Hexacyanoferrate ion, [Fe(CN)(6)](4-), was immobilized by an ion-exchange reaction on the propylpyridiniumsilsesquioxane chloride polymer thin-film-coated SiO2/Al2O3 surface. The amount of [Fe(CN)(6)](4-) immobilized was 0.22 mmol g(-1) with a surface coverage of 9.6 x 10(-6) mmol cm(-2). A carbon paste electrode made with this material was prepared and its electrochemical properties studied. The electrode presented two well-defined redox peaks with midpoint potentials, E-m of 0.152 V vs SCE. This potential was not significantly affected by pH changes between 2 and 9.5. The electrode showed much reproducible responses and was successfully used to study the electrochemical oxidation of cysteine. (C) 2003 Elsevier Ltd. All rights reserved.