Impedance Modelling of FET-Based Biosensors

In designing microfabricated electrodes or field-effect DNA biosensors, the response to the oligonucleotides is often quantified in terms of static changes in the sensed current or potential. More recently, changes to the AC impedance of the device have been used for a variety of reasons. We present here a small-signal, physics-based AC model for biological Field-Effect Transistors (BioFETs), used for detecting DNA molecules. Our model includes the kinetics of the ions in the electrolyte, as well as the electrons and holes in the semiconductor. Using finite-element analysis, we are able to model impedance changes in BioFET structures. Such a model can be used as a quantitative indicator for DNA hybridization experiments.