Common Troubleshooting Tips for Western Blot Results

Q1: Why do I need both positive and negative control lysate?

How can I choose these two?

A: They have different functions: Positive control lysate demonstrates that the staining protocol is successfully performed and gives the expected level of sensitivity/specificity as characterized during technical optimization, while negative control lysate checks for non-specific binding. (false-positive results) Proper selection and interpretation of these controls rely on a thorough understanding how protein transfer occurs, how protein bands form during the assay, and how detection relates to the behavior of the protein of interest. Including a loading control further strengthens interpretation by confirming consistent protein levels across samples.

For consistent and reproducible outcomes, especially when working with complex or variable samples, consider utilizing a reliable Western Blotting Service that can provide expert handling across all stages of the protocol or check our western blotting technique principle, including how proteins are transferred, detected, and analyzed within the method's workflow.

Commonly used positive controls include:

  • Overexpression samples
  • reporter cell lines with high protein of interest levels
  • Purified recombinant protein

Commonly used negative controls include:

  • Samples from knockdown or knockout tissue/cell lines
  • Samples from RNA interference targeted lines

Table. Established controls for Western Blot

For a deeper understanding of common issues and their solutions, explore this comprehensive western blot troubleshooting guide.

Types of WB ControlsCharacteristics
Positive control lysateLysate from a cell line or tissue sample (from a tested species) known to express the target protein
  • Demonstrate that the staining protocol is successfully performed and giving the expected level of sensitivity/specificity as characterized during technical optimization
  • Confirms that negative results are accurate
  • Commonly used positive controls:
    • Samples from cells exhibiting overexpression of target protein
    • Cell line/tissue/experimental condition with a proven positive signal
    • Purified recombinant protein
Negative control lysateLysate from a cell line or tissue sample known not to express the target protein
  • Check for non-specific binding (false-positive results)
  • Commonly used negative controls:
    • Samples from knockdown or knockout tissue/cell lines
    • Samples from RNA interference targeted lines
    • Cell line/tissue/experimental condition with proven negative signal

Q2: What Causes Differences Between Detected and Theoretical

Molecular Weight, and How to Address Them?

A: Compared to theoretical molecular weight, molecular weight has three dimensions to change: increase, decrease, shift due to several factors. Including molecular weight markers or a protein ladder during separation helps verify size accuracy on the SDS-Page gel.

Molecular Weight increase may be caused by these factors:

1: Post-translational modifications (PTMs): Modifications like phosphorylation or glycosylation can increase a protein's molecular size.

Solution: Analyze the protein using deglycosylation enzymes or phosphatase to confirm PTMs.

2: Protein Refolding and Multimerization: Denatured proteins may refold and form dimers, trimers, or tetramers, resulting in molecular weights that are two, three, or four times the monomer size.

Solution: Apply heat, detergents, and appropriate reducing agents during SDS-PAGE to break down multimers.

Molecular Weight decrease may be caused by these factors:

1: Protein Cleavage After Activation: Many proteins are synthesized as precursors and cleaved into active fragments, leading to a smaller actual molecular weight.

Solution: Use specific antibodies targeting precursor and active forms to verify cleavage.

2:Protein Degradation: Partial degradation of proteins can produce fragments with lower molecular weights.

Solution: Use protease inhibitors and phosphatase inhibitors during sample preparation to prevent degradation. Proper western blot sample preparation is essential to minimize degradation risks and ensure accurate protein detection.

Other reasons for molecular weight shifts:

In some cases, the molecular weight may change to a specific number:

1: Differences in Apparent and Theoretical Molecular Weight: Some proteins, such as p53, have an apparent molecular weight (e.g., 53 kDa, from which its name derives) that differs from the theoretical value calculated from its amino acid sequence (e.g., 43 kDa for p53).

Solution: Verify molecular weight discrepancies by cross-referencing with literature or databases.

2: Multiple Isoforms: Many proteins exist in various isoforms, each with a different molecular weight.

Solution: Confirm the isoform using isoform-specific antibodies or mass spectrometry.

Q3: What causes the high background in my western blot results and how can I solve it?


A: Here are some common possible causes and suggestions.

1: Inadequate Membrane Blocking

Solution: Extend the blocking time or choose a more suitable blocking buffer.

2: Inappropriate Primary Antibody Dilution

Solution: Perform gradient testing to find the optimal antibody dilution and reduce antibody concentration.

3: High Primary Antibody Incubation Temperature

Solution: Incubate at 4°C overnight.

4: Overexposure During Detection

Solution: Shorten exposure time during chemiluminescent detection using a high-quality chemiluminescent substrate.

5: Insufficient Membrane Washing

Solution: Increase the washing time or wash the membrane more frequently.



Q4: What causes the multiple non-specific bands (blotchy patterns) in western blot results and how can I solve it?


A: Here are some common possible causes and suggestions.

1: Target Protein Has Multiple Modification Sites (e.g., Phosphorylation, Glycosylation, Acetylation):

Solution: Review the literature or conduct bioinformatics analysis to identify modification sites. Remove modifications to confirm the protein's true size.

2: Target Protein Has Alternative Splicing Variants:

Solution: Consult literature or perform bioinformatics analysis to determine the possibility of splicing variants.

3: Degradation of Target Protein During Sample Preparation:

Solution: Use protease inhibitors and handle samples on ice.

4: Excessive Loading Amount or High Sensitivity:

Solution: Reduce the sample loading amount appropriately.

5: High Concentration of Primary or Secondary Antibody:

Solution: Lower the antibody concentration.


Q5: What causes No Signal or Weak Signal in Western Blot Results and How to solve it?

  1. Target Protein is Not Expressed in the Sample
    Solution: Use positive control lysates from cells with high protein expression to confirm whether the test sample is negative.

  2. Low Target Protein Expression
    Solution: Increase sample loading volume and ensure protease inhibitors are added to the lysis buffer. Concentrate the sample to maximize signal detection. For nuclear proteins, use nuclear extraction buffer; for membrane proteins, use membrane lysis buffer. Induce target protein expression through treatments like drugs or other specific conditions to bring protein levels within the detectable range. In some cases, you may also consider alternative detection methods such as the in-cell western blot, which allows quantification of target proteins directly within intact cells, offering improved sensitivity for low-abundance proteins and minimizing sample loss during preparation.

  3. Target Protein is Secreted
    Solution: Use Brefeldin A (BFA) to inhibit protein secretion and extract whole-cell lysates. Alternatively, extract proteins from the culture supernatant if they are not detected in the lysate.

  4. Insufficient Lysis
    Solution: Use sonication to enhance protein release. Always sonicate samples after adding lysis buffer, especially for nuclear proteins.

  5. Incomplete or Overtransfer
    Solution: Verify using Ponceau S staining, Ponceau staining, or Coomassie staining. Ensure Polyvinylidene difluoride membranes are pre-soaked in methanol. Review Transfer Conditions and ensure consistent semi-dry transfer performance. Check the transfer sandwich assembly for trapped air bubbles and ensure proper use of Blotting Papers.

  6. Cross-Reactivity Between Blocking Agent and Antibodies
    Solution: Use mild detergents like Tween-20 or switch to an alternative blocking agent, such as non-fat milk, BSA, or serum.

  7. Antibody Fails to Recognize the Target Species
    Solution: Confirm cross-reactivity with the species being tested by reviewing the antibody datasheet before purchase.

  8. Insufficient Binding of Primary or Secondary Antibodies
    Solution: Increase antibody concentration and extend incubation time at 4°C (e.g., overnight).

  9. Mismatch Between Primary and Secondary Antibodies
    Solution: Use a secondary antibody specific to the host species of the primary antibody.

  10. Azide Inhibition of Secondary Antibody
    Solution: Avoid using azide with HRP-conjugated antibodies.

  11. Overwashing the Membrane
    Solution: Avoid excessive washing of the membrane.

  12. Expired Reagents or Inactive Substrate
    Solution: Use fresh detection reagents.


Q6: What causes Uneven Band Intensity in

Western Blots and How to solve it?

Uneven band intensity may result from inconsistent antibody-protein binding efficiency or uneven protein level.

Solution: Adjust antibody concentration, optimize incubation time, and improve protein extraction and quantification methods.


Q7: What causes Skewed or Shifted Bands in

Western Blot and How to solve it?

If band distortion is not caused during electrophoresis, possible reasons include:

  1. Improper Sandwich Assembly: Long-term use of transfer device components like sponge pads may cause thinning, or inadequate compression during assembly can create gaps between the gel and membrane. This may lead to protein loss or membrane skewing during transfer.
  2. Insufficient Transfer Buffer: Ensure that the gel and membrane are fully immersed in transfer buffer during the process.