Which of the following best defines an ELISA and the functional role of an enzyme linked to an antibody in the assay?

• A. A molecular amplification method where antibodies are used to amplify DNA signals and the enzyme produces color by converting a nucleic acid substrate directly proportional to the amount of DNA present in the sample.
• B. A technique that relies on fluorescently labeled antigens to detect cellular fluorescence across different wells, requiring lasers and detectors calibrated to each antigen's emission spectrum and including extensive spectral unmixing procedures to quantify bound analyte precisely, because colorimetric enzymes are not used in this format.
• C. A culture-based diagnostic where bacteria are grown in the presence of enzyme-labeled antibodies and colony color indicates viability rather than the presence of antigen.
• D. An immunoassay that uses antibodies conjugated to enzymes; when the conjugated antibody binds its target and the enzyme's substrate is added, the enzyme converts substrate to a colored product, indicating specific binding.

Answer: (D)