Characterization of Extracellular Vesicles by Transmission Electron Microscopy and Immunolabeling Electron Microscopy

Transmission electron microscopy (TEM) is currently the only method that enables the observation of extracellular vesicles (EVs) at a nanometer scale. Direct visualization of the whole content of EV preparation provides not only crucial insights on the morphology of EVs but also an objective evaluation of the content and purity of the preparation. Coupled to immunogold labeling, TEM allows the detection and association of proteins at the surface of EVs. In these techniques, EVs are deposited on grids and are chemically immobilized and contrasted to withstand a high-voltage electron beam. Under high vacuum, the electron beam hits the sample and the electrons that scatter forward are collected to form an image. Here, we describe the steps needed to observe EVs by classical TEM and the extra steps required to label proteins through immunolabeling electron microscopy (IEM).