conditions of the SiO2 formation, the GOD concent ration and the addition of penetration agents are studied to optimize the enzyme activity and the response of the complete amperometric bios ensors. Both optical and electrochemical methods are used to measure a ctivities of immobilized GOD. The applications of such GOD-SiO2 compos ites (i) directly on the electrode surface of a flat sensor, (ii) indi rectly within Cuprophan(R) membranes of an amperometric hydrogen perox ide sensor or (iii) on zeolite beads in a cartridge followed by an H2O 2 sensor are compared with regard to sensitivity and selectivity of th e respective sensor systems. The best membrane sensor properties are o btained for silica hydrogel composites containing large amounts of GOD produced with sols from acidic hydrolysis of a 25% 3-aminopropyltrime thoxysilane-75% tetraethoxysilane precursor. Xerogels from acidic hydr olysed tetraethoxysilane sols within aprotic solvents like dioxane are favoured for direct application on Pt working electrodes of flat sens or structures.