Practice question

Immunoelectron microscopy localizes antigens at ultrastructural level by conjugating antibodies to electron-dense colloidal gold particles of 5-20 nm diameter. Gold strongly scatters electrons, appearing as black dots in TEM, pinpointing protein distribution within organelles. Unlike fluorophores used in confocal or fluorescence microscopy which bleach and lack electron contrast, gold provides stable, quantifiable label for high-resolution mapping. Antibodies linked directly or via protein A-gold complexes enable double labeling with different sizes, essential for studying trafficking, vesicular transport, and cytoskeletal-associated proteins with nanometer context.