Postembedding Labeling Methods

Since it was first introduced, postembedding immunogold labeling has become the most widely used method of immunolabeling for electron microscopy. For postembedding labeling, samples are first fixed, embedded, and sectioned. All immunostaining is performed on sections mounted on grids. The immunostaining may be done with a direct labeling technique with the primary antibody conjugated to colloidal gold, or by an indirect method where the primary antibody is unlabeled and the gold is conjugated to a secondary or tertiary antibody, protein A, protein G, etc. Colloidal gold-antibody conjugates are also widely used, especially in indirect immunocytochemical methods. This chapter gives the standard method for post embedding labeling as well as one in which the cell membranes are enhanced.