Western Blot Protocols

Western Blot (WB) Protocol for High Molecular Weight and Low-Abundance Proteins

An optimized workflow for resolving and detecting challenging protein targets.

Western blotting (WB) is a widely used technique for detecting specific proteins and estimating their molecular weight in cell or tissue extracts. However, high molecular weight (HMW) proteins and low-abundance targets present additional challenges, including inefficient gel resolution, incomplete transfer, and weak signal detection. This protocol describes an optimized WB workflow designed to improve resolution and transfer of HMW proteins while maximizing detection sensitivity for low-expressing targets.

Materials

Buffers & Solutions

Store all buffers at 4°C

  • 2× Laemmli Sample Buffer (50 ml)
    ○ 0.5 M Tris-HCl (12.5 ml, pH 6.8)
    ○ 4% SDS (10 ml from 20% stock)
    ○ 20% Glycerol (10 ml)
    ○ 0.01% 2-Mercaptoethanol (5 µl)
    ○ 0.016% (w/v) Bromophenol Blue (2 mg)
    ○ Complete volume with ddH₂O (17.49 ml)

  • 10× Running Buffer (2 L)
    ○ 247.6 mM Tris-base (60 g)
    ○ 1.92 M Glycine (288 g)
    ○ 4% SDS (100 ml from 20% stock)
    ○ ddH₂O to a final volume of 2 L

  • 5× Transfer Buffer (2 L)
    ○ 154.8 mM Tris-base (37.5 g)
    ○ 1.2 M Glycine (180 g)
    ○ 2.5% SDS (62.5 ml from 20% stock)
    ○ ddH₂O to a final volume of 2 L

  • Blocking Solution
    ○ 1× PBS (prepared from stock: PBSX20-1L, BioPrep Ltd)
    ○ 3% BSA
    ○ 0.05% Sodium Azide (NaN₃)

  • Primary Antibody Dilution Buffer
    ○ 1× PBS
    ○ 1% BSA
    ○ 0.1% Tween-20
    ○ 0.05% NaN₃

  • Washing Buffer
    ○ 1× PBS
    ○ 0.1% Tween-20

  • Secondary Antibody Dilution Buffer
    ○ 1× PBS
    ○ 1% BSA
    ○ 0.1% Tween-20
    ○ SuperSignal™ West Pico PLUS Chemiluminescent Substrate (TS-34578, Thermo Scientific™)


 

Additional Reagents

  • Primary antibody of choice (refer to Alomone catalogue to find the antibody suited for you: Primary Antibodies)
  • Goat Anti-Rabbit IgG-Horseradish Peroxidase antibody (1706515, BioRad)

  • SDS-PAGE gel (commercial or homemade)
  • Stain All Dye (SALL-500, Alpha Diagnostics)

 

Other

  • Heating block or water bath
  • Power supply for electrophoresis and transfer
  • Nitrocellulose membrane for transfer (10401387, Tamar ltd.)
  • Rocking platform
  • Imaging system (chemiluminescence)

Procedure

Step 1 - Sample Preparation and Denaturation

Proper sample preparation and denaturation ensure accurate protein separation and detection. For cell line samples or tissue samples refer to our linked protocols.

1.1 Mix samples

  • In a 1:1 ratio with 2× Laemmli Sample Buffer.
    ⏱ Heat for 10 minutes at 70-100°C.
  • Briefly spin down and cool.

1.2 Load the samples into gel wells

  • 80–100 µg tissue lysate per lane, or
  • Lysate from 2–5 × 10⁵ cells per lane.

1.3 Positive controls

  • We recommend using western blot positive controls to avoid misinterpretation of results. Refer to Alomone’s Positive Control catalogue.
  • Process the positive control under the same conditions as the sample; do not heat above 70 °C.


Step 2 - SDS-PAGE

2.1 Assemble gel 

  • According to manufacturer guidelines.
  • Low-percentage and gradient gels are recommended for high-molecular-weight proteins and low-abundance proteins.
    Recommended gel types:
    ○ Tris-Glycine, 4-6%
    ○ Tris-Acetate, 3-8%
    Optimal gel percentage should be determined empirically.

2.2 Fill tank with 1 × Running buffer, (diluted 1:10 from 10 × stock in ddH₂O).

2.3 Run electrophoresis until dye front reaches the bottom (conditions depend on gel percentage).


Step 3 - Protein Transfer

Choose wet transfer for maximum efficiency when dealing with large-size proteins or low abundant proteins.

3.1 Prepare 1× Transfer Buffer (from 5× stock) as follows:

  • 200 ml methanol (100%)
  • 200 ml 10× Running Buffer
  • 600 ml ddH₂O

Mix thoroughly and chill to 4 °C.

3.2 Transfer to nitrocellulose membrane

⏱ 100 mA for ~20 hours at 4°C.
Extended transfer times significantly improve recovery of high molecular weight proteins.


Step 4 - Blocking

Prevents non-specific antibody binding by saturating free sites on the membrane, ensuring cleaner and more specific signal detection.

4.1 Incubate membrane in Blocking Solution

⏱ 2–5 hours at RT, gentle agitation.


Step 5 - Primary Antibody Incubation

5.1 Primary antibody dilution

  • Dilute in Primary Antibody Dilution Buffer according to the recommended dilution.

5.2 Incubate

⏱ incubate for 2-3 hours at RT or overnight at 4°C for enhanced sensitivity.
Negative control, e.g. blocking peptide, is recommended to avoid misinterpretation of results. Refer to Alomone’s Negative Control catalogue and protocols.

5.3 Wash

  • Rinse membrane with washing buffer.
    ⏱ 10 min. × 3 at RT.


Step 6 - Secondary Antibody Incubation

From this step forward, do not use buffers containing sodium azide when working with HRP-conjugated antibodies.

6.1 Secondary antibody dilution

  • Dilute the secondary antibody according to the manufacturer instructions, in Secondary Antibody Dilution Buffer.

6.2 Incubate

⏱ incubate for 1 hour at RT with gentle agitation.
     
6.3 Wash

  • Rinse membrane with washing buffer.
    ⏱ 10 min. × 3 at RT.


Step 7 - Detection

7.1 ECL reagents preparation

  • Prepare according to manufacturer’s instructions.

7.2 Incubate

  • Ensure the solution fully covers the membrane and incubate for the time recommended by the manufacturer.

7.3 Visualize protein

  • Use film or a digital imaging system.
  • Exposure time will vary by protein abundance and detection reagent.

Troubleshooting and Tips

Problem Possible Cause Solution
Weak or no signal Low antibody concentration; poor transfer; degraded sample Increase primary antibody concentration; Extend transfer time; use lower-percentage gels; use fresh lysates with protease inhibitors; verify protein transfer staining membrane with Stain-All Dye.
High background Insufficient blocking; excessive concentrated antibodies; inadequate washing Extend blocking time; use 3% BSA instead of milk for membrane proteins; increase antibody dilution; add extra washing steps.
Uneven bands Gel polymerization issues; air bubbles under membrane Use fresh gels; remove all bubbles during transfer setup.
Smearing Overloading samples; salt or detergent contamination; proteolysis Reduce sample load; clean up lysates (e.g., desalting); add protease inhibitors; avoid freeze–thaw cycles.
Non-specific bands Off-target binding; too much primary antibody Increase primary antibody dilution; include blocking peptide or use more stringent washes.
Incomplete transfer of proteins Insufficient transfer time; percentage too high; membrane pore size too small Increase transfer time; use lower-percentage gels; switch to PVDF with 0.45 µm or 0.2 µm pore size for very large proteins.
Weak ECL signal Old or expired chemiluminescent substrate; low HRP activity Use fresh ECL reagents; avoid sodium azide with HRP antibodies; reduce exposure to light during preparation.
Membrane staining shows no large proteins Stain All Dye is less sensitive to HMW proteins; large proteins may transfer weakly Use stronger stains such as Revert 700, MemCode, or Amido Black to verify transfer of “difficult” targets.

Example Data

 

Expression of the α1B-adrenoceptor in GH3 cells. Cell surface detection of α1B-adrenoceptor in living GH3 cells. The cells were stained with Anti-α1B-Adrenergic Receptor (extracellular) Antibody (AAR-018) (1:100) followed by staining with goat anti-rabbit Alexa Fluor 488 secondary antibody (green). The cell nuclei were stained with the DNA dye Hoechst 33342 (blue).

Expression of the noradrenaline transporter (NET) in live intact rat pheochromocytoma (PC12) cells. Cell surface detection of NET in live intact rat PC12 cells. The cells were stained with Anti-Noradrenaline Transporter (extracellular) Antibody (AMT-002) (1:100) followed by staining with goat anti-rabbit Alexa Fluor 594 secondary antibody (red). The cell nuclei were visualized using the cell-permeable DNA dye Hoechst 33342 (blue).