Tyramide signal amplification is an enzyme-catalysed deposition of tyramide on or near a protein or nucleic acid in situ. The enzyme horseradish peroxidase (HRP) converts the labelled tyramide substrate into a highly reactive form that can covalently bind to tyrosine residues on target molecules at or near the HRP, in the presence of low concentrations of hydrogen peroxide. Labelled FITC-tyramide reagent enhances both the fluorescent and colorimetric detection sensitivity. FITC-tyramide is used in multiplex immunohostochemistry (IHC) and Fluorescent in situ hybridisation (FISH). FITC-tyramide is useful for detecting marine picoplankton, in situ imaging of proteins and studying the effects of reactive oxygen species on extracellular matrix proteins.