Sensitivity of field-effect biosensors to charge, pH, and ion concentration in a membrane model

In field-effect transistors used to detect charged biomolecules (BioFETs), the biomolecules form a charged membrane on the transistor surface. In this paper, the one-dimensional Poisson–Boltzmann equation is used to calculate the charge sensitivity (the sensitivity of the BioFET to changes in biomolecule charge), ion sensitivity (to changes in ion concentration of the solution), or pH sensitivity (to changes in pH of the solution), both analytically and numerically, and the results are compared to models where the charged molecules are represented as an infinitely thin plane. Complexation of ions with the oxide surface is shown to have a negligible effect on parameters typical of devices, but the layer used to tether the charged molecules to the surface could modify the sensitivity considerably.