ELISA - 50 Most Important MCQs for ASRB NET

1. Which of the following is the principle of ELISA?

A) Antigen-antibody interaction

Answer: A

Explanation: ELISA is based on the specific interaction between an antigen and its antibody.

2. What enzyme is commonly used in ELISA?

B) Horseradish peroxidase (HRP)

Answer: B

Explanation: HRP is widely used because it gives a color change when substrate is added.

3. The substrate used in ELISA for HRP is typically:

B) TMB (3,3-,5,5--Tetramethylbenzidine)

Answer: B

Explanation: TMB produces a blue color upon reaction with HRP.

4. The final detection in ELISA is usually done using:

C) Spectrophotometer

Answer: C

Explanation: Color change is measured as optical density at a specific wavelength.

5. Which of the following is NOT a type of ELISA?

C) Reverse

Answer: C

Explanation: Reverse ELISA is not a standard type.

6. Which ELISA type uses two antibodies to capture and detect the antigen?

B) Sandwich

Answer: B

Explanation: Sandwich ELISA uses a capture and detection antibody for high specificity.

7. In indirect ELISA, what is coated on the plate?

Answer: D

Explanation: Antigen is immobilized, and antibody detection follows.

8. In competitive ELISA, the color intensity is:

B) Inversely proportional to antigen concentration

Answer: B

Explanation: Higher antigen reduces antibody binding - less color.

9. Which is the most sensitive ELISA format?

D) Sandwich

Answer: D

Explanation: Sandwich ELISA has higher sensitivity due to dual-antibody use.

10. What is used as the solid phase in ELISA?

C) Microtiter plate (Polystyrene)

Answer: C

Explanation: Polystyrene plates are used due to their ability to adsorb proteins.

11. ELISA is commonly used to detect:

D) Antigens and antibodies

Answer: D

Explanation: ELISA can detect both types depending on the assay design.

12. Which disease is commonly diagnosed using ELISA?

B) HIV

Answer: B

Explanation: HIV diagnosis via antibody detection using ELISA.

13. ELISA is not suitable for detecting:

C) mRNA

Answer: C

Explanation: ELISA detects proteins, not nucleic acids like mRNA.

B) Sandwich ELISA

Answer: B

Explanation: Sandwich format is often used to detect hCG in urine.

15. What is used to block nonspecific binding in ELISA?

C) Blocking agents like BSA or skim milk

Answer: C

Explanation: Blocking agents prevent nonspecific protein binding to the plate.

16. Which of the following is essential to reduce false positives in ELISA?

B) Proper washing steps

Answer: B

Explanation: Washing removes unbound reactants and reduces background noise.

17. Why is the enzyme label used in ELISA?

C) To amplify the signal via color reaction

Answer: C

Explanation: The enzyme catalyzes a colorimetric reaction for detection.

18. TMB substrate turns which color in presence of HRP?

A) Blue

Answer: A

Explanation: TMB gives a blue color which turns yellow upon acid stop.

19. Washing buffer used in ELISA typically contains:

A) PBS + Tween-20

Answer: A

Explanation: Tween-20 helps remove non-specific interactions.

20. To stop the enzyme reaction in ELISA, one adds:

A) HCl or H2SO4

Answer: A
Explanation: Acid stops the enzymatic reaction and stabilizes color for reading.

21. Which step in ELISA enhances specificity?

Use of monoclonal antibodies

Answer: Use of monoclonal antibodies

Explanation: Monoclonal antibodies bind to a single epitope, increasing specificity.

22. What color is observed in ELISA with alkaline phosphatase and PNPP substrate?

Yellow

Answer: Yellow

Explanation: Alkaline phosphatase converts PNPP into a yellow product.

23. What is the role of the secondary antibody in indirect ELISA?

To bind to the primary antibody and carry enzyme label

Answer: To bind to the primary antibody and carry enzyme label

Explanation: Secondary antibody enhances detection signal.

24. In sandwich ELISA, the sample is added after:

Coating with capture antibody

Answer: Coating with capture antibody

Explanation: Antigen in the sample binds to the capture antibody.

25. What is the main limitation of direct ELISA?

Low sensitivity

Answer: Low sensitivity

Explanation: Lack of amplification due to single antibody results in lower sensitivity.

26. Which ELISA type is best for small antigens?

Competitive ELISA

Answer: Competitive ELISA

Explanation: Small antigens can't be sandwiched, so competition format is used.

27. In ELISA, 'signal amplification' is achieved by:

Using enzyme-labeled secondary antibodies

Explanation: Increases the detectable signal.

28. A blank in ELISA is used to:

Zero the spectrophotometer

Answer: Zero the spectrophotometer

Explanation: It corrects the baseline reading.

29. What does OD stand for in ELISA?

Optical Density

Answer: Optical Density

Explanation: OD indicates the absorbance or color intensity.

30. ELISA plates are incubated at:

37-C typically

Answer: 37-C typically

Explanation: This temperature facilitates antigen-antibody reactions.

31. Which reagent is used to develop color in ELISA?

Substrate like TMB

Answer: Substrate like TMB

Explanation: TMB reacts with HRP to produce a color change.

32. What is the advantage of ELISA over RIA?

No radioactive hazard

Answer: No radioactive hazard

Explanation: ELISA uses enzymes, making it safer and easier to handle.

33. ELISA is classified as a:

Quantitative assay

Answer: Quantitative assay

Explanation: It allows measurement of analyte concentration.

34. The microtiter plate used in ELISA has how many wells?
Typically 96

Answer: Typically 96

Explanation: Standard ELISA plates contain 96 wells.

35. Which factor does NOT affect ELISA results?

Color of microtiter plate

Answer: Color of microtiter plate

Explanation: ELISA uses clear plates, but color itself doesn't affect binding.

36. The term 'titre' in ELISA refers to:

Concentration of antibodies

Answer: Concentration of antibodies

Explanation: It represents the dilution level that still gives a positive result.

37. Which ELISA type is best when only one antibody is available?

Direct ELISA

Answer: Direct ELISA

Explanation: It needs only one enzyme-labeled antibody.

38. In sandwich ELISA, higher signal indicates:

Higher antigen concentration

Answer: Higher antigen concentration

Explanation: More antigen = more enzyme binding = more signal.

39. Why is incubation time important in ELISA?

Ensures complete binding

Answer: Ensures complete binding

Explanation: Proper time allows antigens/antibodies to bind efficiently.

40. What does a standard curve in ELISA represent?

Relation between OD and antigen concentration

Answer: Relation between OD and antigen concentration

Explanation: It's used to quantify unknown samples.

Coating with antigen/antibody

Answer: Coating with antigen/antibody

Explanation: Blocking prevents nonspecific adsorption to plate.

42. Washing steps are repeated between steps to:

Remove unbound materials

Answer: Remove unbound materials

Explanation: Ensures specific signal and reduces background.

43. ELISA was invented by:

Engvall and Perlmann

Answer: Engvall and Perlmann

Explanation: They introduced the method in 1971.

44. Color change in ELISA is proportional to:

Amount of antigen or antibody

Answer: Amount of antigen or antibody

Explanation: Depends on ELISA type but indicates quantity.

45. The enzyme used in ELISA should be:

Stable and active in reaction conditions

Answer: Stable and active in reaction conditions

Explanation: Stability is key to consistent performance.

46. What is the first step in a typical indirect ELISA?

Coating antigen

Answer: Coating antigen

Explanation: Antigen is immobilized on the plate surface.

47. ELISA plate readings are taken at:

450 nm (for TMB)

Answer: 450 nm (for TMB)

48. Why are replicates used in ELISA?

To increase accuracy

Answer: To increase accuracy

Explanation: Minimizes experimental error.

49. ELISA can be used for plant disease diagnosis by detecting:

Pathogen-specific proteins or antibodies

Answer: Pathogen-specific proteins or antibodies

Explanation: ELISA detects presence of plant pathogens.

50. Which of the following improves ELISA sensitivity?

High affinity antibodies

Answer: High affinity antibodies

Explanation: Better binding increases assay sensitivity.