Photocurable pH-sensitive membrane for ion-selective field effect transistors

H+-ion sensitive ISFETs with photocured polyurethane-based polymer membranes with three different neutral carrier ionophores and four different plasticizers have been studied in 0.05 M TRIS–HCl solutions and in background solutions containing 140 mM of Na+ ions. The optimised membrane composition showing the best selectivity contains 2.2–2.5 wt.% of the ionophore (tridodecylamine), 36–41 wt.% of a plasticizer, and only 10 mol% of a lipophilic salt KTClPhB. The optimal ionophore/lipophilic salt ratio obtained in this work differs significantly from theoretically recommended for pH-sensitive ion-selective membranes. It is assumed that this is due to the participation of the ionophore (tertiary amine) and lipophilic additives (tetrachlorophenylborate anion) in additional photochemical reactions occurring during irradiation of the membrane matrix. Sensors with the optimised membrane composition showed sufficient sensor selectivity in front of sodium ions for clinical and biomedical applications and the lifetime of more than 3 months.