An enzyme-linked immunosorbent assay (ELISA) is typically performed to detect the presence and/or amount of a target protein of interest within an experimental sample. Detection of the target protein is made possible by antibodies, which make the ELISA an immunoassay. Through a series of incubation and washing steps, these antibodies, which are frequently linked, or conjugated, to an enzyme, will detect protein coating the bottom of a well on a microtiter plate. When exposed to a substrate, antibody-bound enzyme will cause a color change, thereby indicating the presence of the protein of interest in the sample.

In this video, the theory behind how ELISAs work is explained, including a discussion of both primary and secondary antibody binding and the importance of blocking steps. Theory is followed by practice, as the video progresses to an explanation of the step-by-step procedure. Finally, variations of the standard ELISA such as the sandwich and competitive ELISAs are introduced, and real-world applications of this method, such as in over-the-counter pregnancy tests are explained.

1. For which of the following applications could an ELISA be used?

- To neutralize trypsin within a sample.

- To determine the size of a plasmid within a sample.

- To determine the presence or absence of contamination within a sample.

- To determine the presence or absence of a specific protein within a sample.

2. The target protein is recognized by...

- ...the substrate.

- ...buffer enzymes.

-...unlabeled viral particles.

-...the primary antibody.

3. The absorbance measured for each well is _____to the amount of target protein present in each sample. (cell culture media harvested from human anti-body-producing cell lines).

- equal

- not directly related

- inversely proportional

- directly proportional