Thin platinum gate field effect transistors as ammonia sensors in liquid

We have earlier demonstrated that thin discontinuous hydrophobic platinum films, used as the gate metal of rnetal-oxide-semiconductor capacitors act as gas permeable structures. In this contribution we describe both a field effect capacitor and a field effect transistor which can detect molecular ammonia in aqueous solution without the need of a gas permeable membrane in front of the devices. More particularly we demonstrate that an increase of the operation temperature speeds up the recovery of the sensor signal after an ammonia sample pulse and how the devices can be used to measure the concentration of ammonium ions in a flow through system.