Which statement about ELISA formats is true?

Which statement about ELISA formats is true?

• A. Direct ELISA uses a conjugated secondary antibody.
• B. Sandwich ELISA requires two antibodies to capture the antigen, pinching it between them.
• C. Indirect ELISA detects the protein activity rather than presence.
• D. ELISA is not used to quantify proteins.

Answer: (B)

In ELISA formats, the way you detect and quantify the target depends on how many antibodies are used and how the signal is generated. The statement that is true describes a sandwich ELISA, which uses two antibodies to recognize the antigen. One antibody captures the antigen on the plate, and a second antibody binds a different epitope on the same antigen, forming a “sandwich.” The detection antibody is typically linked to an enzyme that produces a measurable signal when substrate is added, and this signal is proportional to the amount of antigen present. This two-antibody approach increases specificity and sensitivity, especially for larger proteins with multiple epitopes. The other descriptions don’t fit the common ELISA formats: a direct ELISA usually employs a single labeled antibody without a secondary antibody; an indirect ELISA detects antibodies in a sample using a secondary antibody for detection, not the antigen itself; and ELISA is indeed used to quantify protein amounts, not just to indicate presence.

In ELISA formats, the way you detect and quantify the target depends on how many antibodies are used and how the signal is generated. The statement that is true describes a sandwich ELISA, which uses two antibodies to recognize the antigen. One antibody captures the antigen on the plate, and a second antibody binds a different epitope on the same antigen, forming a “sandwich.” The detection antibody is typically linked to an enzyme that produces a measurable signal when substrate is added, and this signal is proportional to the amount of antigen present. This two-antibody approach increases specificity and sensitivity, especially for larger proteins with multiple epitopes. The other descriptions don’t fit the common ELISA formats: a direct ELISA usually employs a single labeled antibody without a secondary antibody; an indirect ELISA detects antibodies in a sample using a secondary antibody for detection, not the antigen itself; and ELISA is indeed used to quantify protein amounts, not just to indicate presence.