A differentiated silver intensification procedure for the peroxidase-diaminobenzidine reaction

Several silver-based procedures have been developed to intensify the peroxidase-catalyzed diaminobenzidine polymer used as a marker in immunohistochemistry. Many of these methods use acutely unstable reagents or reagents that are not amenable to batch processing. We describe a new procedure with an initial treatment in dilute ammoniacal silver, followed by a differentiation step to remove background staining and a final toning in 0.2% gold chloride. The procedure provides a jet-black intensification of the tan diaminobenzidine product, is amenable to batch processing of free-floating sections and slide-mounted sections, and does not require acid-cleaned glassware.