Characterization of rat exosome-bead conjugates by electron microscopy. Electron micrographs of magnetic beads immunologically coated with exosomes. Beads were coated with vesicles of 60 nm average diameter. Most vesicles were filled with electron-dense material (A) (bar, 1 μm). The beads were uniformly coated with vesicles, with most of them directly attached to the beads. Some vesicles appeared to be extracted and partially flattened (B).