Silver stain

Silver staining is the use of silver to selectively alter the appearance of a target in microscopy of histological sections; in temperature gradient gel electrophoresis; and in polyacrylamide gels.

History

Camillo Golgi perfected silver staining for the study of the nervous system. Although the exact chemical mechanism by which this occurs is unknown, Golgi's method stains a limited number of cells at random in their entirety.

Silver staining was introduced by Kerenyi and Gallyas as a sensitive procedure to detect trace amounts of proteins in gels. The technique has been extended to the study of other biological macromolecules that have been separated in a variety of supports.

Classical Coomassie Brilliant Blue staining can usually detect a 50 ng protein band; silver staining increases the sensitivity typically 50 times.

Many variables can influence the colour intensity and every protein has its own staining characteristics; clean glassware, pure reagents and water of highest purity are the key points to successful staining.

Chemistry

Some cells are argentaffin. These reduce silver solution to metallic silver after formalin fixation. Other cells are argyrophilic. These reduce silver solution to metallic silver after being exposed to the stain that contains a reductant, for example hydroquinone or formalin.

Silver nitrate forms insoluble silver phosphate with phosphate ions; this method is known as the Von Kossa Stain. When subjected to a reducing agent, usually hydroquinone, it forms black elementary silver. This is used for study of formation of calcium phosphate particles during bone growth.

Applications

Histological characterisation

Silver staining aids the visualization of targets of interest, namely intracellular and extracellular cellular components such as DNA and proteins, such as type III collagen and reticulin fibres by the deposition of metallic silver particles on the targets of interest.

Diagnostic microbiology

Pseudomonas, Legionella, Leptospira, H. pylori, and fungi such as Pneumocystis and Candida are organisms that are stained with silver.

Karyotype analysis

Silver staining is used in karyotyping. Silver nitrate stains the nucleolar organization region (NOR)-associated protein, producing a dark region wherein the silver is deposited and denoting the activity of rRNA genes within the NOR. Human chromosomes 13, 14, 15, 21, and 22 have NORs, which increase the silver stain activity by at least 50 times.

Genomic and proteomic analysis

Silver staining is used to stain gels

In art

Silver staining is also a technique in traditional stained glass to produce the yellow, brown, or amber shading when painting on glass. It is a technique that is often used for realistic hair colors. It was discovered in the 14th Century but was not originally used very frequently.

Variations

Methenamine silver stains

There are several silver stains incorporating methenamine, including:

• Grocott's methenamine silver stain, used widely as a screen for fungal organisms.
• Jones' stain, a methenamine silver-Periodic acid-Schiff that stains for basement membrane, availing to view the "spiked" GBM associated with membranous glomerulonephritis.

Gallery

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  A silver stain (GMS) demonstrating the fungus Histoplasma (black round balls) in a liver biopsy.

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  A number of DNA samples from specimens of Littorina plena amplified using PCR with primers targeting a variable simple sequence repeat (SSR, a.k.a. microsatellite) locus. Samples have been run on a 5% polyacrylamide gel and visualized using silver staining.

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  RBC membrane proteins separated by SDS-PAGE and silver-stained.

External links

• MedEd at Loyola Histo/practical/stains/hp2-55.html
• [1] Hempelmann E. SDS-Protein PAGE and protein detection by silverstaining and immunoblotting of Plasmodium falciparum proteins. in: Moll K, Ljungström J, Perlmann H, Scherf A, Wahlgren M (eds) Methods in Malaria Research, 5th edition, 2008, 263-266