IMPROVEMENT OF ELECTROCHEMICAL BIOSENSORS USING ENZYME IMMOBILIZATIONFROM WATER-ORGANIC MIXTURES WITH A HIGH CONTENT OF ORGANIC-SOLVENT

We propose immobilizing enzymes into Nafion mem membranes by suspendin g the enzyme in a water-ethanol mixture with a high (> 90%) ethanol co ntent, followed by mixing with the dissolved polyelectrolyte, and fina lly allowing the enzyme-polyelectrolyte solution to dry at the target surface (electrode surface). Since Nafion solution was deposited from a solution where it is truly dissolved and without excessive dilution with water, the resulting membranes were more uniform and stable than those otherwise obtained. Enzyme suspensions in concentrated ethanol s olutions were prepared without any prior modifications of the protein. The remaining activity after 30 min exposure to such solutions under optimal conditions was up to 100%. The stability of the enzymes in the se suspensions was higher than that in aqueous solution. Electrochemic al biosensors made accordingly showed a several times increased respon se compared with those of enzyme electrodes based on the traditional w ay of using excessive dilution of Nafion with water. The remaining act ivity, after the drying-washing cycle of the enzyme electrode made by enzyme immobilization from concentrated organic solvent, was at least 10 times higher thats that of the traditional one.