The characteristics of a glucose sensor based on an ion-sensitive TiO2/Ti extended gate electrode field-effect transistor (EGFET) are reported. A glucose oxidase-containing silk fibroin membrane was immobilized on a TiO2/Ti surface as the bio-sensing component. This EGFET-type biosensor was estimated to be able to detect a glucose concentration as low as 0.001 mg/mL in an aqueous electrolyte, which enables the sensing of glucose in the saliva and sweat. The endurance of this sensor was also examined, and it was found that the retention time of the original sensitivity for repeated use at room temperature was more than 30 days, with a high heat tolerance temperature close to 60 °C.

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 -sheet structure and contained dense nanopores on the surface.