Atomic force microscopy analysis of extracellular vesicles.

Extracellular vesicles (EVs) are small vesicles ensuring transport of molecules between cells and throughout the body. EVs contain cell type-specific signatures and have been proposed as biomarkers in a variety of diseases. Their small size (<1 µm) and biological and physical functions make them obvious candidates for therapeutic agents in immune therapy, vaccination, regenerative medicine and drug delivery. However, due to the complexity and heterogeneity of their origin and composition, the actual mechanism through which these vesicles exert their functions is still unknown and represents a great biomedical challenge. Moreover, because of their small dimensions, the quantification, size distribution and biophysical characterization of these particles are challenging and still subject to controversy. Here, we address the advantage of atomic force microscopy (AFM), for the characterization of isolated EVs. We review AFM imaging of EVs immobilized on different substrates (mica, glass) to identify the influence of isolation and deposition methods on the size distribution, morphology and mechanical properties of EVs.