Improved potassium-selective membrane using valinomycin as ionophore for ion-selective microdevices

Ion-selective field effect transistors (ISFETs) were tested for their suitability for clinical work. They were intended for use in the analysis of blood and serum, where the concentration of specific ions, e.g. sodium and potassium, is of critical importance. The optical sensitivity of ISFETs and a new membrane composition for use in the clinical chemistry were evaluated. ISFETs with a polyimide/valinomycin membrane were shown to operate satisfactorily in the presence of proteins, encouraging the further development of these ISFETs as clinical sensors. ETH 2041 (tetra-n-undecyl 3,3′, 4,4′–benzophenone tetracarboxylate) and DGD (diethylene dibenzoate) were the plasticizers used and their performances were compared. Valinomycin was used as ionophore. The membranes were calibrated using the dip (solutions in the 10−1–10−5 mol dm−3 KCl range) and the constant volume dilution methods. Both membrane compositions gave good Nernstian responses. The ETH 2041 plasticizer was found to yield devices more selective to potassium ion than the more easily usable DGD.