FUNCTIONAL LANGMUIR FILMS WITH GLUCOSE-OXIDASE

Adsorbed layers of glucose oxidase on an air-water interface were prepared and investigated. The enzyme is more strongly adsorbed on positively charged lipid monolayers than on zwitterionic ones and only slightly adsorbed on negatively charged monolayers of stearic acid, probably because of the total negative charge of the protein molecule in buffer solution at pH 7.0. It is found that the amount of protein at the air-water interface is two times higher than in the subphase solution and that glucose oxidase retains its enzymatic activity in adsorbed layers. The transfer of between one and ten lipid-protein monolayers onto Pt electrodes under 20-40 mN m-1 surface pressure by the Langmuir-Blodgett method was performed. As a result the biosensor was obtained with a measuring range of 0.5-5.0 mM glucose. The best electrode characteristics were found with glucose oxidase adsorbed on mixed monolayers of phosphatidylcholine/cetyltrimethylammonium bromide. The amperometric response was found to depend on the number of transferred lipid-protein monolayers and on the surface pressure at which the transfer was carried out.