Postembedding Labeling Methods

Since it was first introduced (1 ), postembedding immunogold labeling has become the most widely used method of immunolabeling for electron microscopy (2 –8 ). 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, and so forth. Colloidal gold has several advantages as a marker for electron microscopy. The gold particles are distinct and readily visualized, they are easily quantifiable, and they do not diffuse on the sections.