Demonstration of a new biosensing concept for immunodiagnostic applications based on change in surface conductance of antibodies after biomolecular interactions.

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 observed for both monoclonal and polyclonal antibodies. The conductance of monoclonal mouse IgG immobilized on polylysine-coated glass substrate changed from 1.02x10(-8) ohm(-1) to 1.41x10(-11) ohm(-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 proposed concept can represent a new immunodiagnostic technique and may have wide ranging applications in biosensors and nanobiotechnology too.

1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide interference with Lowry method.

1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) was tested for interference with the Lowry method of protein determination. The EDC interference was nearly additive at both 660 and 750 nm. Blue-colored complex developed in the case of EDC and showed maximum absorbance at 750 nm, similar to the bovine serum albumin (BSA) estimation. In time response analysis, blue-colored complex was developed after 30 min of incubation in both cases (EDC and BSA); therefore, it followed the same kinetic pattern of color development as that of BSA. Interference is believed to be caused by the reduction of the folin-ciocalteu reagent by EDC, resulting in increased blue-colored complex and apparently causing increased protein content of the sample.