Inert metal-modified, composite ceramic-carbon, amperometric biosensors:  renewable, controlled reactive layer.

A new type of sol-gel-derived, inert metal-modified, composite, amperometric biosensor is developed. The electrodes are comprised of a dispersion of biochemically and chemically modified graphite powder in a porous, organically modified silicate (Ormosil) network. The percolating carbon dispersion provides electrical conductivity, oxidoreductase enzymes (e.g., glucose oxidase, lactate oxidase, or l-amino acid oxidase) are used for biocatalysis, metallic palladium is used for electrocatalysis of the biochemical reaction product, and the porous organically modified silica provides a rigid skeleton. The hydrophobicity of this composite material guarantees that only a limited section of the electrode is wetted by the aqueous analyte, thus providing a controlled-thickness reactive layer. The thickness of the reaction layer can be tuned by the addition of hydrophilic components. The electrode can be reproducibly renewed by removing its upper layer and exposing a new, thin, porous bioreactive section. The same technology is applicable for the production of thick-film, low-leaching, disposable sensors. In this configuration, the analysis is conducted using a single drop of the analyte applied on the hydrophobic film. The sensors are found to be stable over long periods.