Silver enhancement solution

Silver-enhancing solution (II) 60 mL protective colloid (25% gum arabic or 50% PEG [20,000 mol wt] or PVP), 10 mL 2 M citric acid or sodium citrate, and 850 mg hydroquinone dissolved in 15 mL deionized glass-distilled water mix thoroughly adjust pH to 3.8 immediately before use, add 110 mg silver lactate dissolved in 15 mL deionized glass-distilled water (see Note 2). 

Prepare silver-enhancing solution immediately prior to use, and cover the sections with the solution (see Note 6). 

Rinse sections in high-quality distilled water to remove all traces of chloride ions and other impurities that might contaminate the silver-enhancing solution. Some commercial enhancement solutions are reported to be resistant to contamination, the user should evaluate this carefully, especially if high levels of nonspecific background are encountered... 

Problems with nonspecific background silver deposition. Background silver deposition may be owing to the use of poor-quality antibodies, incorrectly diluted antibodies, old silver-enhancing solutions, poor-quality distilled water, or incorrect silver-enhancement times The silver-enhancement procedure is tempera-... 

Problems with nonspecific background silver deposition background silver deposition may result from the use of poor-quality antibodies, incorrectly diluted antibodies, old silver-enhancing solutions, poor-quality distilled water, or incorrect silver enhancement times. The silver enhancement procedure is temperature dependent and where laboratory temperatures vary a lot, especially at different times of the year, it is useful to construct a standardized temperature-enhancement time graph and keep it readily available at the bench (Fig. 3). As an example, adequate silver enhancement may take only 5 min at 25°C whereas the same result may take up to 15 min to obtain at 15°C. Enhancement times may be controlled more precisely by storing the enhancer components in the refrigerator at... 

Fig. 15.2 Silver enhancement of small gold, (a) The 1° antibody binds the antigen and the 2° antibody is labeled with small gold, (b) The silver enhancement solution was applied containing ionic sUver and a chemical developer, (c) The reaction deposited metallic silver on the gold particle.

The silver enhancement solution with its components mixed together will react in a few seconds and turn the solution black or brown. Gum arable is added to slow the rate of silver enhancement and MES buffer is added to control the pH. It is very important to mix the silverenhancement solution with the reagents in the proper order and exactly as described. The silver enhancement solution described here is sensitive to light, as are most of the commercial solutions, and needs to be mixed and used in a darkroom. Fortunately, the wavelength emitted by a sodium vapor safelight does not affect the solution, but is adequate to perform these procedures. 

Incubate test strip in the NPG silver enhancement solution under a sodium vapor safe light until labeling of test strip is similar to that determined previously as acceptable. Note the time required. 

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