Why did my Western blot fail?

Playbooks

• Western blot: no bandsNo specific immunoreactive bands on the blot, including expected positive targets.
• Western blot: high backgroundElevated membrane background obscuring specific bands.
• Western blot: uneven transferPatchy or gradient protein transfer across lanes or the membrane.
• Western blot: unexpected sizeSpecific band(s) appear at a molecular weight different from the expected size.
• Western blot: multiple bandsMore immunoreactive bands than expected for the target.
• Western blot: faint bandsSpecific bands present but weaker than expected for the load and antibody.

Calculators

• Molarity converterConvert between nM, µM, mM, and M.
• Dilution (C1V1)Solve C1V1 = C2V2 and plan serial dilutions.
• Buffer recipesStandard bench buffers with per-liter amounts.

FAQ — Western blot

No bands

No specific immunoreactive bands on the blot, including expected positive targets. Confirm transfer with Ponceau/ladder on the membrane before blotting — Separates transfer failure from antibody/detection failure in one glance. Re-probe with a fresh primary aliquot at a validated dilution (e.g. 1:1000) — Rules out inactive or mis-stored primary antibody. Switch blocker to 5% BSA if the target is phospho-sensitive to milk casein — Milk can mask phospho-epitopes; BSA is the usual alternative. Increase imager exposure stepwise (30 s → 2–5 min) on a positive-control lane — Under-exposure is a common silent failure after a camera preset change.

High background

Elevated membrane background obscuring specific bands. Add 2 extra TBST + 0.1% Tween washes (5 min each) after secondary — Highest-yield fix for uniform membrane background. Re-block 1 h at RT with fresh 5% milk or BSA in TBST — Expired or weak blocker is the second most common cause. Titrate secondary (and if needed primary) 2-fold downward — Cuts nonspecific binding while retaining true signal. Shorten exposure until background is below the specific band — Separates chemistry background from camera saturation.

Uneven transfer

Patchy or gradient protein transfer across lanes or the membrane. Re-assemble the sandwich under transfer buffer; roll out bubbles firmly — Bubbles are the most common local void pattern. Make fresh transfer buffer; verify pH 8.3 and methanol % for PVDF vs nitrocellulose — Wrong buffer composition causes edge/centre gradients. Extend wet transfer (e.g. 30 V / 90 min → 100 min) for targets >100 kDa — Large proteins often need more time; confirm with Ponceau + residual gel stain.

Unexpected size

Specific band(s) appear at a molecular weight different from the expected size. Re-denature samples with fresh reducing agent; heat 95 °C / 5 min — Incomplete reduction is the most actionable size artefact. Confirm ladder lot and gel %, then re-estimate MW — Rules out scale mis-assignment before biological interpretation. Test a second primary clone or peptide-block the antibody — Separates true isoform/PTM from off-target binding.

Multiple bands

More immunoreactive bands than expected for the target. Titrate primary 2-fold down and compare specific vs extra bands — Non-specific bands usually drop faster than the true target. Lyse on ice with fresh protease (and phosphatase) inhibitors — Stops degradation ladders that look like multiple specific bands. Include a no-primary control strip to check secondary background — Identifies Ig/Fc artefacts before changing primary clones.

Faint bands

Specific bands present but weaker than expected for the load and antibody. Increase protein load (e.g. toward 30 µg/lane) and re-check loading control — Confirms whether the issue is amount versus detection chemistry. Use a fresher primary aliquot or increase antibody concentration one step — Partial degradation presents as uniformly faint specific bands. Extend transfer or raise voltage within membrane limits; confirm with Ponceau — Incomplete transfer selectively weakens some MW ranges. Lengthen exposure or replace ECL substrate — Under-detection is quick to rule in/out.