Colloidal gold was first introduced as a cytochemical marker for TEM in 1971 by Faulk and Taylor*, and has become the universally accepted label of choice for electron microscope immunocytochemistry applications and detection of cellular and subcellular macromolecules. It is now a well established technique. Gold labels combine the benefit of unequivocal identification of antigens together with high resolution localisation. The wide choice of gold particle sizes available for labelling at different working magnifications, together with its quantitative facility, also make gold labelling a very flexible tool. One of the major advantages of colloidal gold for electron microscopy is its high electron density, offering easy detection. Procedures for using gold reagents are now well established, and these techniques have been proven to be simple, efficient and economical, as well as non-hazardous.
For SEM 20, 30 or 40nm maybe used together with back scattered electron imaging.
For smaller particles sizes see Gold Conjugates - TEM