Bench protocol
Western blot protocol: complete workflow from sample to quantification
This guide covers a conventional denaturing Western blot. Product-specific instructions for the antibody, gel, membrane, transfer device and imaging system take priority where they differ from the general conditions below.
Before you start
- ✓Target and expected apparent molecular weight, including known isoforms or processing.
- ✓Sample type, subcellular location, expected abundance and relevant treatment time point.
- ✓Whether reducing and heating conditions are compatible with the target epitope.
- ✓Positive biological control, negative control and a loading/normalization strategy.
- ✓Antibody supplier’s validated sample, dilution buffer, dilution and expected band pattern.
- ✓Detection method and how you will preserve an unsaturated image for quantification.
Bench workflow
1. Collect and lyse the sample
Starting point
Work cold and quickly when degradation or labile modifications matter. Use a lysis method that recovers the compartment containing the target, and add the inhibitors required by the validated workflow.
Check
Check whether lysis is complete, whether the sample is excessively viscous, and whether the target may remain in the insoluble fraction. Measure protein with an assay compatible with the lysis matrix.
When to adjust
Change lysis chemistry or use fractionation when the target is membrane-associated, nuclear, insoluble or poorly recovered. Increasing sample load does not correct poor extraction.
2. Prepare samples for electrophoresis
Starting point
Normalize the intended protein input, keep lane chemistry comparable, add the appropriate sample buffer and reducing agent, then heat under conditions compatible with the target and gel system.
Check
Record protein mass and liquid volume per lane. Note precipitate or major differences in salt/detergent load between samples.
When to adjust
Use a loading series when the usable lane input is unknown. Some targets aggregate after harsh heating; compare an alternative heating condition only when there is a reason to suspect that problem.
3. Separate proteins by SDS-PAGE
Starting point
Choose the gel chemistry and percentage or gradient from the expected molecular-weight range and the separation task. Load an amount that preserves lane quality, plus a molecular-weight marker.
Check
Watch the dye front, ladder and lane shape. A clean ladder with distorted sample lanes points toward sample or loading chemistry; distortion across the whole gel points toward gel, buffer or run conditions.
When to adjust
Use the separation range documented for the exact gel system. Correct smiling, distorted lanes or broad smears before moving to transfer or antibody optimization.
4. Transfer proteins to membrane
Starting point
Assemble gel and membrane without bubbles. Equilibrate nitrocellulose directly in transfer buffer; pre-wet PVDF according to the membrane manufacturer. Follow the transfer-device instructions first.
Check
Inspect the membrane with Ponceau S or another reversible total-protein stain. Check the post-transfer gel when incomplete transfer is suspected.
When to adjust
Large proteins often need longer or cooler transfer and sometimes lower methanol; small proteins may need a shorter transfer and a 0.2 µm membrane to reduce blow-through. Use the transfer stain and, when needed, the post-transfer gel to guide adjustments.
Related guides
5. Block and choose antibody diluent
Starting point
Milk or BSA in TBST can both be useful starting systems, but use the product-specific blocker or primary-antibody diluent when the antibody protocol provides one.
Check
Record membrane blocker and primary-antibody diluent separately. For phospho targets, use the condition recommended for the specific antibody rather than assuming milk or BSA is always preferred.
When to adjust
If signal or specificity is poor, return to the supplier-recommended diluent before changing antibody concentration. Avoid changing blocker, antibody dilution and wash conditions in the same comparison.
Related guides
6. Incubate with primary antibody
Starting point
Use the supplier-validated dilution and diluent. Incubation time and temperature should follow the antibody guidance where available.
Check
Ensure the membrane stays covered and does not dry. Keep a map of membrane orientation, cuts and target positions.
When to adjust
Titrate around the validated condition only after checking target expression, transfer and detection. More antibody can raise background without restoring a target that is absent from the sample.
Related guide
7. Wash and incubate with secondary antibody
Starting point
Wash with fresh buffer using adequate volume and agitation. Match the secondary antibody to the primary host species and detection system.
Check
Record wash buffer, duration and agitation. Confirm that the secondary and detection chemistry are compatible and that the secondary condition suits the substrate sensitivity.
When to adjust
With uniform dark background, check secondary concentration, exposure, contamination and washing before changing the primary antibody.
Related guide
8. Detect, image and quantify
Starting point
Use fresh substrate or the correct fluorescent settings. Capture enough exposures to identify detector saturation and preserve uncropped source data.
Check
Before calculating ratios, confirm that target and normalization signals are unsaturated and share a usable sample range; also confirm that the chosen normalizer is stable in the experiment.
When to adjust
If target or normalizer is outside the usable range, repeat with adjusted sample, antibody or acquisition conditions. Do not quantify saturated bands or try to restore them with image editing.
Related guide
Minimum control set
Positive biological control
Confirms that the sample–antibody–detection chain can produce the expected band.
Negative biological control
A knockout, knockdown or known-negative sample tests whether the band follows the target.
No-primary control
Tests secondary-antibody and substrate background; it does not establish primary-antibody specificity.
Loading/normalization control
Use a control shown to be stable in the experiment, or use total-protein normalization when appropriate.
Transfer check
Ponceau S or another total-protein image helps separate transfer failure from later antibody or detection problems.
Record these values for every blot
• Sample source, treatment time, lysis buffer and inhibitors
• Protein assay, concentration, amount per lane and heating condition
• Gel system, percentage, voltage and run time
• Membrane/pore size, transfer system, time and current or voltage
• Membrane blocker, primary diluent, antibody catalog/lot and dilution
• Wash buffer, number, duration and secondary condition
• Substrate or fluorescence channel, exposure and imager settings
• Uncropped blot, linearity/saturation checks and normalization rule
Primary sources used for this page
- Cell Signaling Technology — Western Blot Procedure
- Cell Signaling Technology — Western Blot Troubleshooting Guide
- Thermo Fisher Scientific — Overview of Western Blotting
- Thermo Fisher Scientific — Protocols and Recipes
