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.

Key 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 contaminatedUse 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.
2.Reaction not stoppedColour will keep developing if the substrate reaction is not stopped.
3.Plate left too long before reading on the plate readerColour will keep developing (though at a slower rate if stop solution has been added)
4.Contaminants from laboratory glasswareEnsure reagents are fresh and prepared in clean glassware
5.Substrate incubation carried out in the lightSubstrate 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 washedWash wells as per protocol recommendations.
7.Too much detection reagent addedEnsure 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 buffersIncreasing salt concentrations may reduce non-specific and/or weak off-target interactions.
10.High antibody concentrationTry different dilutions for optimal results.
11.Precipitate formed in wells upon substrate additionIncrease dilution factor of sample or decrease concentration of substrate.
12.Dirty plateClean 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 buffersAlways make fresh buffers

 

ELISA Troubleshooting for

Out of Range

17.Samples contain no or below detectable levels of analyteIf 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 pointSamples may require further dilution
19.Insufficient washingUse 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 reusedDuring 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 preparedCheck 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 blueSubstrate solution should be mixed and used immediately
24.too much streptavidin-HRPCheck dilution, titrate if necessary
25.Plate sealers or reagent reservoirs reused, resulting in presence of residual HRP. This will turn the TMB blue non-specificallyUse fresh plate sealer and reagent reservoir for each step
26.Buffers contaminated with metals or HRPMake fresh buffers

ELISA Troubleshooting for

High Variation

27.Multichannel pipette errorsCalibrate the pipettes
28.Plate washing was not adequate or uniformMake sure pipette tips are tightly secured. Confirm all reagents are removed complete in all wash steps
29.Non-homogenous samplesThoroughly mix samples before pipetting
30.Samples may have high particular matterRemove the particulate matter by centrifugation
31.Insufficient plate agitationThe 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 contaminationWhen 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 incubationsStacking 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 mixedTo ensure a consistent concentration across all wells, ensure all reagents and samples are mixed before pipetting onto the plates.
36.Well allowed to dry outEnsure 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 dirtyClean the bottom of the plate carefully before re-reading the plates
38.Bubbles in wellsEnsure no bubbles are present prior to reading the plate
39.Edge effectsEnsure the plate and all reagents are at room temperature
40.StorageEnsure reagents and samples are stored are correct temperature
41.Capture antibody didn’t bind to the plateEnsure 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 protocolsAdhere to the protocol that comes with your  assay
43.Improper calculations of standard curveCheck calculations, make new standard curve & use internal controls
44.Buffers contaminatedUse fresh buffers
45.Well bottom scrappedAvoid 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 washesIncrease number of washes. Increase soaking time between washes prior to addition of substrate solution.
49.Cross-ReactivityDetection antibody cross-reacting with coating antibody. Run appropriate controls.
50.Non-specific binding of antibodiesEnsure 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 highPerform dilutions to determine optimal working concentration.
52..Incorrect assay temperatureCheck that the incubation temperature did not exceed 37°C
53.Inadequate washingEnsure 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 sampleTest sample with substrate alone to check for contaminating enzyme activity.
55.Wells are insufficiently washedWash wells are per protocol recommendations.
56.Contaminated wash bufferPrepare fresh buffers
57.Too much detection reagentEnsure the reagent has been diluted properly or decrease the recommended concentration of detection reagent
58.Blocking buffer ineffectiveTry different blocking buffer reagent and/or add blocking reagent to wash buffer
59.Salt concentrations of incubation/wash buffersIncreasing salt concentrations may reduce non-specific and/or weak off target interactions.
60.Waiting too long to read plate after addition of stop solutionRead plate immediately after adding stop solution
61.High antibody concentrationTry different dilutions of optimal results
62.substrate incubation is carried out in lightSubstrate incubations should be carried out in the dark or as recommended by manufacturer.
63.Precipitate formed in wells upon substrate additionIncrease 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 addedadd appropriate detection antibody and continue
66.Avidin-HRP was not addedAdd avidin-HRP according to protocol and continue
67.substrate solution was not addedadd substrate solution and continue
68.wash buffer contains azideAvoid sodium azide in the wash buffer
69.Incubation time too shortIncubate samples overnight at 4’C or follow manufacturers guidelines
70.Target present below detection limits of assayDecrease dilution factor or concentrate samples
71.Incompatible sample typeDetection 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 plateTo 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 incompatibilityEnsure assay buffer is compatible with the target of interest (e.g. enzymatic activity retained, protein interactions retained.)
74.Not enough detection reagentIncrease concentration of amount of detection reagent following manufacturer guidelines
75.Sample prepared incorrectlyEnsure proper sample preparation/dilution. Samples may be incompatible with microtiter plate assay format
76.Insufficient antibodyTry different concentrations/dilutions of antibodies
77.Incubation temperature is too lowEnsure 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 wavelengthVerify the wavelength and read the plate again
79.Plate washing is too vigorousCheck the correct pressure in the automatic plate washer. Pipette wash buffer gently if washes are done manually.
80.Wells dried outDo 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 reactionsPrepare 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 ReagentsEnsure all reagents used are within date
85.

 

 

 

 

Assay format not sensitive enoughSwitch 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 antibodiesRe-evaluate reagents used.

 ELISA Troubleshooting for

Poor standard curve

87.standard was incompletely reconstituted or was incorrectly storedReconstitute standard according to the protocol provide and follow storage instructions
88.Reagents were added to the wells at incorrect concentrationsCheck for pipetting errors and correct the reagent volume
89.incubations done at incorrect temperatureFollow protocol for storage, incubation and agitation
90.Wells not completely aspiratedCompletely aspirate between steps, use plate wash where possible
91.Plates stacked during incubationKeep plates separated
92.Poor dilution seriesCheck dilution steps according to protocol
93.Reagents poorly mixedMake sure to mix reagents thoroughly
94.Poor or variable adsorption of reagents to plateCheck 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 degradedCheck that standard was stored correctly
96.Curve doesn’t fit scaleTry plotting use different scales, e.g. log-log, 5 parameter logistic curve fit
97.Pipetting errorCheck pipettes and calibrate
98.Capture antibody didn’t bind to the plateEnsure that you are using and ELISA plate, not a tissue culture plate.
99.Not enough detection antibodyCheck dilution, titrate if necessary
100.

 

Incorrect calculation of standard curve dilutionCheck your calculations and make a new curve.
101.Mixing or Substituting reagents from different kitsAvoid this as it can affect the quality of your assay