Tyramide signal amplification is an enzyme-mediated detection method that uses the catalytic activity of horseradish peroxidase (HRP) to generate high-density labeling of a target protein or nucleic acid sequence in situ. The TSA Kit #22 includes HRP—streptavidin and our exceptionally bright, photostable green-fluorescent Alexa Fluor 488 tyramide (which is spectrally similar to fluorescein).