A miniaturized ammonium sensor based on the integration of both ammonium and reference FETs in a single chip

A miniaturized sensor for ammonium detection based on the integration of both ammonium and reference FETs in a single chip, was fabricated by including nonactin in a plasticized PVC membrane deposited on the surface of the NH4+ ion-sensitive field effect transistor (ISFET) and by depositing a plasticized PVC membrane on the reference (non-sensitive) FET. A differential measurement mode between both FETs was used, this mode of measurement allowed to reduce interferences of Na+ and K+ ions, the effect of ionic strength and of temperature. The sensitivity of the ammonium detection was around 30 mV/pNH4+ and the detection limit 2 × 10−6M.