Which statement about the role of biotin in the ABC method?

Which statement about the role of biotin in the ABC method?

• A. Biotin directly labels the primary antibody
• B. Biotin is not used in the method
• C. Biotin binds to the enzyme
• D. Biotin is conjugated to secondary antibodies to allow binding to streptavidin and form the detection complex

Answer: (D)

The main idea is that biotin acts as a tag on the secondary antibody to recruit an avidin/streptavidin–enzyme complex for detection. In ABC, after the primary antibody binds the antigen, a biotinylated secondary antibody attaches to that primary. Then streptavidin (or avidin) conjugated to an enzyme binds to the biotin on the secondary antibody, forming the detection complex at the antigen site. This strong biotin–streptavidin interaction enables a robust, amplified signal when the enzyme acts on its substrate. This explains why the statement is correct: biotin is attached to the secondary antibody to enable binding to streptavidin and creation of the detectable complex. The other options don’t fit because the biotin tag isn’t used to label the primary antibody directly, biotin is indeed used in the method, and the role is not that biotin binds directly to the enzyme but to streptavidin that carries the enzyme.

The main idea is that biotin acts as a tag on the secondary antibody to recruit an avidin/streptavidin–enzyme complex for detection. In ABC, after the primary antibody binds the antigen, a biotinylated secondary antibody attaches to that primary. Then streptavidin (or avidin) conjugated to an enzyme binds to the biotin on the secondary antibody, forming the detection complex at the antigen site. This strong biotin–streptavidin interaction enables a robust, amplified signal when the enzyme acts on its substrate.

This explains why the statement is correct: biotin is attached to the secondary antibody to enable binding to streptavidin and creation of the detectable complex. The other options don’t fit because the biotin tag isn’t used to label the primary antibody directly, biotin is indeed used in the method, and the role is not that biotin binds directly to the enzyme but to streptavidin that carries the enzyme.