Figure 4.

Schematic illustration for the label-free voltammetric immunosensors. The primary antibody is coated on the electrode surface and the electro-active residues in the antibody structure give a specific current response. Upon the binding of the target antigen with the antibody, the specific current response of the antibody layer changes. This change can either be an increase or a decrease depending on the structure of the antigen and/or the conformational changes that would occur upon the formation of the antigen-antibody complex. Then, the current responses would be further altered with the binding of the secondary antibody, which would also contribute to the current response with its intrinsic electro-activity.