Sulfonated thiophenes, sodium 2-(3-thienyloxy)ethanesulfonate (C6H7S2O4Na) and sodium 6-(3-thienyloxy)hexanesulfonate (C10H15S2O4Na), were synthesized and used in the fabrication of ion-selective electrodes (ISEs) sensitive and selective to Ag+. The Ag+-ISEs were prepared by galvanostatic electropolymerization of 3,4-ethylenedioxythiophene (EDOT) on glassy carbon (GC) electrodes, with either C6H7S2O4- or C10H15S2O4- as the charge compensator (doping ion) for p-doped poly(3,4-ethylenedioxythiophene) (PEDOT). Potentiometric measurements were carried out with these sensors, GC/PEDOT(C6H7S2O4-) and GC/PEDOT(C10H15S2O4-), to study and compare their sensitivity and selectivity to silver ions. PEDOT(C6H7S2O4-) and PEDOT(C10H15S2O4-) films were also studied by using other techniques such as cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), electrochemical quartz crystal microbalance (EQCM) and Fourier transform infrared spectroscopy (FTIR). Results froth the potentiometric measurements showed that the difference in length of the alkyl chain of the doping ions C6H7S2O4-and C10H15S2O4- has no significant effect on the sensitivity or selectivity of GC/PEDOT(C6H7S2O4-) and GC/PEDOT(C10H15S2O4-) sensors to Ag'. More differences can be seen in the cyclic voltammograms and EIS spectra of the sensors. FUR spectra confirmed that both C10H15S2O4- and C10H15S2O4- act as doping ions in the electrosynthesis of PEDOT based films and they are not irreversibly immobilized in the polymer backbone. (c) 2007 Elsevier Ltd. All rights reserved.