Used as a staining agent in electron microscopy to enhance contrast of biological specimens, particularly in the visualization of cellular ultrastructure. It binds to cellular components such as membranes and macromolecules, increasing electron density and improving image resolution. Commonly applied in the post-staining step after uranium-based stains to provide detailed imaging of organelles, nucleic acids, and protein complexes. Its effectiveness in highlighting fine structural details makes it a standard reagent in biological and medical research involving transmission electron microscopy.