Long-lived potentiometric sensors with poly(vinylchloride) and photopolymerized polyacrylate matrix anion sensitive membranes, applied on field effect transistors and silver coated ceramic substrates

Long-lived potentiometric sensors with conventional plasticized poly(vinylchoride) and photopolymerized polyacrylate matrixes membranes, sensitive to the nitrate-, fluoborate-, dicyanoaurate- and dicyanoargentate (DCA)-ion, were studied. Three kinds of transducers: the encapsulated pH-sensitive field-effect transistors (FET) with Ta2O5 and SiO2/Si3N4 gate insulators and a silver coated ceramic substrate (AgCer) were used for sensors preparation. The application of an intermediate hydrophobic acrylate type polymer layer (HAPL) between the ion sensitive PVC matrix membrane and the transducer surface leads to a dramatic rise in the ISFET life time of up to 4 months and, on the contrary, to reduced durability of the AgCer based sensors. The effects of the membrane plasticizer and thickness on the performance, selectivity, dynamic characteristics and durability of these sensors were studied. The characteristics of the different transducers, covered with photopolymerized DCA-sensitive membranes, were compared. All these sensors did not contain intermediate HAPL. The best transducer for sensors, manufactured by the photopolymerization technique, was found to be an n-channel depletion mode FET, SiO2/Si3N4 gate insulator. These sensors differed from others by their high durability and good reproducibility of signal and linear performance slope during continuous measurements in batch and FIA modes. (C) 1998 Elsevier Science S.A. All rights reserved.