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ExKits ELISA Kits FAQ & Troubleshooting
1
High Background or Non-specific Binding
Q1: Why is there high background or non-specific binding in my ELISA results?
A: After adding stop solution, the entire plate shows uniform yellow or pale yellow, or the standard curve is linear but with excessively high background. This can be caused by using mismatched reagents or mixed kits/batches, insufficient plate washing, overly long incubation or color development time, contamination of pipette tips, substrate containers, or wells by HRP conjugates or positive controls, excessively high concentration of detection antibody or HRP-avidin, TMB substrate exposed to light or contaminated before use, or incorrect microplate reader wavelength settings.
Solutions:

    Always verify reagent labels and lot numbers before the assay; only use reagents from the same ExKits kit.

    Maintain consistent wash buffer volume per well and tap the plate dry on absorbent paper after washing.  

    Strictly follow the kit protocol for incubation and color development time.

    Change tips between reagents and use separate vessels for different solutions.

    Check dilution calculations and dilute detection antibody or HRP-avidin further if needed.

    Keep TMB substrate protected from light until use.

2
No Color Development
Q2: Why is there no color development in any wells, including the positive control?
A: No color development after the substrate reaction usually results from incorrect or mixed reagents, or omitted reagents or skipped procedural steps.
Solutions:

    Double-check reagent labels during preparation and handling. 

    Ensure all wash buffer containers are clean and contamination-free.

    Carefully read the operating protocol and strictly follow the reaction sequence specified in the instructions.
3
Weak Signal Development
Q3: What causes weak color signal in both standard and sample wells?
A: Overall faint color development can be attributed to expired kit or improper storage, reagents and samples not equilibrated to room temperature (18–25°C) for 30 minutes before use, inaccurate pipetting, fast liquid handling, or dirty/reused tips, insufficient incubation or color development time, improper wash buffer dilution or excessive washing cycles, or low-quality or contaminated distilled water for buffer preparation.
Solutions:

    Confirm validity and store ExKits kits under recommended conditions to avoid contamination.

    Equilibrate all reagents and samples at room temperature before use.

    Use calibrated pipettes with proper, single-use tips.

    Use a timer; typical color development is 15–30 minutes.

    Dilute concentrate as directed and control washing volume and frequency.

    Use pure, neutral water for buffer preparation.
4
Poor Standard Curve & Repeatability
Q4: What leads to poor repeatability and unstable standard curves?

A: Poor well-to-well consistency may arise from improper standard dilution, premature preparation of working reagents, insufficient mixing after sample addition, inconsistent incubation, washing, or coloration conditions, unstable incubation temperature, cross-contamination or reused consumables, scratches, dirt, or fingerprints on the plate bottom, clogged washer heads or insufficient sample centrifugation, or sample degradation or contamination.

Solutions:

    Use only the recommended diluent and follow ExKits guidelines.

    Prepare working solutions 10 minutes before use.

    Mix thoroughly and handle plates gently to prevent splashing.

    Keep parameters uniform across experiments.

    Maintain a constant 37°C environment.

    Replace tips and use separate reservoirs for each reagent.

    Avoid touching the bottom and wipe gently before reading.

    Clear washer nozzles and centrifuge samples fully.

    Use fresh samples or store at low temperatures.

    When pipetting samples, take care to avoid generating air bubbles.

    Weather conditions vary by region. Be sure to eliminate static electricity before operation to prevent enlarged      differences in reaction liquid levels between wells.

5
General Product & Usage FAQ
Q5: What quality control tests does ExKits perform on each ELISA kit?
A: Every ExKits ELISA kit is rigorously evaluated for linearity range, linearity, limit of detection, precision, recovery, stability, specificity, and performance with natural samples under strict QC standards to ensure reliable performance.
Q6: Do ExKits ELISA kits include standards or controls?
A: Qualitative kits include positive and negative controls. Quantitative kits provide calibrated standards that also function as internal quality controls. Standards are fully matched with the reagent system, and duplicate wells are strongly recommended.
Q7: What species are ExKits ELISA kits compatible with? Can they be used for unlisted species?
A: ExKits ELISA kits support a wide range of species including human, mouse, rat, rabbit, bovine, porcine, canine, chicken, fish, monkey, and more. Antibody specificity and matrix effects vary by species. Contact us for assistance in selecting the appropriate kit.
Q8: How many replicates should I run for standards and samples?
A: Duplicate wells are recommended for both standards and samples to improve accuracy and reliability.
Q9: Can I mix reagents from different ELISA kits? Can I purchase individual components?
A: Reagents from different kits or different batches should not be interchanged. ExKits does not sell individual components such as standards or antibodies separately.
Q10: Do ExKits kits contain BSA and preservatives? What is the stop solution?
A: Selected components contain BSA. Proclin 300 is used as a preservative, and most kits use 2N sulfuric acid as the stop solution.
Q11: Can incubation be performed at room temperature?
A: Except for food safety and drug residue kits, all ExKits ELISA kits recommend incubation at 37°C for optimal antigen-antibody binding. Room temperature is not recommended due to instability.
Q12: What is TMB?
A: TMB (3,3',5,5'-Tetramethylbenzidine) is a chromogenic substrate for horseradish peroxidase. After adding stop solution, the color changes from blue to yellow, measured at 450 nm. 
Q13: What is ELISA and what is the standard workflow?
A: ELISA stands for Enzyme-Linked Immunosorbent Assay, used to detect and quantify specific proteins. Common formats include sandwich, competitive, and indirect ELISA. The general procedure includes reagent preparation, sample/reagent addition, incubation, washing, color development, and reading.
Q14: Are ExKits ELISA plates pre-coated? How should I store unused strips?
A: Yes, plates are pre-coated with capture antibody. Unused strips can be separated and stored at 2–8°C in the dark, free from microbial contamination.
6
Special Phenomenon Explanations
Q15: Why is my standard curve normal but sample wells show weak color?
A: Interfering substances may be present in the sample, which can affect antigen-antibody binding. In addition, certain destructive components, such as strong surfactants and strong denaturants like SDS, may damage the antibody structure. Repeat testing is generally recommended to rule out operational interference.
Q16: Why does the microplate reader give low readings even when color looks normal visually?
A: This is typically caused by incorrect filter selection. For TMB-based detection, set the measurement wavelength to 450 nm with a 650 nm reference wavelength.
Q17: What causes random abnormal wells and drifting absorbance values?
A: Abnormal wells often come from cross-contamination during plate blotting, blocked liquid dispensing heads in the plate washer, incomplete sample centrifugation leading to well coagulation or particulate interference, contaminated or degraded samples due to prolonged storage, or improperly prepared wash buffer or use of undiluted concentrate.
Problem DescriptionPossible CauseSolution
Whole plate yellow or high backgroundWrong reagents or mixed batchesUse same ExKits kit, check lot numbers
No color in any wellsEnzyme conjugate inactivationKeep containers clean, avoid contamination
Weak color in all wellsReagents not equilibrated to room temperatureEquilibrate 30min at 18-25°C
Poor repeatabilityInconsistent washing or incubationKeep conditions uniform each test
Low reader reading but normal colorWrong wavelength filterUse 450nm
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