Question 1

Which of the following best describes the principle behind the ELISA (Enzyme-Linked Immunosorbent Assay) technique?

Accepted Answer

It uses antibodies to detect and quantify proteins in a sample by generating a measurable signal through an enzyme-catalyzed reaction.

Question 2

In a sandwich ELISA, which component is immobilized on the microtiter well to capture the analyte from the sample?

Accepted Answer

The primary antibody specific to the analyte

Question 3

Which of the following steps is unique to the indirect ELISA compared to the sandwich ELISA?

Accepted Answer

Addition of a secondary antibody that recognizes the primary antibody

Question 4

A researcher is using an ELISA to detect the presence of a viral antigen in patient serum. Which of the following would increase the sensitivity of the assay?

Accepted Answer

Using a fluorescent substrate and reading the signal with a sensitive detector

Question 5

In a competitive ELISA, what is the relationship between the concentration of analyte in the sample and the signal detected?

Accepted Answer

The signal is inversely proportional to the analyte concentration

Question 6

Which equation best represents the relationship between absorbance ($A$) and concentration ($c$) in a quantitative ELISA, assuming Beer-Lambert Law applies?

Accepted Answer

$A = \epsilon \cdot l \cdot c$

Question 7

Why is it important to include a standard curve in quantitative ELISA experiments?

Accepted Answer

To accurately determine the concentration of analyte in unknown samples by comparing their signal to known standards

Question 8

Which of the following is a potential source of error in ELISA that could lead to false positive results?

Accepted Answer

Non-specific binding of the secondary antibody to the plate

Question 9

In the context of ELISA, what is the role of the enzyme conjugated to the secondary antibody?

Accepted Answer

It catalyzes a reaction that produces a detectable signal, such as color or fluorescence.

Question 10

A patient’s serum is tested for a specific antigen using a sandwich ELISA. The absorbance measured is lower than the lowest standard on the standard curve. What is the most appropriate next step?

Accepted Answer

Repeat the assay with a higher volume of sample or concentrate the sample.

Question 11

Which of the following best explains why washing steps are critical between additions in an ELISA protocol?

Accepted Answer

To remove unbound reagents and reduce background signal, increasing assay specificity

Question 12

In a direct ELISA, which of the following is true regarding the detection of the analyte?

Accepted Answer

The primary antibody is directly conjugated to the enzyme

Question 13

A scientist is designing an ELISA to detect a low-abundance protein in blood. Which modification would most likely improve the assay’s sensitivity?

Accepted Answer

Using a substrate that produces a fluorescent product and a sensitive detector

Question 14

Which of the following is the correct order of steps in a typical sandwich ELISA?

Accepted Answer

Coat plate with capture antibody, add sample, add detection antibody, add enzyme substrate

Question 15

If the enzyme used in an ELISA catalyzes multiple cycles of a reaction that generates a fluorescent product, which of the following best describes the effect on the assay?

Accepted Answer

It amplifies the signal, allowing detection of lower concentrations of analyte.

Question 16

Which of the following is a reason to use a secondary antibody conjugated to an enzyme in an indirect ELISA?

Accepted Answer

To amplify the signal and increase sensitivity of detection

Question 17

A clinical laboratory is using ELISA to screen for HIV antibodies in patient samples. Which type of ELISA is most appropriate for this application?

Accepted Answer

Indirect ELISA

Question 18

Which of the following is a key advantage of using ELISA over other immunoassays?

Accepted Answer

It allows for quantitative measurement of analyte concentration using a standard curve.

Question 19

In a sandwich ELISA, what is the function of the detection antibody?

Accepted Answer

It binds to a different epitope on the analyte, allowing for specific detection.

Question 20

A researcher observes high background signal in an ELISA experiment. Which of the following is the most likely cause?

Accepted Answer

Insufficient washing between steps leading to unbound enzyme remaining on the plate

ELISA (Enzyme-Linked Immunosorbent Assay): Principles and Applications

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