Final answer:
Indirect ELISA detects specific antibodies against an antigen using a labeled secondary antibody, while Sandwich ELISA quantifies an antigen using two antibodies and is highly sensitive.
Step-by-step explanation:
The main difference between Indirect ELISA and Sandwich ELISA lies in their methodology and purpose. In an Indirect ELISA, a known antigen is attached to the plate to detect specific antibodies in a sample, and it uses a labeled secondary antibody for detection. Conversely, the Sandwich ELISA involves capturing the antigen with a primary antibody, then detecting it with a labeled secondary antibody; it is a highly specific test that can quantify antigen levels.
Both Indirect ELISA and Sandwich ELISA use labeled antibodies, but in distinct ways. The statement 'Sandwich ELISA is also known as direct ELISA' is incorrect because Sandwich ELISA uses two antibodies (a capture and a detection antibody), whereas direct ELISA uses only one labeled primary antibody. The goal of the Sandwich ELISA is to specifically quantify the antigen in a sample with high sensitivity, while the goal of an Indirect ELISA is primarily to detect the presence of antibodies against an antigen.