In molecular biology and genetics, a blot is a method of transferring proteins, DNA or RNA, onto a carrier (for example, a nitrocellulose PVDF or nylon membrane). In many instances, this is done after a gel electrophoresis, transferring the molecules from the gel onto the blotting membrane, and other times adding the samples directly onto the membrane. After the blotting, the transferred proteins, DNA or RNA are then visualized by one or more different methods:

• colorant staining (for example, silver staining of proteins)
• autoradiographic visualization of radioactive labelled molecules (performed before the blot)
• specific labelling of some proteins or nucleic acids. It is done with antibodies or hybridization probes that bind only to some molecules of the blot and have an enzyme joined to them. After proper washing, this enzymatic activity (and so, the molecules we search in the blot) is visualized by incubation with proper reactive, rendering either a colored deposit on the blot or a chemiluminiscent reaction which is registered by photographic film.

Common blot methods are :

• Southern blot for DNA
• Northern blot for RNA
• Western blot for proteins
• Southwestern blot
• Dot blot
• Slot blot