Glucose oxidase immobilization on conducting polymers in supercritical CO2 environment: An exploratory study

Glucose oxidase (GOX) is immobilized on two conducting polymers: polypyrrole (PPY) film and polyurethane/polypyrrole (PU/PPY) composite foam, via supercritical fluid immobilization (SFI) for use in the preparation of biosensors. The effects of supercritical carbon dioxide (scCO2) (80–150 bar, 40 °C) and temperature (30–60 °C) on free-enzyme buffer-solution activity are investigated for 24 h scCO2 exposure time. Results show that enzymatic activity of GOX after exposure to scCO2 is retained. The enzymatic activity of GOX-buffer solution does not show a noticeable decrease between 30 and 50 °C, whereas 30 and 94% activity losses are noticed at 55 and 60 °C temperatures. The GOX immobilized PPY films and PU/PPY composite foams are analyzed via environmental scanning electron microscopy (ESEM) and enzymatic activity methods. Four different immobilization mediums are used for PPY films: dry GOX and dry PPY (Dry); dry GOX and dry PPY with water vapor (Semi-Dry); GOX and PPY in water (Wet); GOX and PPY in buffer (Wet-b). In “Dry” and “Semi-Dry” procedures (up to 150 bar, 40 °C and 72 h), the PPY films showed no noticeable activity, whereas films processed in “Wet” and “Wet-b” methods showed enzymatic activity. In “Wet” method (150 bar and 40 °C), as the immobilization time increased (5–72 h) the activity was enhanced. The maximum activity is observed for GOX immobilized PPY in the “Wet-b” medium. Thus, during GOX immobilization of PU/PPY, buffer solution is used as the immobilization medium. Experiments are conducted at 40 °C and for 24 h. The immobilization pressure effect (75–150 bar) on the activities of GOX-immobilized PU/PPY composites are investigated. Activity of the immobilized enzyme increases significantly from 75 to 105 bar. Further pressure increase to 150 bar causes a decrease in the activity of the GOX-immobilized PU/PPY composite sample. Immobilization of GOX onto PU/PPY composite at 1 bar is not found feasible.