Which statement best describes Direct ELISA?

Which statement best describes Direct ELISA?

• A. It relies on secondary antibodies for signal amplification.
• B. It uses multiple different antibodies to detect different antigens.
• C. It detects activity by color change in a substrate directly bound to the antigen.
• D. Direct ELISAs use a conjugated primary antibody. Intended for the detection and quantification of a specific analyte.

Answer: (D)

Direct ELISA uses a primary antibody that is directly labeled with an enzyme, so the antibody itself reports the presence of the antigen. The antigen is captured on a plate, and the labeled antibody binds it; adding the substrate then yields a color change proportional to how much antigen is present. This setup lets you detect and quantify a specific analyte in a single step without any secondary antibody. That’s why the statement about using a conjugated primary antibody best describes Direct ELISA. The other ideas describe features of indirect or alternative ELISA formats (like signal amplification with secondary antibodies), or misunderstand how the color signal is generated.

Direct ELISA uses a primary antibody that is directly labeled with an enzyme, so the antibody itself reports the presence of the antigen. The antigen is captured on a plate, and the labeled antibody binds it; adding the substrate then yields a color change proportional to how much antigen is present. This setup lets you detect and quantify a specific analyte in a single step without any secondary antibody. That’s why the statement about using a conjugated primary antibody best describes Direct ELISA. The other ideas describe features of indirect or alternative ELISA formats (like signal amplification with secondary antibodies), or misunderstand how the color signal is generated.