  We employ noise spectroscopy and transconductance measurements to establish
the optimal regimes of operation for our fabricated silicon nanowire
field-effect transistors (Si NW FETs) sensors. A strong coupling between the
liquid gate and back gate (the substrate) has been revealed and used for
optimisation of signal-to-noise ratio in sub-threshold as well as
above-threshold regimes. Increasing the sensitivity of Si NW FET sensors above
the detection limit has been predicted and proven by direct experimental
measurements.
