The horseradish (HRP) conjugate of anti-fluorescein/Oregon Green® rabbit IgG antibody efficiently binds and quenches the fluorescence of fluorescein and Oregon Green® dyes. This antibody enables the use of fluorescein or Oregon Green® dyes as haptens instead of biotin. Unlike biotin, which is an endogenous ligand in mitochondria, dye-based haptens permit background-free staining of cells and tissues and a sensitive alternative to biotin-streptavidin methods. HRP conjugates are commonly used in histochemical amplification schemes such as the tyramide signal amplification (TSA) technology.