Unit 7: Immunological assays - Practice Quiz

1 What does the abbreviation ELISA stand for?

2 ELISA is primarily used to detect the interaction between which two molecules?

3 Which type of plate is most commonly used to perform an ELISA?

4 The enzyme in an ELISA reaction produces a detectable signal by acting on a specific:

5 Which enzyme is commonly conjugated to antibodies in ELISA?

6 In a typical ELISA, a positive result is usually indicated by:

7 Which instrument is used to measure the color intensity of the final ELISA product?

8 The step of adding a protein solution to block unoccupied sites on the plate is called:

9 Why is a washing step included between ELISA stages?

10 Which ELISA format uses two antibodies that bind to different sites of the same antigen?

11 In an indirect ELISA, the enzyme label is attached to the:

12 The molecule that is coated onto the plate surface in a direct ELISA is usually the:

13 The specificity of ELISA is mainly due to:

14 Which of the following is a common application of ELISA?

15 In competitive ELISA, the sample antigen competes with labeled antigen for binding to the:

16 What is the purpose of the stop solution in an ELISA?

17 The optical density (OD) measured in an ELISA is generally proportional to the:

18 Which of these is NOT a standard component of an ELISA test?

19 In ELISA, the term immunosorbent refers to the:

20 A major advantage of ELISA over many other immunoassays is that it:

21 In a sandwich ELISA, a researcher coats the plate with a capture antibody, adds the sample antigen, then adds a detection antibody conjugated to an enzyme. What is the primary requirement for the antigen being detected using this format?

22 A student observes a strong color signal in the negative control wells of an indirect ELISA. Which of the following is the most likely cause?

23 Which enzyme-substrate pair is commonly used in ELISA and produces a yellow color upon reaction?

24 In an indirect ELISA used to detect anti-HIV antibodies, what is directly immobilized on the microtiter plate surface?

25 A competitive ELISA shows an inverse relationship between analyte concentration and signal. This means that:

26 Why are wash steps critical between each stage of an ELISA protocol?

27 In an ELISA, the optical density (OD) of a test sample is and the cut-off value is . How should this result be interpreted?

28 Which component provides the specificity of antigen detection in a direct ELISA?

29 The addition of a stop solution (e.g., dilute ) to an HRP-TMB ELISA reaction serves to:

30 A sandwich ELISA is generally more sensitive than a direct ELISA primarily because:

31 In an indirect ELISA, the secondary antibody is described as anti-species. What does this mean?

32 During ELISA optimization, a technician finds that increasing the primary antibody beyond a certain concentration no longer increases signal. This plateau indicates:

33 Which of the following best explains why a standard curve is prepared in a quantitative ELISA?

34 A false-negative ELISA result for antibody detection could occur if:

35 Which property makes microtiter plates made of polystyrene suitable for ELISA?

36 If the enzyme conjugate in an ELISA is accidentally omitted, what result is expected?

37 In a competitive ELISA for a small hapten, why is the competitive format preferred over a sandwich format?

38 The wavelength at which OD is measured in an ELISA depends primarily on:

39 A technician runs an ELISA and gets weak signal in all wells including positive controls. Which cause is most consistent with this observation?

40 Which statement correctly distinguishes direct from indirect ELISA?

41 In a sandwich ELISA, a researcher observes strong signal in the negative control wells that contain only buffer and no antigen. The capture antibody, detection antibody, and enzyme-conjugate were all added normally. Which explanation most likely accounts for this false-positive background?

42 A competitive ELISA is used to quantify a small hapten. In this format, the relationship between analyte concentration and measured absorbance is:

43 The 'hook effect' (prozone) in a sandwich ELISA produces which counterintuitive result at very high antigen concentrations?

44 A standard curve for a direct ELISA gives absorbance values that plateau at high antigen concentrations. Which statement about interpreting an unknown sample reading in this plateau region is correct?

45 Why is TMB (3,3',5,5'-tetramethylbenzidine) commonly stopped with sulfuric acid () before reading at 450 nm rather than reading the blue product at 650 nm?

46 A four-parameter logistic (4PL) model is fitted to an ELISA standard curve. What advantage does the 4PL provide over a simple linear fit?

47 In an indirect ELISA for detecting anti-viral antibodies in serum, samples from previously vaccinated but uninfected individuals give positive signals. This is best described as:

48 A lab measures the following triplicate OD values for one well set: 0.42, 0.44, and 0.98. Before calculating concentration, the analyst should:

49 Which sequence correctly orders the reagent additions in a standard sandwich ELISA?

50 An ELISA has a limit of detection (LOD) defined as the mean blank signal plus . If the mean blank OD is and the blank standard deviation is , the LOD in OD units is:

51 During ELISA optimization, checkerboard titration is performed. Its primary purpose is to:

52 A researcher switches from a direct ELISA to an indirect ELISA using the same primary antibody. What is the main expected consequence?

53 Two anti-target antibodies are being evaluated as a capture/detection pair for a sandwich ELISA. Which property is most critical for them to function together?

54 A serum sample gives an OD of . From a 4PL standard curve, this corresponds to . The sample was diluted before assay. The concentration in the original undiluted serum is:

55 Why does inadequate washing between ELISA steps typically increase background rather than decrease specific signal?

56 In assay validation, an ELISA shows 95% sensitivity and 80% specificity. In a population where disease prevalence is only 2%, what is the main practical concern with a positive result?

57 Biotin-streptavidin systems are frequently incorporated into ELISA detection. The main rationale is that:

58 An ELISA plate reader corrects readings using a reference wavelength (e.g., 570 nm subtracted from 450 nm). The purpose of this dual-wavelength correction is to:

59 A researcher wants to detect a conformational epitope that is destroyed by drying antigen onto the plate. The most appropriate ELISA design modification is:

60 The intra-assay coefficient of variation (CV) of an ELISA is calculated from replicate wells as . If replicate ODs have mean and standard deviation , the CV is: