Copper-H2O2 oxidation strikingly improves silver intensification of the nickel-diaminobenzidine (Ni-DAB) end-product of the peroxidase reaction.

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Abstract
We propose an improved silver procedure for intensification of peroxidase staining. It utilizes the high argyrophilia of polymerized Ni-DAB as a chromogen of peroxidase histochemistry, and the capacity of Cu++-catalyzed H2O2 oxidation to suppress tissue argyrophilia without influencing the argyrophilia of the polymerized Ni-DAB. This procedure is much more effective than any previously proposed intensification technique. When used in somatostatin histochemistry, it reveals perikarya, fibers, and nerve terminals in locations at which they have never been detected in preparations where only the DAB polymer was silver-intensified.