Modeling of Enzyme biosensor based on pH-sensitive field effect transistor for detection of glucose

We develop a physico-chemical model of Enzyme Field effect transistor (ENFET) biosensor for glucose detection by considering some important criteria like biocatalytic reaction, diffusion phenomena and the surface charging of ion sensitive field effect transistor (ISFET). In general, in ENFET creation, though the enzyme is immobilized on the surface of the insulator of the FET device, here we have assumed that the immobilized enzyme molecules have formed an enzymatic layer that behaves as a membrane situated just near the outer Helmholtz plane (OHP). It is essential because the proton generated through enzyme catalyzed reaction must interact with the insulating surface in accordance with the site binding theory which is generally used for ISFET modeling. The concentration of glucose has been characterized by considering two kinds of binding sites in the sensing insulator layer, mainly silanol and basic primary amine sites and the pH dependent electrolyte-insulator potential according to Boltzmann distribution along with the diffusion phenomena of electrolyte substrate. The charges and potentials at the different interfaces are related in accordance with Gouy-Chapman-Stern theory.