A new concept in ion sensing mimicking allosteric membranes in biological systems was proposed and demonstrated using fluoride-effector Na+ selective electrodes (Na-ISEs). DOS-plasticized PVC membranes containing p-tert-butylcalix[4]arene tetraethyl ester (NaX) and 4-[(4-tert-butyl-2methylphenoxy)methyllphenyl boronic acid (50 mol% compared to NaX) were found to give the best characteristic of Na-ISEs upon conditioning the membranes in 10(-2) M NaF: a response slope of 57.48 mV per decade and detection limit of 7.42 x 10(-7) M. The selectivity coefficients (log K-Na,j(pot)) for the optimal electrode were -2.29, -2.84, -3.16, -3.42, and -3.01 for K+, Li+, Cs+, Mg2+ and Ca2+, respectively. The optimal electrodes also gave good reversibility and could be used in a wide range of pH (pH 3.6-9.7). The fabricated Na-ISEs were found to have membrane resistances (R-m) varied with concentrations of fluoride ions used in membrane conditioning steps. Electrochemical impedance spectra showed a linear relationship between R-m, and the logarithm of the concentration range of fluoride ions from 1 x 10(-1) to 1 x 10(-8) M. Conditioning optimal membranes with various concentrations of Bu4NF gave a non-linear relationship. The proposed membrane electrode, thus, showed permselectivity toward Na+ using F- as an effector. Therefore, the proposed new concept led to the fabrication of a bifunctional sensor: a potentiometric sensor for sodium ion and an impedimetric sensor for fluoride ion. (C) 2013 Elsevier Ltd. All rights reserved.