Potentiometric and Amperometric Glucose Sensor Using Proton-Conductive Thick-Film

Abstract

New solid-state enzyme sensors capable of potentiometric or amperomet ric detection of glucose were explored based on the proton-conductive thick-film of antimonic acid spin coated on a porous alumina substrate. Two types of planar sensor element were fabricated by depositing the sensing electrode (Pt), counter electrode (Au) and/or reference electrode (Ag) on top of the proton-conductive film by RF sputtering (Figs.1 and 2). Glucose oxidase (GOD)was applied on the Pt electrode together with a carbon paste which not only immobilized GOD but also protected the proton-conductive film from deterioration in the phosphate buffer solution (Fig.4), while the remaining surface was covered with a water-proof coating layer. The two-electrode type element attached with a pair of sensing and counter electrodes worked as a potentiometric sensor which varied emf logarithmically with a change in the concentration of dissolved 02, H₂O₂, and glucose (5 x 10^-4-4 x 10^-2M) in the phosphate buffer solution (Figs.5 and 6). The Nernst's slope (-54 mV/decade) for glucose coincided perfectly with that for H202, indicating that the response to glucose is generated through its enzymatic reaction product, H₂0₂. The sensitivity to glucose was fairly stable for 10 days (Fig.7). The same element could be used as an amperometric sensor when the sensing Pt electrode was polarized vs. an external Saturated Calomel Electrode (SCE) (Fig.8), and the electrolytic current at the fixed polarization of O.7 V (vs. SCE) was well correlated with the glucose concentration (Fig.9). This finding facilitated the design of three-electrode type element by incorporating an internal reference Ag electrode which was inactive to H₂O₂ (Fig.10). The electrolytic current of this element increased as the Pt electrode was polarized vs. the Ag electrode (Figs.11 snf 12), and the amperometric response at the polarization of 0.7 V was linear to the concentrations of H202 and glucose (0-7 x 10^-3M) (Fig.13), with the rather rapid response rates (Fig.14). It was further shown that the short-circuit current of the two-electrode type element could also be utilized for the amperometric detection of dissolved 02, H₂O₂, and glucose (0-4x 10^-3M) in the buffer solution (Figs.15, 16, and 17).