1. After DAB chromogenic reaction, wash the tissue section 3 times with distilled water, 5 min each.
2. Add this reagent to the tissue section to cover the sample, after 30-60 seconds, wash the section with distilled water to remove the haematoxylin.
3. Immerse the section into saturated Na2HPO4 for 2 minutes, when the color changes into blue, wash the section, seal and observe under microscope.