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A biosensor for glucose utilizing kinetics of glucose oxidase (EC 1.1.3.4.) was developed. The enzyme was immobilized on polyaniline by covalent bonding, using glutaraldehyde as a bifunctional agent. The system showed a linear response up to 2.2 mM of glucose with a response time of 2.5-4.0 min. In addition, the immobilized enzyme had a higher activity between pH 6.5 and 7.5. The system retained 50% of its activity after 30 d of daily use. The optical absorption spectra of the polyaniline/glucose oxidase electrode after glucose had been added to the buffer solution showed that the absorption band around 800 nm had changed considerably when glucose was allowed to react with the electrode. This optical variation makes polyaniline a very promising polymer for use as a support in optical sensor for clinical application.

A biosensor for ascorbic acid based on enzyme kinetics of ascorbate oxidase (E.C.1.10.3.3) was developed. The enzyme was extracted from Cucurbita maxima, or jerimun and immobilized by covalent bounding, using glutaradehyde as a bifunctional agent, on alkylamine glass beads, with and without enzyme active site protection. A low-cost, home-made oxygen electrode was applied as a transducer. The system has sensitivity from 62.5 up to 500 microM of ascorbic acid with satisfactory operation for more than 2 mo.