Immunogold

Immunogold labeling is a technique used to localize specific antigens within cells or tissues by attaching small gold particles to antibodies. The gold serves as an electron-dense label that can be detected with electron microscopy, revealing the precise subcellular distribution of the target protein or molecule.

The method relies on antibody-antigen binding. In direct labeling, a primary antibody is conjugated directly to a colloidal gold particle. In indirect labeling, an unlabeled primary antibody is followed by a secondary antibody or protein A/G that carries the gold particle. Common colloidal gold sizes range from about 1 to 20 nanometers, with smaller particles allowing higher labeling density and larger particles enhancing visibility.

Samples are prepared for electron microscopy, typically involving fixation, dehydration, and sectioning of resin-embedded tissues or preparation of cryosections. Immunogold labeling can be performed on both resin-embedded sections and on cryostat or cryosections, with protocols optimized to preserve antigenicity. After labeling, samples are examined by transmission electron microscopy; gold particles appear as discrete dark spots, indicating the location of the antigen. For light microscopy or enhanced detection, silver enhancement can be used to enlarge gold particles and improve visibility, sometimes followed by gold enhancement for multiplexing.

Applications include precise localization of proteins at the ultrastructural level, quantitative analysis of labeling density, and multiplex imaging using particles of different sizes to tag multiple antigens. Immunogold labeling is widely used in cell biology, neuroscience, and pathology, though it requires careful optimization of fixation, labeling conditions, and appropriate controls to ensure specificity and accuracy.