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101 ELISA Troubleshooting Tips

101 ELISA Troubleshooting Tips

Our 101 ELISA troubleshooting tips guide is designed to help you improve and troubleshoot the common problems that researchers have with their ELISA kits when performing assays. Optimising your ELISA and removing common mistakes that are made can dramatically improve your results and the sensitivity of your ELISA assays. In this ELISA troubleshooting guide we have detailed the common areas where researchers encounter problems with their ELISA.

ELISA Troubleshooting areas

High Signal:

High Signal can occur for numbers reasons including insufficient plate washing, not stopping the reaction and adding too much detection reagent. If you have a high signal this can results in a lot of false positives and incorrect data.

Out of Range:

Sometimes this can happen based on your samples, insufficient washing or incorrect dilutions prepared. This can result in a loss of data due to negative or no results.

High Variation:

High variation can be due to sample preparation mistakes, pipette errors and inconsistencies, insufficient plate agitation among other problems. Data with high variation can skew the real results and cause inconsistencies in your data.

Background is high

High background may result from inadequate washing steps, cross reactivity of samples or contamination. Again high background may result in false positive/negative data and affect your results.

No Signal

No signal in your ELISA assay may result from numerous sample and assay problems including wash buffer contains azide, target below detection of assay or avidin-HRP was not added. No signal may mean no results from precious samples, have a read through the reasons below to avoid these problems.

Poor Standard Curve

A poor standard curve will prove unpublishable results if not prepared correctly. Reasons may included reagents are poorly mixed, the standard has degraded or pipetting errors.

ELISA troubleshooting for High Signal

1.

TMB Substrate Solution was contaminated

Use fresh TMB substrate solution which should be clear and colorless prior to addition to wells. Use a clean V bottom container prior to pipetting substrate solution into wells. Use a clean V bottom container prior to pipetting substrate solution into wells.

2.

Reaction not stopped

Colour will keep developing if the substrate reaction is not stopped.

3.

Plate left too long before reading on the plate reader

Colour will keep developing (though at a slower rate if stop solution has been added)

4.

Contaminants from laboratory glassware

Ensure reagents are fresh and prepared in clean glassware

5.

Substrate incubation carried out in the light

Substrate incubation should be carried out in the dark. Ensure substrate is not exposed to light—store in a dark place. Limit exposure to light while running assay.

6.

Wells are insufficiently washed

Wash wells as per protocol recommendations.

7.

Too much detection reagent added

Ensure the reagent has been diluted properly or decrease the recommended concentration of detection reagent.

8.

Blocking buffer ineffective (e.g. detection reagent binds blocker; wells not completely blocked)

Try different blocking reagent and/or add blocking reagent to wash buffer.

9.

Salt concentration of incubation/wash buffers

Increasing salt concentrations may reduce non-specific and/or weak off-target interactions.

10.

High antibody concentration

Try different dilutions for optimal results.

11.

Precipitate formed in wells upon substrate addition

Increase dilution factor of sample or decrease concentration of substrate.

12.

Dirty plate

Clean the bottom of the plate.

13.

Incorrect standard curve dilutions
prepared

Check your pipetting technique. Calibration of pipettes might be required.

14.

Longer incubation times than
recommended

Make sure your incubation times are correct and adhere to the protocol provided with the technical manual.

15.

Plate sealers or reagent reservoirs reused, resulting in presence of residual HRP. This will turn the TMB blue non-specifically

Reuse of plate sealers may lead to the presence of residual HRP, leading to non- specific colour change of TMB. To avoid this use fresh plate sealer and reagent reservoir for each step.

16.

Contamination of buffers

Always make fresh buffers.


ELISA Troubleshooting for out of Range

17.

Samples contain no or below detectable levels of analyte

If samples are below detectable levels, it may be possible to use high sample volume. Check with technical support for appropriate protocol modifications.

18.

Samples contain analyte concentrations higher than the highest standard point

Samples may require further dilution

19.

Insufficient washing

Use appropriate washing procedure—see below. At the end of each washing step, invert plate on absorbent tissue and allow to completely drain, tapping forcefully if necessary to remove any residual fluid.

20.

Plate sealers not used or reused

During incubations, cover assay plates with plate sealers. Use a fresh sealer each time the plate is opened. This will prevent wells from contaminating each other.

21

Incorrect dilutions prepared

Check pipetting technique—see below—and double-check calculations.

22.

Longer incubation times than
recommended

Manufactured kits have optimized protocols. Make sure to follow recommended incubation times. If developing ELISA using antibody pairs you may need to optimize the assay. See ELISA Development and Optimization for more information.

23.

Substrate solution mixed too early and turned blue

Substrate solution should be mixed and used immediately

24.

Too much streptavidin-HRP

Check dilution, titrate if necessary

25.

Plate sealers or reagent reservoirs reused, resulting in presence of residual HRP. This will turn the TMB blue non-specifically

Use fresh plate sealer and reagent reservoir for each step

26.

Buffers contaminated with metals or HRP.

Make fresh buffers


ELISA Troubleshooting for High Variation

27.

Multichannel pipette errors

Calibrate the pipettes

28.

Plate washing was not adequate or uniform

Make sure pipette tips are tightly secured. Confirm all reagents are removed complete in all wash steps

29.

Non-homogenous samples

Thoroughly mix samples before pipetting

30.

Samples may have high particular matter

Remove the particulate matter by centrifugation

31.

Insufficient plate agitation

The plate should be agitated during all incubation steps using an ELISA plate shaker at a speed where solutions in wells are within constant motion without splashing

32.

Cross well contamination

When reusing plate sealers check that no reagent has touched the sealer. Care should be taken when using the same pipette tips used for reagent additions. Ensure that pipette tips do not touch the reagents on the plate.

33.

Plates stacked during the incubations

Stacking of plates does not allow even distribution of temperature across the wells of the plates. Avoid stacking.

34.

Pipette inconsistent

Ensure pipettes are working correctly and are calibrated. Ensure pipette tips are pushed on far enough to create a good seal. Take particular care when diluting down the plate and watch to make sure the pipette tips are all picking up and releasing the correct amount of liquid.

35.

Antibody dilutions/reagents are not well mixed

To ensure a consistent concentration across all wells, ensure all reagents and samples are mixed before pipetting onto the plates.

36.

Well allowed to dry out

Ensure lids are left on the plates at all times when incubating. Place a humidifying water tray (bottled clean/sterile water) in the bottom of the incubator.

37.

Bottom of the plate is dirty

Clean the bottom of the plate carefully before re-reading the plates

38.

Bubbles in wells

Ensure no bubbles are present prior to reading the plate

39.

Edge effects

Ensure the plate and all reagents are at room temperature

40.

Storage

Ensure reagents and samples are stored are correct temperature

41.

Capture antibody didn’t bind to the plate

Ensure that you are using an ELISA plate, not a tissue culture plate. Dilute antibody in PBS. Ensure correct preparation and incubation time for both coating and blocking steps.

42.

Variations in protocols

Adhere to the protocol that comes with your assay

43.

Improper calculations of standard curve

Check calculations, make new standard curve & use internal controls

44.

Buffers contaminated

Use fresh buffers

45.

Well bottom scrapped

Avoid contact with the bottom of the well during pipetting. Aim the pipette tip to the side of the well to avoid disrupting the bottom

ELISA Troubleshooting for Background is high

46.

Background wells were contaminated
Avoid cross-well contamination by using the sealer appropriately. Use multichannel pipettes without touching the reagents on the plate.

47.

Matrix used has endogenous analyte or interference

Check the matrix ingredients for cross reacting components (e.g. interleukin modified tissue culture medium).

48.

Insufficient washes
Increase number of washes. Increase soaking time between washes prior to addition of substrate solution.

49.

Cross-Reactivity

Detection antibody cross-reacting with coating antibody. Run appropriate controls.

50.

Non-specific binding of antibodies

Ensure a block step is included and a suitable blocking buffer is being used. We recommend using 5 to 10% serum from the same species of the secondary antibody, or bovine serum. Ensure wells are pre-processed to prevent nonspecific attachment Use an affinity purified antibody, preferably pre-absorbed

51.

Concentration of conjugated second

antibody too high

Perform dilutions to determine optimal working concentration.

52.

Incorrect assay temperature

Check that the incubation temperature did not exceed 37°C

53.

Inadequate washing

Ensure all wells are filling with wash buffer and are being aspirated completely. Use an automated plate washer if available. Increase number of washes. Add 30 second soak step in-between washes.

54.

Contaminating enzymes present in sample

Test sample with substrate alone to check for contaminating enzyme activity.

55.

Wells are insufficiently washed

Wash wells are per protocol recommendations.

56.

Contaminated wash buffer

Prepare fresh buffers

57.

Too much detection reagent

Ensure the reagent has been diluted properly or decrease the recommended concentration of detection reagent

58.

Blocking buffer ineffective
Try different blocking buffer reagent and/or add blocking reagent to wash buffer

59.

Salt concentrations of incubation/wash buffers

Increasing salt concentrations may reduce non-specific and/or weak off target interactions.

60.

Waiting too long to read plate after addition of stop solution

Read plate immediately after adding stop solution

61.

High antibody concentration

Try different dilutions of optimal results

62.

Substrate incubation is carried out in light

Substrate incubations should be carried out in the dark or as recommended by manufacturer.

63.

Precipitate formed in wells upon substrate addition

Increase dilution factor of sample or decrease concentration of substrate

64.

Dirty plate

Clean the bottom of the plate with a wipe

ELISA Troubleshooting for No Signal

65.

Incorrect or no detection antibody was added
Add appropriate detection antibody and continue

66.

Avidin-HRP was not added
Add avidin-HRP according to protocol and continue

67.

Substrate solution was not added

Add substrate solution and continue

68.

Wash buffer contains azide
Avoid sodium azide in the wash buffer

69.

Incubation time too short

Incubate samples overnight at 4’C or follow manufacturers guidelines

70.

Target present below detection limits of assay
Decrease dilution factor or concentrate samples

71.

Incompatible sample type
Detection may be reduced or absent in untested samples types. Include a sample that the assay is known to detect the positive control

72.

Recognition of epitope impeded by absorption plate

To enhance the detection of a peptide by direct or indirect ELISA, conjugate peptide to a large carrier protein before coating onto a microtiter plate

73.

Assay buffer incompatibility

Ensure assay buffer is compatible with the target of interest (e.g. enzymatic activity retained, protein interactions retained.)

74.

Not enough detection reagent

Increase concentration of amount of detection reagent following manufacturer guidelines

75.

Sample prepared incorrectly

Ensure proper sample preparation/dilution. Samples may be incompatible with microtiter plate assay format

76.

Insufficient antibody

Try different concentrations/dilutions of antibodies

77.

Incubation temperature is too low
Ensure the incubations are carried out at the correct temperature. All reagents including plate should be at room temperature or as recommended by the manufacturer before proceeding.

78.

Incorrect wavelength

Verify the wavelength and read the plate again

79.

Plate washing is too vigorous
Check the correct pressure in the automatic plate washer. Pipette wash buffer gently if washes are done manually.

80.

Wells dried out

Do not allow wells to become dry once the assay has started. Cover the plate using sealing film or tape for all incubations.

81.

Slow colour development of enzymatic reactions

Prepare substrate solution immediately before use. Ensure the stock solution has not expired and is not contaminated. Allow longer incubation.

82.

Uneven Colour

Ensure all wells are washed correctly, use a ELISA plate washer where possible

83.

 

Reagents not at room temperature

All reagents should at room temperature from the start of the assay. Room temperature should be reached following 15–20 minutes on the bench.

84.

Expired Reagents
Ensure all reagents used are within date

85.

Assay format not sensitive enough

Switch to a more sensitive assay type (e.g. direct ELISA to sandwich ELISA). Lengthen incubation times or increase temperature. Or change the detection method

86.

Buffer containing FCS used to reconstitute antibodies

Re-evaluate reagents used.

ELISA Troubleshooting for Poor standard curve

87.

Standard was incompletely reconstituted or was incorrectly stored

Reconstitute standard according to the protocol provide and follow storage instructions

88.

Reagents were added to the wells at incorrect concentrations

Check for pipetting errors and correct the reagent volume

89.

Incubations done at incorrect temperature
Follow protocol for storage, incubation and agitation

90.

Wells not completely aspirated

Completely aspirate between steps, use plate wash where possible

91.

Plates stacked during incubation

Keep plates separated

92.

Poor dilution series
Check dilution steps according to protocol

93.

Reagents poorly mixed
Make sure to mix reagents thoroughly

94.

Poor or variable adsorption of reagents to plate

Check choice of coating buffer, usually PBS with a pH of 7.4 or carbonate bicarbonate buffer pH 9.6. Try extending this incubation time or consider using different plates

95.

Standard degraded

Check that standard was stored correctly

96.

Curve doesn’t fit scale

Try plotting use different scales, e.g. log-log, 5 parameter logistic curve fit

97.

Pipetting error

Check pipettes and calibrate

98.

Capture antibody didn’t bind to the plate

Ensure that you are using and ELISA plate, not a tissue culture plate.

99.

Not enough detection antibody

Check dilution, titrate if necessary

100.

Incorrect calculation of standard curve dilution

Check your calculations and make a new curve.

101.

Mixing or Substituting reagents from different kits

Avoid this as it can affect the quality of your assay

ELISA Troubleshooting & Tips