Limits of detection for silicon nanowire BioFETs

Over the past decade, silicon nanowire/nanoribbon field-effect transistors (NWFETs) have demonstrated phenomenal sensitivity to the detection of biomolecular species, with limits of detection (LOD) down to femtomolar concentrations [1].However, a fundamental understanding of these limits has been lacking until now. Several well known factors limit the LOD; among them, ionic concentration, efficiency of the biomolecule-specific surface functionalization, binding constants, and the delivery of the analyte to the sensor surface. However, the signal-to-noise ratio (SNR) of these bioFET sensors, and the device parameters that determine the LOD, are not well understood. For example, it has been commonly claimed [2] that NWFET sensitivity is maximized in the subthreshold operating regime of the device. We show here, contrary to this claim, that the SNR is maximized at maximum transconductance due to the effects of 1/f noise. These devices currently have a LOD of 4 electronic charges in ambient conditions..