A new chromogen for use in HRP-tract tracing and double-label immunocytochemistry

A new chromogen, Indophane Blue (IB) was tested for use in HRP-tract tracing and double-label immunocytochemistry. Although TMB was slightly more sensitive and delineated individual labeled fibers better than IB in tract-tracing experiments, there were two advantages to using IB over TMB. First, the IB reaction could be performed at a pH of 6.0, rather than the pH of 3.3 required for TMB, resulting in much better preservation of tissue. Second, there was no crystalline artifact as has been observed with TMB. In the double-label immunocytochemistry experiments, the combination of diaminobenzidine for the first chromogen and IB as the second, provided excellent contrast.