מיקרוסקופ אלקטרונים של אימונוגולד

In immunogold electron microscopy, a target molecule is labeled using gold-conjugated antibodies.

The gold increases the electron scattering to give high-contrast dark spots. These spots can be distinguished from the other unlabelled structures and allow localization of the target molecule.

Direct immunolabeling uses a gold probe attached to a primary antibody that directly binds to the target molecule. 

Indirect labeling uses a gold-labeled secondary antibody that binds to an unlabelled primary antibody. Indirect labeling is used more often due to its higher sensitivity.

Immunolabeling can be performed using several different techniques — post-embedding, pre-embedding, or whole-mount.

In the post-embedding technique, a sample is embedded in resin and then sliced into ultrathin sections that are then treated with gold-labeled antibodies.

In the pre-embedding technique, a sample is first incubated with the gold-labeled antibodies and then resin-embedded and cross-sectioned.

The whole-mount technique does not involve resin-embedding. Antibody reactions are carried out directly on a sample placed on the sample holder.