Division of Radiooncology, Deutsches Krebsforschungszentrum, 69120 Heidelberg, Germany
Apart from fluorochromes and enzymes, other markers are available for immunohistology with main interest in ultrastructural studies. One of such markers is colloidal gold (FAULK WP and TAYLOR GM, 1971). Even if originally developped for the electron microscope, gold labels have also proved useful for light microscopy. A range of proteins such as antibody molecules, protein A and streptavidin can be easily coated with uniform gold particles of various sizes; a range from ultra small colloidal gold reagents (<1 nm) to gold reagents in the order of >25 nm are commercially available. Gold labels can be detected in the light microscope by bright field illumination from pale pink to deep red, depending on the strength of reaction. With modern silver enhancement methods, gold particles become coated in metallic silver giving a brown-black color. Gold labels are compatible with many histological and histochemical stains.