blot

Blot may refer to a stain or mark left by a liquid, or to the act of absorbing a liquid with an absorbent material. In biology, blotting refers to a family of laboratory techniques used to transfer and detect biomolecules. The most well-known are the Southern blot (DNA), the Northern blot (RNA), and the Western blot (protein). These methods share a common workflow: samples are separated by gel electrophoresis, then transferred to a membrane such as nylon or nitrocellulose by capillary action or electrical current (electroblotting). The membrane is probed with labeled nucleic acids or antibodies to reveal specific sequences or proteins; detection methods include autoradiography, chemiluminescence, or fluorescence. Variants exist for other biomolecules, such as Far-Eastern blot for lipids and glycoproteins, and Southwestern blot for DNA-protein interactions.

Blotting has wide use in research to analyze gene expression, verify the presence of particular biomolecules, or characterize molecular size. In clinical contexts, blotting techniques underpin some diagnostic tests, and a Western blot is used as a confirmatory test for certain infections, such as HIV, after an initial screening. In everyday language, blot can also simply mean a conspicuous stain or a stain mark, often requiring blotting paper to remove it.

Related terms include blotting paper, a highly absorbent material used to lift liquids, and various blot-based tests in serology or pathology.