In molecular biology and genetics, a blot is a method of transferring large biomolecules (proteins, DNA or RNA) onto a carrier, such as a membrane composed of nitrocellulose, polyvinylidene fluoride or nylon. 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 molecules are then visualized by colorant staining (for example, silver staining of proteins), autoradiographic visualization of radiolabelled molecules (performed before the blot), or specific labelling of some proteins or nucleic acids. The latter 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 found in the blot) is visualized by incubation with a proper reagent, rendering either a colored deposit on the blot or a chemiluminescent reaction which is registered by photographic film.