Reference field effect transistors based on chemically modified ISFETs

Different hydrophobic polymers were used for chemical modification of ion-sensitive field effect transistors (ISFETs) in order to prepare a reference FET (REFET). Chemical attachment of the polymer to the ISFET gate results in a long lifetime of the device. Properties of polyacrylate (polyACE) REFETs are described in detail. The polyACE-REFET is superior to other polymer modified REFETs, showing an excellent pH insensitivity (?1 mV pH^?1), a long lifetime and an electrically identical behaviour as an unmodified pH ISFET or a cation-selective PVC-MEMFET (membrane FET). The cation permeselectivity of the polymer can be significantly reduced by addition of immobile cations. The applicability of a polyACE-REFET in differential measurements with a pH ISFET and a K⁺ MEMFET is demonstrated.