Effect of screening on the sensitivity of field-effect devices used to detect oligonucleotides

The effect of screening and the establishment of the Donnan potential at the floating gate of field-effect transistors (BioFETs) are calculated for a model that includes proton site binding on metal oxides used as gate insulators. Variations of response with pH, electrolyte concentration, and the fixed charge density of oligonucleotides are calculated assuming the charge is distributed homogenously in an ion-permeable membrane of finite thickness. Derived expressions describe the change in threshold voltage with electrolyte concentration and pH. These could be used to predict the sensitivity of the BioFET to hybridization, and provide a means of calibration prior to use. (c) 2008 American Institute of Physics.