What are the signal amplification methods used in immunohistochemistry (IHC)?

The three main signal amplification methods used in immunohistochemistry (IHC) include: 

1. Avidin-Biotin Complex (ABC) Method: This method forms the avidin-biotin-enzyme complex. It offers greater sensitivity compared to direct conjugation of enzymes to the secondary antibody because of the high enzyme-to-antibody ratio. 
2. Labeled Streptavidin-Biotin (LSAB) Method: This method forms the Streptavidin-enzyme complex. It offers enhanced sensitivity and enhanced tissue penetration compared to the ABC method because of its smaller complex size. 
3. Polymer-Based Method: This method forms the polymer backbone-enzyme complex. It offers greater sensitivity and specificity than the ABC and LSAB methods because of the larger number of antibodies and enzymes conjugated to the polymer. This method incorporates staining in a single step, resulting in fewer procedural steps compared to ABC and LSAB.