Pre-embedding labelling
This technique is based on introducing the primary and secondary antibodies with gold tags into the specimen while it is still hydrated.
It requires permeabilisation of cell membranes with detergent after primary fixation in order for the antibodies to penetrate into the cell and reach the epitopes. Because the labelling is performed immediately after primary fixation the sample can subsequently be prepared as conventional ultrastructure preparations, i.e. with osmium postfixation and epoxy resin embedding, sectioned and imaged. In this way we combine epitope preservation with relatively good contrast and specimen stability compared with other immuno techniques.