2.13. Transmission Electron Microscopy (TEM) Measurements

A drop of each EVs sample was deposited onto a 300-mesh copper grid for electron microscopy covered by thin amorphous carbon film (20 nm). TEM grids were placed on a teflon tape and samples were incubated for 20 min to obtain a high particle concentration on the grid. The excess of liquid was removed by touching the grid with filter paper. Before the samples were completely dried, 10 µL of 2% aqueous phosphotungstic acid solution (pH-adjusted to 7.3 using 1 N NaOH) was deposited on the grid and removed by filter paper after 2 min.

Measurements were carried out by means of a FEI TECNAI 12 G2 Twin (FEI Company, Hillsboro, OR, USA), operating at 120 kV and equipped with an electron energy filter (Gatan image filter, Pleasanton, CA, USA) and a slow-scan charge-coupled device camera (Gatan multiscan).