The development of an immunosensor system for the specific measurement of biomarkers will be discussed. Particular focus has been given to specifically immobilise biomolecules for optimum sensing. Formations of immunochemical reactions were reported using impedance spectroscopy with circuit fitting analysis to simulate physical properties at electrode interfaces. Gold and tantalum silicide interdigitated electrodes were used as transducers with an aminosilane polymer layer of controlled thickness as a host matrix for the immobilisation of monoclonal antibodies. Rabbit IgG-anti-rabbit IgG immunochemical reaction was used as a model system with later incorporation of disease marker assays such as S-IOO pp protein, prostate specific antigen and CA125 ovarian cancer. Impedance spectra were recorded in a frequency window from I MHz to 1 Hz. Labeless detection of the imrnunochemical event was carried out in a low conductivity medium by measuring changes in the resistance/capacitance of the polymer layer upon irnmobililisation ofthe antibody and subsequent antigen reaction. A labelled detection scheme based on the use of anti-rabbit IgG-HRP conjugates and amionethyl carbazole enzyme substrate were also performed. The catalytic oxidation of this species generated an insoluble product that deposited on the sensor surface and induced an impedance increase of the system. Results obtained by the different protocols were compared.