Anti-HER-3 antibody was used for the first time in a disposable immunosensor based on indium tin oxide (ITO) substrate for HER-3 quantification. Anti-HER-3 was immobilized onto ITO substrate by 3-aminopropyl)triethoxysilane (APTES) and glutaraldehyde. This highly sensitive immunosensor was capable of detecting concentrations of HER-3 down to the femtogram/ml level by investigating changes in the charge transfer resistance (R-ct) using electrochemical impedance spectroscopy (EIS). Construction of ITO layers was carefully investigated using a broad range of techniques such as voltammetry, EIS, atomic force microscopy (AFM), and scanning electron microscopy (SEM). Meanwhile, in an immunosensor system, the "single frequency impedance" technique was first used for characterization of interaction between HER-3 and anti-HER-3. Eventually, the proposed ITO-based immunosensor was applied to artificial serum samples spiked with HER-3. (C) 2013 Elsevier Inc. All rights reserved.