A highly sensitive one-step method for silver intensification of the nickel-diaminobenzidine endproduct of peroxidase reaction.

We have developed a new technique which makes silver intensification of the oxidatively polymerized diaminobenzidine (DAB), the endproduct of peroxidase reaction, less laborious without any loss in selectivity or sensitivity. The new technique is based on two strategies: (a) increasing the argyrophilia of the DAB by modifying its polymerization with Ni ions, and (b) decreasing tissue argyrophila by using a mildly acidic physical developer instead of the alkaline one previously presented. Because the nickel modification takes place in the DAB substrate solution, i.e., in the final step of the peroxidase reaction, only one additional step, the physical development, must be carried out if intensification is needed.