So once we form this secondary radioactively labeled antibody, we then mix this mixture of antibody with our polymer sheet that contains that antigen that is bound to the primary antibody. And what happens is, because this was formed to bind onto this blue primary antibody, this complex is formed. So the polymer sheet containing the antibody antigen complex is now exposed to a solution containing the radioactively labeled antibody. So we take the green mixture of antibodies. We reacted with the polymer sheet that contains the blue antibody bound onto the protein found on this second band. Now, the radioactive antibody will only bind to this band and not the other bands because only this second band contains this protein, the antibody bound onto the antigen because this was built specifically to bind onto this primary blue antibody.