A sensor for electrosensing an antigen in a test sample is disclosed. The sensor has two electrodes electrically disconnected and physically separated from each other, a layer of antibody immobilized on the surface of at least one of said electrodes. The antibody has specific binding reactivity with the antigen. Conductivity promotion molecules are conjugated with the antibody to improve electrical conductivity characteristics across the two electrodes. The antibody captures the antigen present in the test sample mixed in a buffer solution that comes into contact with the antibody-populated electrodes. This alters the electrical conductivity characteristic across the two electrodes in which an amount representative of the altering provides an indication for electrosensing of the antigen.