Analytic modelling of biotransistors

The possibility of using devices based on field-effect principles for detecting DNA hybridisation events is an attractive and low-cost alternative to optical reading techniques. Experiments have shown that a change in the threshold voltage of a few millivolts can be attributed to successful hybridisation of targets to probe oligonucleotides tethered on the oxide of a field-effect transistor. Many different phenomena give rise to this voltage shift and some of these phenomena are described. Several justifiable approximations are made to develop an analytic solution of this biosensor that allow for a closed-form expression of the flatband voltage to be derived. Finally, a small-signal model for the BioFET is given, with emphasis on its design and operating conditions for optimum signal-to-noise ratio.