Direct visual detection of protein antigen: importance of surface concentration.

A new type of commercially available substrate was used for visualization of antigen binding to antibodies immobilized on the substrate surface. Addition of antigen induced sufficient increase of the protein layer to allow direct visualization, provided that the antibodies immobilized at the surface were immunosorbent isolated. This finding shows the importance of the surface concentration for direct optical visualization of antigen. The results are discussed in relation to previous reports that it is not possible to visualize directly the binding of protein antigen to surface-immobilized antibodies.