Western blot (WB) is one of the most fundamental techniques in molecular biology, used to detect and quantify specific proteins in complex biological samples. This step-by-step guide covers the complete workflow — from sample preparation through detection — with practical tips at each stage. For troubleshooting common WB problems, see our WB Troubleshooting Guide.
Workflow Overview
1. Sample Preparation & Protein Extraction
2. Protein Quantification
3. SDS-PAGE Gel Electrophoresis
4. Protein Transfer to Membrane
5. Blocking
6. Primary Antibody Incubation
7. Secondary Antibody Incubation
8. Detection & Imaging
1. Sample Preparation & Protein Extraction
The quality of your WB result starts with sample preparation. The goal is to extract intact, soluble protein from your cells or tissue while minimizing degradation. For detailed lysis buffer selection guidance, see our Cell Lysis & Protein Extraction Guide.
| Sample Type |
Lysis Buffer |
Protocol Notes |
| Adherent cells |
RIPA buffer |
Wash with cold PBS, add lysis buffer directly to plate, scrape and collect. Add protease inhibitors fresh. |
| Suspension cells |
RIPA buffer |
Pellet cells (300 × g, 5 min), wash with cold PBS, resuspend in lysis buffer. |
| Tissue |
RIPA + mechanical disruption |
Homogenize in cold RIPA using Dounce homogenizer or bead beater. Keep on ice throughout. |
Critical: Add protease inhibitors (PMSF, aprotinin, leupeptin, or a commercial cocktail) to lysis buffer immediately before use. For phosphoprotein detection, also add phosphatase inhibitors (NaF + Na₃VO₄). See our phospho antibody guide for details.
2. Protein Quantification
Equal protein loading across lanes is essential for valid comparisons. Measure total protein concentration using BCA or Bradford assay, then normalize all samples to the same concentration (typically 1–4 μg/μL) before adding sample buffer.
| Assay |
Compatible With |
Not Compatible With |
| BCA |
Most detergents (SDS, Triton, NP-40) |
Reducing agents (DTT >1 mM, β-ME) — interfere with Cu²⁺ reduction |
| Bradford |
Most reducing agents |
SDS >0.1% — disrupts dye binding |
Typical loading: 20–50 μg total protein per lane for most targets. For highly abundant proteins (β-actin, GAPDH), 10–20 μg is sufficient. For low-abundance targets, load up to 80–100 μg.
3. SDS-PAGE Gel Electrophoresis
Add 4× Laemmli sample buffer (with β-mercaptoethanol or DTT) to your protein samples. Boil at 95°C for 5 minutes to denature proteins. Load samples into wells alongside a pre-stained molecular weight marker.
| Target MW |
Gel Percentage |
Resolution Range |
| <15 kDa |
15–20% or Tricine gel |
Best for small proteins and peptides |
| 15–50 kDa |
12% |
Standard for most targets |
| 50–100 kDa |
10% |
Good balance for mid-range proteins |
| 100–200 kDa |
8% |
Large proteins |
| Wide range |
4–20% gradient |
Separates 10–250 kDa on one gel |
Run conditions: 80 V through stacking gel, then 120–150 V through resolving gel. Run until the dye front reaches the bottom of the gel (typically 60–90 min).
4. Protein Transfer to Membrane
Transfer proteins from the gel to a PVDF or nitrocellulose membrane. The choice of membrane and transfer method depends on your target and detection system.
| Membrane |
Advantages |
Best For |
| PVDF |
Higher protein binding capacity; more durable; can be stripped and reprobed |
Most WB applications; low-abundance targets |
| Nitrocellulose |
Lower background; no methanol activation needed |
Fluorescent detection; near-infrared imaging |
Tip: After transfer, stain the membrane with Ponceau S (0.1% in 5% acetic acid, 5 min) to verify even transfer across all lanes. This is reversible — wash with TBST before blocking. For loading control guidance, see our dedicated guide.
Wet transfer: 100 V for 60–90 min (or 30 V overnight) in transfer buffer (25 mM Tris, 192 mM glycine, 20% methanol). Keep the tank cold with an ice pack or run in cold room.
Semi-dry transfer: 25 V for 30–60 min. Faster but may be less efficient for large proteins (>100 kDa). For proteins >100 kDa, wet transfer with 0.01–0.05% SDS in transfer buffer and extended time is recommended.
5. Blocking
Blocking prevents non-specific antibody binding to the membrane. The choice of blocking reagent matters:
| Blocking Reagent |
Use When |
Avoid When |
| 5% non-fat milk / TBST |
Standard WB for non-phospho targets |
Phospho-specific antibodies (casein is phosphorylated); biotin-streptavidin detection (milk contains biotin) |
| 5% BSA / TBST |
Phospho-protein detection; biotin-streptavidin systems |
Generally safe for all applications; slightly higher cost than milk |
Protocol: Block for 1 h at room temperature with gentle agitation. Do not over-block (>2 h) as this can reduce signal by masking the antigen.
6. Primary Antibody Incubation
Dilute the primary antibody in blocking buffer (or 5% BSA/TBST) at the concentration recommended on the product datasheet. For monoclonal vs polyclonal antibody selection guidance, see our dedicated guide.
Standard incubation: Overnight at 4°C with gentle rocking. This provides the best signal-to-noise ratio for most antibodies.
Quick incubation: 1–2 h at room temperature. Faster but may produce higher background.
Wash: 3 × 10 min with TBST after primary antibody incubation.
7. Secondary Antibody Incubation
The secondary antibody must match the host species and isotype of the primary antibody. For HRP-conjugated secondaries, typical dilutions are 1:2,000–1:10,000.
| Primary Host |
Secondary Needed |
abinScience Product |
| Rabbit |
Goat Anti-Rabbit IgG (HRP) |
Cat# TF690314 |
| Mouse |
Goat Anti-Mouse IgG (HRP) |
Cat# MF690314 |
Protocol: Incubate 1 h at room temperature with gentle rocking.
Wash: 3 × 10 min with TBST. Thorough washing here is critical for low background.
WB Essentials from abinScience
Goat Anti-Rabbit IgG H&L (HRP) — Cat# TF690314 | WB 1:5,000–1:10,000
Goat Anti-Mouse IgG H&L (HRP) — Cat# MF690314 | WB 1:5,000–1:10,000
Anti-β-Actin Recombinant (SAA0339) — Cat# HX034013 | Loading control, 42 kDa
Anti-Human GAPDH Monoclonal (1A200) — Cat# HY030035 | Loading control, 36 kDa
Browse All WB-Validated Antibodies →
8. Detection & Imaging
For HRP-conjugated secondaries, add ECL (Enhanced Chemiluminescence) substrate and image immediately. The signal typically peaks within 1–5 minutes and gradually fades.
Film exposure: Start with 30 s, then adjust. Multiple exposures (10 s, 30 s, 1 min, 5 min) ensure you capture optimal signal without saturation.
Digital imaging: CCD-based systems (ChemiDoc, iBright, Amersham) provide linear dynamic range and quantitative data. Use auto-exposure first, then optimize.
Quantification: Use densitometry software (ImageJ, Image Lab) to measure band intensity. Always normalize target band intensity to your loading control (β-actin, GAPDH, or total protein stain).
Troubleshooting version: WB Troubleshooting Guide on protocols.io →
References
1. Mahmood T, Yang PC. Western blot: technique, theory, and trouble shooting. N Am J Med Sci. 2012;4(9):429-434. doi: 10.4103/1947-2714.100998
2. Bass JJ, et al. An overview of technical considerations for Western blotting applications to physiological research. Scand J Med Sci Sports. 2017;27(1):4-25. doi: 10.1111/sms.12702
3. Ghosh R, et al. The necessity of and strategies for improving confidence in the accuracy of western blots. Expert Rev Proteomics. 2014;11(5):549-560. doi: 10.1586/14789450.2014.939635
Primary + Secondary + Loading Control = Complete WB System
Every abinScience antibody datasheet includes recommended WB dilutions, validated applications, and expected band sizes.
Browse WB Antibodies →
This article is provided for educational purposes only. For technical support, contact [email protected].
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