The cheapest way I know, without also losing any exosome content, is using a cushion of sucrose 30% during ultracentrifugation. Sucrose at 30% and exosomes have a similar density and thus the sample ends up a bit cleaner.

My ultracentrifugation tubes have a total volume of 20ml. I add 2ml of Sucrose 30% and then I add the supernatant from cell culture, carefully and without disrupting the sucrose cushion.

Here is the paper:

Article An improvised one-step sucrose cushion ultracentrifugation m...

Thank you very much for your reply. You used it for the medium (what volume do you use for ultracentrifugation?). Is about 1 ml of platelet supernatant enough to mix with sucrose? Does any ratio of supernatant to sucrose have to be kept?

You don't mix it, Joanna. You have to carefully overlay your medium on top of the dense sucrose solution.It is enough if the sucrose medium is about 10% total tube volume. If your UCF tubes are much bigger than few mL, you should dilute your platelet supernatant with PBS and then put it over sucrose solution.