A miniaturized pH sensor based on the voltammetric determination of the potential difference between a pH dependent toluidine blue O modified redox polymer and a pH independent osmium complex modified redox polymer was developed. Gold micro electrodes of various dimensions were modified with the two redox polymers by non-manual deposition procedures. Square wave voltammetry was used to determine the oxidation potentials of the polymer bound redox species allowing the precise determination of the pH value of the electrolyte solution without the need of a stable reference electrode. (C) 2014 Elsevier Ltd. All rights reserved.