Small-protein transfer
Western blot transfer for small proteins: pore size, blow-through and retention
Use this page when a low-molecular-weight target is missing or inconsistent. Check gel resolution, membrane pore size, possible blow-through, post-transfer retention and antibody detection as separate causes.
Why this matters
A small target can be lost even when the rest of the membrane looks normal
Small proteins leave the gel quickly and can pass through a larger-pore membrane or be lost during later handling. Extending transfer can therefore make a weak low-MW result worse. Check where the protein went before changing transfer time.
Practical starting point
Use a gel system that resolves the target and a membrane pore size appropriate to the low-MW range. Start with the transfer-device program, then shorten or reduce transfer only when the membrane or catch-membrane result supports that change.
Use a small-pore membrane when the target is very small
Manufacturer guidance commonly recommends a 0.2 µm membrane for very low-molecular-weight proteins that may pass through a 0.45 µm membrane. Thermo Fisher specifically flags proteins below about 10 kDa as high risk for blow-through on 0.45 µm membrane.
Do not automatically extend transfer
If a small target is weak, first check whether it passed through. Shorter time or reduced field can improve retention when transfer is too aggressive.
Keep SDS conservative
SDS promotes elution but can reduce membrane binding. For a small target already prone to blow-through, avoid unnecessary SDS unless the gel or transfer-system protocol requires it.
Consider methanol as part of membrane retention
Methanol can support membrane binding by removing SDS, but the exact percentage remains system-specific. Adjust it only with device or membrane guidance and an observed retention problem.
Conditions that matter most for small-protein transfer
Membrane pore size
A 0.2 µm membrane reduces the chance that very small proteins migrate through larger pores and is often the first variable to review.
Transfer duration
Small proteins can transfer quickly. If a catch membrane confirms blow-through, shorten transfer before changing antibodies.
Voltage / current
A less aggressive transfer can improve retention, but the appropriate adjustment is system-specific. Compare conditions within the device’s validated range.
Methanol and SDS
Methanol supports membrane binding, while SDS supports protein elution but can reduce membrane binding. Change either only when the transfer result gives a reason to do so.
Post-transfer fixation
Some validated methods for very small proteins or peptides use post-transfer fixation or crosslinking to improve retention. Because fixation can affect epitopes, use it only when validated for the target and membrane.
Detection versus transfer loss
A missing low-MW antibody band does not prove blow-through. A second membrane, transfer stain and known-positive small target provide stronger information.
Check for small-protein blow-through before changing antibodies
Use pore size, transfer duration and a catch membrane or validated small-target control to distinguish blow-through from antibody or abundance problems.
What to record for a missing small target
Common results and next actions
Check separately whether the protein left the gel, stayed on the membrane and was detected by the antibody.
Observation
The target appears on a second membrane behind the first
Interpretation
Blow-through is directly supported.
Next action
Use a 0.2 µm membrane if appropriate, shorten transfer or reduce field within the device range, and remove unnecessary SDS.
Avoid
Do not extend transfer or increase antibody first.
Observation
Target is absent from the first and second membranes but remains in the gel
Interpretation
This indicates under-transfer or gel retention rather than blow-through.
Next action
Return to transfer optimization and gel selection; do not automatically shorten transfer.
Avoid
Do not let the target’s small size force the wrong adjustment.
Observation
Total-protein or marker evidence reaches the low-MW region, but the target antibody is absent in a known-positive sample
Interpretation
Transfer may be adequate; antibody epitope, abundance, sample handling or detection needs investigation.
Next action
Validate the antibody and expected apparent mass while keeping transfer fixed.
Avoid
Do not call it blow-through without a catch-membrane or retention clue.
Observation
The target is present immediately after transfer but weakens after processing
Interpretation
Post-transfer retention or washing conditions may be contributing.
Next action
Confirm membrane choice and handling; consider fixation only when it has been validated for the target and method.
Avoid
Do not introduce fixation blindly because it can alter antigenicity.
Related small-protein guides
Transfer optimization
Adjust field, time, methanol and SDS using membrane and catch-membrane results.
Open →
Transfer guide
Review membrane and transfer-format selection.
Open →
Small-protein loss case
Review the case and the checks needed to distinguish the possible causes.
Open →
Troubleshooting guide
If transfer is adequate, check antibody, sample and detection causes.
Open →
Primary sources used for this guide
The 0.2 µm recommendation and blow-through troubleshooting come from manufacturer guidance. Exact transfer programs remain device-specific.
- Thermo Fisher Scientific — Western Blotting Support: Troubleshooting
Low-MW blow-through, 0.2 µm membrane, reducing transfer intensity or time, SDS and methanol tradeoffs, and second-membrane checks.
- Bio-Rad — Separating Proteins to a Blotting Membrane
Small proteins can pass through the membrane; smaller pore sizes and catch membranes can help with retention and diagnosis.
- Bio-Rad — Introduction to Western Blotting
General Western blot workflow context.