Negative Staining of Purified Exosomes: A Procedure to Visualize Exosome Morphology Using Transmission Electron Microscopy

In order to perform negative staining, fix the purified exosomes following isolation with 1 milliliter of 2% paraformaldehyde for 5 minutes. Treat thin formvar/carbon film coated 200 mesh copper EM grids with glow discharge for 1 minute. Then, load 5 to 7 microliters of the exosome suspension solution on a grid and incubate it for 1 minute. If the concentration of exosome is too high, dilute the concentration to an appropriate level.

Immediately, stain the exosomes with about 20 drops of a filtered 1% uranyl acetate solution on the surface of the EM grid. Remove the excess uranyl acetate solution from the grid by contacting the grid's edge with filter paper. Then, quickly rinse the grid with a drop of water.

Use a pair of tweezers to place the grid on the table, and cover the grid partially with a culture dish. Allow the grid to dry for 10 minutes at room temperature and then image the grid or store it in an electron microscope grid box for future observation.