Using Protein A Gold or Immunogold reagentsMarking of cell surface and intracellular components for microscopical observation is an extremely important technique for studying molecular organization and cell function.
Gold is sufficiently heavy to impart electron-density to biological macromolecules and thus is widely used in a variety of receptor and tracer applications. In immunogold labelling, gold markers are used for indirect labelling of specific sites. First, specific immunoglogulins are allowed to react with the antigen to be studied and subsequently the marker is bound to the specific immunoglobulin, using either Protein A- or a second immunoglobulin.
Protein A Gold
Protein A is a cell wall constituent produced my most strains of Staphylococcus aureus. From the viewpoint of immunochemistry the most interesting property of protein A is its unique ability to interact with immunoglobulins, notably immunoglobulin G. Protein A has been shown to be a useful reagent for binding immunoglobulins from several animal species, a property which renders this protein of general applicability in immunocytochemistry.
Methods for multiple labelling of the same specimen with colloidal gold particles
of different sizes are also available.
Although post-embedding labelling is most common, it can be used for pre-embedding immunolabelling. Thin conventional sections as well as thin cryosections can be labelled with colloidal gold.
Ultra Small Gold
Ultra small gold (<1.0 nm) conjugates provide a marker system that has greater labelling sensitivity and better penetration than larger gold particle conjugates. This advantage, along with the availability of silver enhancement reagents, have made it possible to apply pre-embedding immunogold/silver techniques to the localization of intracellular antigens with great success.
Immunoelectron microscopy using colloidal gold is used to advance morphological diagnosis, including virological, by the in situ localization of cellular macromolecules. This information is used to elucidate biochemical properties and functions of cellular compartments and components.