Causes & fixes:
| Cause | Solution |
|---|---|
| Too much protein loaded | Reduce loading amount (try 20–30 µg lysate) |
| Sample not fully denatured | Boil samples longer (5–10 min at 95°C) with fresh β-mercaptoethanol |
| Dirty or degraded gel | Use fresh gel or store properly at 4°C |
| Running buffer too old | Make fresh 1X running buffer |
| Gel overheated | Run at lower voltage (80–120V instead of 150–200V) |
Quick fix: Load less protein and run at 100V constant.
Causes:
Air bubbles trapped during pouring (hand-cast gels)
Bubbles in the sample when loading
Too much APS/TEMED causing rapid polymerization
Fixes:
Pour stacking gel slowly and insert comb at an angle
Centrifuge samples briefly before loading
Use degassed buffers
Pro tip: If using hand-cast gels, overlay resolving gel with water or isopropanol slowly—dripping from a pipette introduces bubbles.
Smiling (bands curve up at edges): Gel overheated or running voltage too high → reduce voltage and use cold running buffer.
Frowning (bands curve down at edges): Usually indicates a pH or salt issue in the gel or buffer.
Quick fix: Pre-run the gel at 50V for 10 minutes before loading samples.
Causes:
Uneven gel thickness
Comb inserted crooked
Air bubbles under the gel
Casting frame not level
Fixes: Check that the casting stand is level. Ensure plates are clean and evenly clamped. Insert comb straight, not tilted.
| Problem | Solution |
|---|---|
| Wrong gel percentage | Use lower % for large proteins (>100 kDa), higher % for small (<25 kDa) |
| Gel ran too short | Run until the dye front reaches the bottom |
| Voltage too low | Increase to 120–150V for faster separation |
Cheat sheet:
8% gel → 50–200 kDa
10% gel → 20–150 kDa
12% gel → 15–80 kDa
15% gel → 10–50 kDa
Glycerol missing from loading buffer → add glycerol or 2X loading buffer
Well not rinsed after removing comb → rinse wells with running buffer using a syringe
Air bubble trapped under sample → use a gel-loading tip and expel slowly
Short answer: Yes, but with caution.
For standard gels: Reuse 1–2 times max.
For Western blots (transfer): Always use fresh buffer.
Signs buffer is spent: pH changes, foaming, slower runs, smeary bands.
This is the most dreaded result. Work through this checklist:
| Check | What to do |
|---|---|
| Primary antibody works? | Run a positive control lysate |
| Secondary antibody works? | Dot blot or test on a known sample |
| Transfer worked? | Stain membrane with Ponceau S after transfer |
| Blocking overdone? | Don’t block longer than 1 hour at RT |
| Antibody concentration too low? | Titrate antibodies (try 1:1000 first) |
| Protein loaded? | Check gel with Coomassie stain |
Most common cause: Transfer failure or wrong antibody.
| Cause | Fix |
|---|---|
| Blocking insufficient | Use 5% milk or BSA for 1 hour at RT |
| Antibody concentration too high | Dilute further (e.g., 1:5000 instead of 1:1000) |
| Wash steps too short | Wash 3×10 minutes with TBST |
| Membrane dried out during incubation | Keep membrane wet at all times |
| Old or aggregated secondary antibody | Centrifuge secondary before use |
Normal vs problematic:
Normal: Some proteins have isoforms, post-translational modifications, or degradation products.
Problematic: Too many unexpected bands.
Fixes:
Use a more specific primary antibody
Add protease inhibitors to lysates
Reduce exposure time during detection
Run a negative control (knockdown or no-primary control)
Check these:
Transfer time too short → 1 hour at 100V (wet transfer) or 7–10 minutes (semi-dry)
Methanol concentration wrong → 20% for proteins >80 kDa, less for small proteins
Air bubbles between gel and membrane → Roll out bubbles with a serological pipette
Wrong membrane → PVDF for proteins <20 kDa, nitrocellulose for most others
Ponceau S staining is your best friend—it immediately shows if transfer worked.
Cause: Air bubbles trapped between the gel and membrane during transfer. These block protein transfer locally.
Fix: After assembling the transfer sandwich, roll firmly with a 10 mL pipette or a roller. Use transfer buffer to keep everything wet.
Yes, absolutely. Use stripping buffer (e.g., Restore PLUS or homemade: 62.5 mM Tris pH 6.8, 2% SDS, 100 mM β-mercaptoethanol) at 50°C for 30 minutes.
Check stripping success: Re-incubate with secondary antibody only—no signal means stripping worked.
Limits: Membranes can be stripped 2–3 times before signal loss.
| Method | Best for | Time | Efficiency |
|---|---|---|---|
| Wet transfer | Large proteins (>150 kDa), high resolution | 1–2 hours | High |
| Semi-dry | Routine proteins (20–150 kDa) | 10–30 min | Medium |
| Rapid (Turbo/TurboBlot) | Quick screening | 3–10 min | Medium |
Tip: For very large proteins, use wet transfer with low voltage overnight at 4°C.
This means transfer worked, but your antibody didn’t.
Solutions:
Increase primary antibody concentration or incubation time (overnight at 4°C is best)
Use a different blocking buffer (some antibodies don’t like milk—try BSA)
Check that your target protein is expressed in your sample
Run a positive control lysate
Western blotting is powerful but finicky. The difference between a perfect blot and a disaster is often one small variable—blocking time, methanol percentage, or a bubble you didn’t see.
The good news: almost every problem has been solved before. Use this guide as your first stop when something goes wrong.
Still stuck? Check the comments below—choose your pre-cast gel!https://ahelixbiotech.com/collections/precast-gel
