Immunoelectrodes in protein detection: comparison between glassy carbon and a semimetallic Ni/P thin film as binding support. Biological applications.

Though immunoelectrodes can allow direct detection of very low protein amounts (about 0.1 pmol) in vitro and in vivo, they are not yet widely used because they need quality improvement. Based on a few works devoted to the basic electrochemical phenomenon occurring when antibodies are linked onto a solid support and during antigen/antibody complex formation, we have coated two different supports with antibodies: the classical glassy carbon fiber or an epoxy plate covered with an amorphous semimetallic (nickel/phosphorus) thin film obtained by means of an electrochemical deposit. The antibody/antigen complex formation induces direct and/or indirect ionic movements and a current flow through the conductive support toward a very low-noise and high-sensitivity preamplifier stage in an I/V configuration. The proposed electrochemical treatment (hydrophilization), applied to both carbon and Ni/P electrodes, improves antibody binding and reliability of the response to antigens. The Ni/P probes present several advantages when compared to carbon fiber: better conductivity, possibility of surface quality control, and semimetallic nature, making them unbreakable. Several applications were proposed: somatostatin-14 detection with both carbon fiber and Ni/P plate electrodes, and histamine detection in simple and complex fluid media. Dose-response curves and analysis of the results lead us to conclude that the obtained currents are directly related to the quantity of antigen.