The blot is blocked to prevent nonspecific adsorption of the immunological reagents.  Antibodies are then bound to the proteins immobilized on the membrane, and the antigen is detected by labeling the antibodies with conveniently identified tags.  Common labeling methods for chemiluminescent detection include anti-immunoglobulin antibody-coupled enzymes such as horseradish peroxidase, which catalyzes the oxidation of luminol and in turn releases light.

Protocol: Immunoblotting: Antigen Detection Using Chemiluminescence Protocol