ELECTROCHEMICAL GLUCOSE SENSORS ON PERMSELECTIVE NONCONDUCTING SUBSTITUTED PYRROLE POLYMERS

Our aim has been to construct biosensors which can be produced in large numbers for commercial use with high stability and selectivity. Thin-film technology is able to provide the high purity and reproducibility required of the electrode surface and the high spatial resolution of the electrode structure. A four-electrode electrochemical cell with an outer diameter of 2.5 mm possessing two identical working electrodes is produced by using glass sheets or Upilex foils as electrode carriers. These sheets, coated with thin titanium layers acting as an adhesion layer, are covered with platinum to form an electrochemical electrode. After structuring, the conducting lines are isolated by silicon nitride or polyimide. To coat the platinum electrodes with polymeric layers new strategies in the synthesis of 1- and 3-substituted pyrroles have been developed to obtain 1-(carboxyalkyl) pyrroles, 2-(1-pyrrolo)-acetylglycine, 1-alkylpyrroles, 1-(4-carboxybenzyl)-pyrrole, 1-(4-nitrophenyl) pyrrole, 4-(3-pyrrolo)-4-ketobutyric acid and 3-((keto 4-nitrophenyl) methyl) pyrrole as monomers. New types of polymer-coated electrodes are prepared and characterized further by electrochemical oxidation and polymerization of these monomers in organic solvents. To couple enzymes and to activate terminal carboxy and nitro groups of the polymer, water-soluble carbodiimides and chloranil are found to give the best results. The activated electrodes are reacted immediately with glucose oxidase and the glucose sensors thus obtained are stored at 4-degrees-C. Electrodes covered by substituted polypyrrole layers having no redox activity show two fundamental advantages: a significant increase of response per unit area due to the porous polymer and permeation control for interfering electroactive substances by the polymeric layer, resulting in a distinct increase in selectivity.