Question 1

What is an ELISA and how does it detect target proteins?

Accepted Answer

An ELISA, or enzyme-linked immunosorbent assay, detects specific target proteins in experimental samples through antibody binding. Antibodies conjugated to enzymes recognize target proteins coating the bottom of a 96-well plate. When substrate is added, an enzymatic reaction occurs, causing a color change that allows identification and quantification of the target protein.

Question 2

Why is a blocking buffer essential in ELISA procedures?

Accepted Answer

A blocking buffer covers nonspecific binding sites in experimental samples that could otherwise bind detector antibodies. Without blocking, enzymatic reactions may occur in wells lacking target protein, producing false positive results. This step prevents background signal and ensures accurate detection of only the target protein of interest.

Question 3

How do primary and secondary antibodies work together in an ELISA?

Accepted Answer

The primary antibody directly binds to the target protein with high affinity for a specific epitope region. The secondary antibody, typically raised in a different organism, recognizes and binds to the primary antibody. The secondary antibody is enzyme-conjugated, enabling the colorimetric reaction when substrate is added.

Question 4

What role does the microplate reader play in ELISA analysis?

Accepted Answer

The microplate reader quantifies protein concentration by measuring absorbance, or the amount of colored product, in each well. The absorbance is proportional to the target protein present. By comparing sample well absorbance to a standard curve of known protein concentrations, the reader determines the protein concentration in experimental samples.

Question 5

What is a sandwich ELISA and how does it differ from a standard ELISA?

Accepted Answer

In a sandwich ELISA, the 96-well plate is coated first with a primary antibody that recognizes the target protein, rather than coating with the target protein itself. The target protein binds between the plate-bound primary antibody and an enzyme-linked secondary antibody, creating a sandwich structure. This format is commonly used in pregnancy tests and cell line screening applications.

Question 6

How does a competitive ELISA detect antibodies in patient samples?

Accepted Answer

In a competitive ELISA, antibodies of interest in the sample bind to target protein attached to the plate bottom. When enzyme-linked detection antibodies are added, they find few binding sites because the sample antibodies have already bound the target protein. Colored wells indicate samples without the antibody of interest, making this format useful for detecting pathogen antibodies like HIV.

Question 7

What determines the detection limits of an ELISA assay?

Accepted Answer

Each ELISA kit has specific detection limits based on protein concentration ranges. Very low protein concentrations are too close to background levels of nonspecific staining and cannot be accurately detected. Very high concentrations may indicate excess protein or antibody was not properly washed away, affecting result accuracy.

The ELISA Method - Assessment Quiz