Journal of Sol-Gel Science and Technology 7, 123-128 (1996) @ 1996 Kluwer Academic Publishers. Manufactured in The Netherlands. Sol-Gel Derived Ceramic-Carbon Enzyme Electrodes: Glucose Oxidase as a Test Case SRINIVASAN SAMPATH, IRENA PANKRATOV, JENNY GUN AND OVADIA LEV Division of Environmental Sciences, School of Applied Science, The Hebrew Universig of Jerusalem, Jerusalem, 91904, Israel Received July 5, 1995; Accepted October 31, 1995 Abstract. Several types of amperometric biosensors comprised of immobilized glucose oxidase in chemically- modified ceramic-carbon matrices are compared. The electrodes are comprised of several building blocks each performing a specific function. Glucose oxidase is used to catalyze the bio-oxidation of glucose; carbon powder imparts conductivity and favorable electrochemical characteristics: the Ormosil network provides rigidity and porosity; and the organic modification of the Ormosil imparts controlled surface polarity. Additionally, hydrophilic chemical modifiers are incorporated in order to control the size of the wetted, electroactive layer; high dispersion of inert metal catalysts is used to enhance hydrogen peroxide oxidation and redox mediators may be co-immobilized when oxygen independent response is desirable. The electrodes can be prepared either in the form of thick supported film, useful for disposable electrodes or as bulk-modified, disk shape electrodes, which can be used as renewable surface electrodes. Keywords: sol-gel, biosensor, electrode, glucose oxidase 1. Introduction The pioneering work of Braun et al. [ 11, demonstrating sol-gel doped xerogels triggered an extensive research in bioceramics, yielding also a large number of sol-gel derived biosensing applications [2-4]. Most of the ac- tivity in this field was directed to the development of photometric applications, due to the favorable optical characteristics of silica and organically modified silica (Ormosil) matrices [5-71. However, the versatility of the sol-gel processing makes it also a most promising route for the production of silica and silica compos- ite electrochemical devices. Indeed, several research groups have reported sol-gel derived electrochemical applications, including films of wet silica gels on inert metal electrodes [ 81, doped silica powders attached by a plastic membrane to a Clark oxygen electrode [9], and sandwich type electrodes, in which the enzyme is immobilized between two layers of sol-gel derived sil- ica [lo]. Kurokawa and coworkers used enzyme doped composite titania-cellulose biofilm electrodes [ 111 and we have concentrated on the development of conduc- tive matrices such as vanadium pentoxide gels [ 121 and composite carbon-silica matrices [ 13, 141. This paper summarizes the activities of our group on the development of composite carbon-ceramic biosen- sors. Using the welldocumented [8-10,12-171 glucose oxidase enzyme as a common test case, we demon- strate how sol-gel processing can be used to tailor dif- ferent types of composite, organically modified silica- carbon electrodes. We shall refrain from extensive dis- cussion of the metrological characteristics of each class of biosensors and instead present an overview of dif- ferent pathways that demonstrate the power of sol-gel technology. 2. Ceramic-Carbon Electrodes (CCEs) Ceramic-carbon electrodes are made of a dispersion of l-40% (w) carbon powder in porous, organically modified silica support [18, 191. Typical preparation procedure of these electrodes is as follows. 1.5 ml