Question 1

Which of the following best describes the principle behind an ELISA assay?

Accepted Answer

It relies on enzyme-linked antibodies binding to antigens, producing a color change.

Question 2

In an indirect ELISA, what is the role of the secondary antibody?

Accepted Answer

It binds to the primary antibody and is conjugated to an enzyme.

Question 3

A researcher wants to measure the concentration of cortisol in blood samples using ELISA. Which step ensures that only the specific antigen is detected and not other proteins?

Accepted Answer

Using a blocking buffer to prevent nonspecific binding.

Question 4

Which equation would you use to calculate the concentration of antigen in a sample based on ELISA absorbance readings?

Accepted Answer

$$C = \frac{A}{\epsilon \cdot l}$$

Question 5

Why is it important to perform ELISA assays in triplicate?

Accepted Answer

To increase the accuracy and reliability of the results by reducing random error.

Question 6

A blue color develops in an ELISA well after adding tetramethylbenzidine (TMB). What does this indicate?

Accepted Answer

The enzyme-linked antibody has bound to the antigen, indicating its presence.

Question 7

Which of the following is a real-world application of ELISA?

Accepted Answer

Detecting genetically modified proteins in crops.

Question 8

In the context of ELISA, what is an epitope?

Accepted Answer

The specific region of an antigen recognized by an antibody.

Question 9

A competitive ELISA is used to detect a drug metabolite in urine. Which statement best describes how the result is interpreted?

Accepted Answer

The more metabolite present, the weaker the color change.

Question 10

During an indirect ELISA, what would happen if you failed to wash out unbound primary antibodies before adding the secondary antibody?

Accepted Answer

The assay would show increased background signal, reducing specificity.

Question 11

Which of the following is NOT a typical use for ELISA assays?

Accepted Answer

Sequencing the genome of bacteria.

Question 12

Why are polystyrene plates used in ELISA assays?

Accepted Answer

They allow hydrophobic interactions to adsorb proteins (antigens) to the wells.

Question 13

A patient’s blood sample is tested for HCG using a sandwich ELISA. Which combination of antibodies is required?

Accepted Answer

Capture antibody bound to the plate and detection antibody conjugated to an enzyme.

Question 14

Which formula would you use to determine the dilution factor if you dilute a sample 1:10 and then 1:5?

Accepted Answer

$$DF = 1:10 	imes 1:5 = 1:50$$

Question 15

Which step in an indirect ELISA ensures that only the antigen-specific signal is measured?

Accepted Answer

Washing out unbound antibodies after each antibody addition.

Question 16

If you cross-contaminate samples during an ELISA, what is the most likely outcome?

Accepted Answer

The results will be unreliable due to false positives or negatives.

Question 17

Which of the following best explains why controls are critical in ELISA experiments?

Accepted Answer

They help distinguish true positive and negative results from background noise.

Question 18

A food manufacturer uses ELISA to test for peanut allergens in their products. Which antibody would be most appropriate for this assay?

Accepted Answer

An antibody specific to the peanut allergen epitope.

Question 19

In ELISA, what is the function of the enzyme conjugated to the antibody?

Accepted Answer

It catalyzes a reaction with the substrate to produce a measurable color change.

Question 20

Which of the following scenarios would most likely result in a false negative ELISA result?

Accepted Answer

The primary antibody does not recognize the antigen present in the sample.

ELISA: Principles, Applications, and Laboratory Practice

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