Recently, we have succeeded in developing stable and long-term operation of an extended-gate field effect transistor-type glucose sensor using a silk-fibroin film for the immobilization membrane of glucose oxidase. In this paper, we report the fabrication process and characterization of the fibroin film. High-purity silk fibroin powder was used as the solute material in water. The advantage of this material is high solubility in water, non-toxicity to human body, and capability of stable immobilization of enzyme molecules. The fibroin film was formed on a glass substrate using a spin coating method followed by an insolubilation treatment in 80 wt% ethanol aqueous solution. It was revealed that the bond strength between the film and the substrate was dramatically improved by applying a silane coupling treatment to the substrate. The obtained film showed β-sheet structure and contained dense nanopores on the surface.
