Silver stain

The silver staining is a procedure for staining proteins, DNA and RNA in polyacrylamide gels after electrophoresis, or thin sections of tissue.

History

The method is based on the development of photographs. This developed in the 19th century from the photograms Thomas Wedgwood, followed by the Daguerreotype and the Calotype. Camillo Golgi in 1873 used the silver staining under the name " la reazione nera " (in German, the black reaction ') for contrasting the nervous system in tissue sections, and later became known as the Golgi method.

Applications

Molecules in biological tissue, which enhances binding of silver ions are referred to as argyrophil. There are also argentaffine molecules that bind silver ions and can also reduce.

Histology

Today, the silver staining of tissues issue also includes the methenamine silver staining according to Grocott -based (at different fungi ), according to Gomori or after Jones ( stained basement membranes in the diagnosis of glomerulonephritis ) were used.

In a von Kossa staining, the silver ions are precipitated by phosphates. By subsequent reduction with hydroquinone produced black-brown, elemental silver. Thus, the formation of hydroxyapatite can be stained eg in osteoblasts.

Biochemistry

Silver staining of proteins in agarose gels has been developed in 1973 by Kerenyi and Gallyas and since optimized for polyacrylamide gels and also for DNA or RNA. The glycosylation of glycoproteins and polysaccharides can be oxidized by one-hour pre-treatment with a 0.1% solution of periodic acid at 4 ° C so that the deposition of silver ions can be improved.

First, the proteins are denatured by a fixing solution consisting of 10% glacial acetic acid and 30% ethanol in the gel and precipitate, at the same time the detergent is (typically SDS ) is removed. The diffusion of proteins is significantly reduced. After repeated washing with water, the gel is incubated in a solution of silver nitrate. Here, silver ions adsorb on the negatively charged side chains of proteins. Excess silver is then washed off with water. In the final stage of development, the silver ions are reduced by the addition of alkaline formaldehyde to elemental silver. This colors the points at which proteins are present, black.

The intensity of the color depends on the primary structure of the protein. Furthermore, the cleanliness of the vessel being used and the purity of the reagents, affects the silver staining.

This method is characterized by its high sensitivity in comparison to Coomassie stained gels. The detection limit is 0.1 ng to 1 ng per band.

Argyria

Argyria is a condition which can be caused by regular intake of silver salts or silver colloids and can manifest itself in a gray coloring of the skin, night blindness and kidney failure.