Colloidal gold is routinely used conjugated to ligands or antibodies as a label for the detection of cell structures by transmission (TEM) and scanning (SEM) electron microscopy. Silver enhancement, a procedure that amplifies the size of gold spheres, is used for light microscopic (LM) observation of colloidal gold. These techniques are valuable in localization studies but it is difficult to quantitate the level of labeling in larger volumes of tissue solely by microscopic means.
Instrumental Neutron Activation Analysis (INAA) can be used to provide a quantitative index of gold accumulation at the organ and tissue levels. Given that gold is not naturally found in the body in any substantial amount and that colloidal gold and ligand conjugates can be prepared to yield uniform bead sizes, the amount of label can be determined at the organ and tissue levels in whole animal systems.