Pre-embedding labeling methods.

Colloidal gold conjugates generally do not readily penetrate cells, even after permeabilization. Therefore, their use in pre-embedding immunostaining has been largely restricted to labeling cell-surface antigens for scanning or transmission electron microscopy or for tracing endocytic pathways in living cells. One nanometer gold conjugates that do penetrate cells and tissues much more readily have also been used successfully to immunolabel intracellular structures. For pre-embedding labeling, all of the immunostaining is done prior to embedding the tissue in resin or preparing the samples for scanning electron microscopy. This chapter provides methods for pre-embedding staining with unconjugated primary antibody or with primary antibody conjugated to colloidal gold. The use of colloidal gold for tracing endocytic pathways is also given.