Biosensors based on surface concentration measuring devices — The concept of surface concentration

Abstract

Surface concentration measuring devices allow direct measurement of biomolecular interactions. These devices measure the surface concentration of, for example, interacting antigens or antibodies at solid surfaces.

We here exemplify the importance of using highly purified molecules together with an optimized immobilization technique for surface concentration measuring immunosensors. The immobilization of antibodies for the detection of human plasma fibronectin was compared to the reverse where the antigen was immobilized. The result was evaluated by in situ ellipsometry, an optical surface concentration measuring technique whereby the changes in polarization of light on reflection at a surface is measured.

It was found that immobilized fibronectin to a much greater extent interacted with antibodies in solution as compared to the reverse situation where the antibodies were immobilized. This was explained by the multivalency of antibody binding sites on each fibronectin molecule as compared to the two antigen binding sites on each antibody. The surface concentration of fibronectin interacting with immobilized antibodies was found to depend not only on the degree of purification of the antibodies but also on the immobilization technique.