Dot Blot Protocols

A dot blot, or slot blot, is a technique molecular biologists use to detect biomolecules by applying a mixture containing the biomolecules directly on a membrane as a dot. Nucleotide probes or antibodies then detect the biomolecules. This method provides confirmation of the presence or absence of specific biomolecules and does not provide information about the biomolecule's size, so other tests are required.

Southern Blot

• Southern blotting is a protocol that detects a specific DNA sequence. It combines the transfer of DNA fragments that have been chemically separated to a filter membrane with the detection of fragments found through probe hybridization. Southern blots determine the number of sequences, or gene copies, in a genome. This process is named for British biologist Edwin Southern, who developed it in 1975.

Northern Blot

• Northern blotting studies gene expression by detecting the RNA in a sample. This protocol makes it possible to observe a cell's control over its structure and function. Northern blotting determines particular gene expressions during a cell's stages of development as well as in abnormal or diseased conditions.

  Northern blotting, which separates RNA samples by size, detects part of the entire target sequence. A team of scientists at Stanford University developed the method n 1977.

Western Blot

• The Western blot, also called protein immunoblot, detects specific proteins in a tissue sample. It uses gel electrophoresis, which separates native or denatured proteins by its polypeptide length or by the protein's structure. After biologists transfer the proteins to a membrane, they use antibodies specific to the target protein to detect them.

  Western blotting is used to diagnose HIV, mad cow disease, some forms of Lyme disease, hepatitis B and feline AIDS.

Southwestern Blotting

• Southwestern blotting involves identifying and characterizing DNA-binding proteins though their ability to bind to specific probes. This process -- done via gel electrophoresis and then transferred to specific cell membranes -- combines the protocols of Southern blotting and Western blotting.