Initially colloidal gold was 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 key benefits 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.
The key features of gold conjugates are:
- For TEM, any particle size may be used, the smaller particles giving the highest labelling efficiency.
- For 2nm and 5nm gold conjugates a combination of gold labelling with silver enhancing will yield larger size particles with high labelling intensity.
- EM grade conjugates are available in a range of sizes.
- All sizes are completely non-overlapping, with the narrowest available coefficient of variation to allow multi-labelling experiments.
- For low magnification work, larger particles (15 - 30nm) are more easily seen.
- Small gold particles (5 - 10nm) are well suited to high magnification studies and high intensity labelling.
- 10nm gold conjugates are recommended for those just beginning immunogold labelling with EM and performing studies over a range of magnifications, whereas 2nm gold particles offer ultra high sensitivity, but are usually visualised only after silver enhancing on the section.