Western Blot needs both primary and secondary antibodies to successfully detect the antigen of interest. Western Blot involves probing the blocked membrane with a primary antibody that binds to a specific antigen or epitope on a group of antigens. In most cases, the primary antibody that binds to the antigen of interest in a western blot assay cannot be detected directly. Using tagged secondary antibodies that bind to the primary antibody helps to detect the target antigen via indirect detection.