I’m happy to see this questions, as with the rise of drug delivery research we’re opting to invest more application research into the exosome and extracellular vesicle workflows, so hopefully soon we’ll be able to provide some application material in the future.
Once clarified from the cell culture using depth, micro or diatomaceous earth filtration (or a combination of them depending upon the density and viability or your culture or lysate), I would first identify or make an estimate on the size distribution of your exosome diameter range. The guide provided in previous questions shows what ultrafiltration MWCO is best suited for what diameter. To capture all exosomes we would recommend picking a MWCO relevant to the smallest likely diameter of the exosomes. So with a likely range of 20 – 200nm, we would recommend using a MWCO of 50K, which can capture particles as low as 15nm. This will ensure that all exosomes, regardless of size are retained. Whilst still allowing small contaminating molecules to pass through the membrane, further purifying the sample as well as concentrating. It may be necessary to carry out a size exclusion chromatography step to further purify the exosomes, as by using a MWCO low enough to capture all the exosomes you may capture a larger amount of proteins above the MWCO also. With this in mind, you can always select a MWCO based upon the targeted exosomes size also, not just the minimum possible.