Modeling of fluctuation processes on the biochemically sensorial surface of silicon nanowire field-effect transistors

Affinity-type silicon-based nanowire biosensors rely on the biochemical interaction between target molecules and their molecular complements (recognition probes), located on the SiO2 insulator layer. This biochemical reaction is associated with twofold fluctuations through the mechanisms of binding/unbinding and regular charge thermal equilibrium processes. These fluctuations have a direct implication on the surface potential fluctuations which in turn affect, through the field effect transduction process, the electrical characteristics of the sensor device. The resulting noise could potentially contain detectable information, which can be extracted through the time constants (characteristic frequencies) related to the kinetics of the molecules under detection and their charge fluctuations. In this work, we present a comprehensive model for the fluctuations on the surface of the biosensor and attribute them to the two physical mechanisms. The spectral densities corresponding to these types of fluctuations add on the overall device noise spectrum and are directly detectable if they lie above the inherent noise level of the sensor device. (C) 2015 AIP Publishing LLC.