Supercritical carbon dioxide immobilization of glucose oxidase on polyurethane/polypyrrole composite

Glucose oxidase (GOX) was immobilized on polyurethane/polypyrrole (PU/PPY) composite foam via supercritical fluid immobilization (SFI) towards the preparation of biosensors. Buffer solution was used as the immobilization medium along with scCO2. To provide insight into the relation between the scCO2 and the GOX-buffer solution, the GOX-buffer solutions were subjected to scCO2 and the protein amounts of the GOX-buffer solutions before and after scCO2 exposure were determined at 80, 100 and 150 bar and 30, 40 and 50 °C for an exposure time of 24 h. The protein amount in GOX-buffer solution decreased in all cases after exposure to scCO2. The lowest and highest loss in GOX amounts observed were 2.9 and 36.4 μg at 80 bar, 30 °C and 100 bar, 50 °C, respectively. The effects of immobilization pressure (80, 100 and 150 bar), temperature (30, 40 and 50 °C) and time (4, 24 and 72 h) on the activities of the GOX-immobilized PU/PPY composites were investigated. At 30 °C immobilization temperature, the activity values of the GOX-immobilized PU/PPY composites were slightly increased as the pressure was increased from 80 to 100 bar. Further increase in immobilization pressure from 100 to 150 bar at 30 °C caused a decrease in the activity values. At 40 °C immobilization temperature, increasing the immobilization pressure from 80 to 100 bar did not provide an increase in activity values, but further increase to 150 bar caused a decrease in the activity values. At 100 bar immobilization pressure, decrease in temperature enhanced the activity values of the samples. When immobilization was performed via SFI, the activity values were doubled compared to the immobilization at atmospheric conditions. Among all the immobilization pressures and temperatures investigated, both the highest activity (U/cm2) and the highest specific activity (U/mg) were obtained for the samples processed at 100 bar, 30 °C.