Miniaturized sodium-selective sensors based on silicon back-side contact structure with novel self-plasticizing ion-selective membranes

The design of durable miniaturized back-side contact (BSC) sensors with polymeric Na+-selective membranes based on self-plasticizing matrices consisted of isodecylacrylate (IDA) and acrylonitrile (ACN) is presented. Two types of polymers, linear copolymer obtained by emulsion method (IDA/ACN) and cross-linked with hexanediol diacrylate (HDDA) terpolymer (IDA/ACN/HDDA) prepared by photopolymerization were examined for this purpose. It was found that membranes of IDA/ACN/HDDA matrix exhibited excellent adhesion to silicon nitride surface of the chip. Sensors with such membranes containing 2 wt.% of 4-tert-butylcalix[4]arene-tetraacetic acid tetraethyl ester along with 40 mol% of potassium tetrakis(4-chlorophenyl)borate (KTpClPB) exhibited fast (t((95)) < 10 s) and Nernstian response (59.4 +/- 0.4 mV per decade) over 1.3 x 10(-5)-2.3 x 10(-1) M sodium concentration range and the selectivity comparable to observed for classical ISEs with PVC-based membranes with the same ionophore. It was confirmed that the intermediate pHEMA/NaCl layer introduced between polymeric membrane and Ag/AgCl sensing site of the chip improves the EMF stability and reproducibility of sensors. Sensors have maintained their working characteristics for at least 8 months. (C) 2003 Elsevier B.V. All rights reserved.