Exosome investigation: the approach of electron microscopy

A mixture of cell-derived extracellular vesicles (EVs) are contained in the extracellular environment, in particular body fluids. The EVs originate from the lipid membranes of a variety of cells and are engaged in the intercellular communication in a broad range of physiological processes and pathological conditions. The smallest type of EVs, exosomes, with sizes ranging from 40 nm up to approximately 100 nm in diameter, originate from the endosome. Exosomes are natural nanoshuttles that are capable of delivering their cargo of RNA, lipids, and proteins to cells in close proximity and to distant cellular destinations. There is a rapidly growing interest in utilizing exosomes present in patient biofluids in view of their potential for molecular diagnostics in the clinic or as potential carriers for drug delivery. In this context, an appropriate use of electron microscopy is extremely important for characterizing materials at a length scale of few nanometers. Microscopy analysis facilitates our understanding of exosome biogenesis and cellular uptake, as well as allows the purpose of developing future exosome-based diagnostics and therapeutics.