Lab & analytical techniques · Reference
What is a Western blot?
A Western blot is a research method that detects a specific protein in a sample by separating proteins by electrophoresis, transferring them to a membrane, and probing with antibodies that bind the target.
The three steps
A Western blot combines three techniques. First, proteins are separated by gel electrophoresis, typically SDS-PAGE, which sorts them by size. Second, the separated proteins are transferred from the gel onto a membrane (often nitrocellulose or PVDF), preserving their pattern. Third, the membrane is probed with a primary antibody that binds only the target protein, followed by a labelled secondary antibody that recognises the first. The label — often an enzyme producing light, or a fluorophore — generates a band wherever the target sits, identified by its position relative to size markers.
Why antibodies make it specific
The specificity of a Western blot comes from the antibodies. Because an antibody binds a particular protein region (epitope), it can pick out one protein even from a complex mixture of thousands.
The size information from electrophoresis adds a second check: a genuine signal appears at the expected molecular weight. Controls and well-validated antibodies are essential, because a non-specific antibody can give misleading bands.
Uses in research
Western blotting is a standard tool in cell and molecular biology for confirming whether a protein is expressed, comparing its abundance between samples, and checking its approximate size or modification state. It complements antibody methods such as the ELISA. Reproducible blots depend on documented antibodies, validated controls, and reported imaging conditions — increasingly required so that protein data can be trusted and reused.
Key facts
At a glance
- Detects: a specific protein in a mixture
- Step 1: separation by gel electrophoresis (often SDS-PAGE)
- Step 2: transfer to a membrane (nitrocellulose or PVDF)
- Step 3: probing with primary and labelled secondary antibodies
- Specificity from: antibody–epitope binding
- Readout: a band at the protein's expected size
Common questions
FAQ
What is a Western blot used for?+
A Western blot is used in research to confirm that a specific protein is present in a sample, estimate its size, and compare its abundance between conditions. It is a standard method in cell and molecular biology.
How does a Western blot work?+
Proteins are separated by gel electrophoresis, transferred to a membrane, and probed with an antibody that binds the target protein. A labelled secondary antibody then produces a visible band wherever the target is located.
The step most authors miss
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