We report an important observation that the surface conductivity of antibody layer immobilized on polylysine-coated glass substrate decreases upon the formation of complex with their specific antigens. This change in conductivity has been ob- served for both monoclonal and polyclonal antibodies. The conductance of monoclonal mouse IgG immobilized on polylysine-coated glass substrate changed from 1.02×10?8 ??1 to 1.41×10?11 ??1 at 10 V when complex is formed due to the specific biomolecular interactions with rabbit anti-mouse IgG F(ab′)2. Similar behavior was observed when the same set up was tested in two clinical assays: (1) anti-Leishmania antigen polyclonal antibodies taken from Kala Azar positive patient serum interacting with Leishmania promastigote antigen, and (2) anti-p21 polyclonal antibodies interacting with p21 antigen. The pro- posed concept can represent a new immunodiagnostic technique and may have wide ranging applications in biosensors and nanobiotechnology too. We report an important observation that the surface conductivity of antibody layer immobilized on polylysine-coated glass substrates decreases upon the formation of complex with their specific antigens. This change in conductivity has been ob- served for both monoclonal and polyclonal antibodies. The conductance of monoclonal mouse IgG immobilized on polylysine-coated glass substrate changed from 1.02 × 10 ~ 8 ~ 1 to 1.41 × 10 ~ 11 ~ 1 at 10 V when complex is formed due to the specific biomolecular interactions with rabbit anti-mouse IgG F (ab (1) anti-Leishmania antigen polyclonal antibodies taken from Kala Azar positive patients serum interacting with Leishmania promastigote antigen, and (2) anti-p21 polyclonal The pro-posed concept can represent a new immunodiagnostic technique and may have wide ranging applications in biosensors and nanobiotechnology too.