Chromogenic detection is a technique used in immunohistochemistry to visualize the presence of antigens in tissue. It is based on the chemical reactions produced by enzymes (either HRP or AP) conjugated with either the primary or secondary antibody.  

• Challenges arise in visualizing both rare and highly abundant targets on the same slide due to a narrower dynamic range. 
• Challenges also arise when differentiating between mixed and single colors when targets co-localize. 
• Broader emission spectra and fewer color choices as compared to fluorescent dyes makes multiplexing difficult.