Utilizing the same chemistry as black and white photography, silver staining is another highly sensitive method for the visualization of protein bands on electrophoresis gels. Silver ions are reduced to insoluble silver metal granules in the vicinity of the protein molecules. Sufficient silver deposition is visible as a dark brown or black band on the gel.

The exact mechanism of silver staining is subject to debate, but certain key points are generally acknowledged. Staining appears to be dependent upon the initial reduction and resulting immobilization of a small number of silver ions by the proteins in the gel. This reduction may be caused by aldehydes created during fixing with glutaraldehyde or with oxidizing agents (e.g. chromic acid). Reduction of silver may also be enhanced by sequestration of the silver cations by carboxylic acid side chains, or by amino side chains, creating an amine-silver complex.

The initial deposition of silver is referred to as a latent image. This "image" is not visible, as the number and size of the silver granules deposited at this stage are minute. In the next stage a moderate reducing environment is created in the gel, in which all of the silver ions begin to “plate out” slowly. The silver granules which make up the latent image act to catalyze this process, resulting in more rapid deposition of silver at the sites of the protein bands. Silver staining is thus a kinetic process: development must be monitored and stopped at the point where the highest contrast between band and background is achieved.

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