Enzyme-linked immunosorbent assay (ELISA) using protein and antibody

1. What is the primary purpose of an ELISA test?
2. What is the name of the ELISA variant that involves using two antibodies to detect an antigen?
3. In which type of ELISA test is a labeled antigen used instead of a labeled antibody?
4. Which of the following is not a type of ELISA?
5. Which of the following is a common substrate used in ELISA tests?