Silver diamine stain

The search for more rapid and sensitive methods of protein detection after electrophoresis led to the development of fluorescent staining techniques. Two commonly used fluorescent reagents are fluorescamine and anilinonaphthalene sulfonate. New dyes based on silver salts (silver diamine or silver-tungstosilicic acid complex) have been developed for protein staining. They are 10 to 100 times more sensitive than Coomassie Blue (Fig. 4.7). 

Diamine Stains Formation of silver diamine complexes, with ammonium hydroxide, offers a means of stabilizing silver ions in an alkaline environment. Diamine silver stains were first developed for the... 

In the diamine stains, the ammoniacal silver solution must be acidified, usually with citric acid, for image production to occur. The addition of citric acid lowers the concentration of free ammonium ions, thereby liberating silver ions to a level where their reduction by formaldehyde to metallic silver is possible. The optimal concentration of citric acid also results in a controlled rate of silver ion reduction, preventing a non-selactive deposition of si 1ver. 

The first photographic reducer used to destain silver-stained polyacrylamide gels employed ammonium hydroxide, copper sulfate and sodium thiosulfate (1 ). It is also a subproportional reducer. The diamine stains are most resistant, while the photodevelopment stains are most sensitive to destaining. 

Non-Diamine Chemical Development Stains Host of the non-diamine chemical development silver stains were developed by adapting photographic photochemical protocols (22-26). These stains rely on the reaction of silver nitrate with protein sites in acidic conditions, followed by the selective reduction of ionic silver by formaldehyde in alkaline conditions. Sodium carbonate and/or hydroxide and other bases are used to maintain an alkaline pH during development. Formic acid, produced by the oxidation of formaldehyde, is buffered by the sodium carbonate (27). 

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