Looking for recommendations for an exosome extraction kit for cell culture supernatant, sample volume around 30 ml.

For 30-40ml of cell supernatant, if you are only doing Western blot and NTA, the precipitation method can be used, but do not directly take the precipitate to run NTA, as contaminating protein particles will raise the background. I generally use PEG-based precipitation, then resuspend in PBS and pass through a 0.22μm filter, which makes NTA much cleaner. The precipitation method usually has a higher recovery rate, but its purity is not as good as membrane affinity. If you need it delivered to Hangzhou this week, choose an agent with a local warehouse and ship via SF Express, which can basically arrive in 1-2 days. For a budget within 80 yuan per run, the precipitation method is sufficient, while membrane affinity may exceed it. Before placing an order, confirm with the sales representative that it is in stock, and do not wait for transfer from another location.

I suggest not buying a large box all at once. Ask the manufacturer to send a small trial sample, and use the same batch of tumor cell supernatant split into three aliquots: parallel extraction by your existing ultracentrifugation, precipitation method, and membrane affinity method. Look at total protein, CD63/TSG101, Calnexin negativity, and the NTA particle size/particle number ratio. This way you can determine whether the recovery rate is sufficient and how much contaminating protein there is, which is more useful than simply comparing prices. Many reagent distributors in Hangzhou have stock available, and you can request delivery within this week. The trial sample cost can usually be credited toward a subsequent full-size purchase, so ask clearly first.

If purity is the priority, I would recommend membrane affinity or size exclusion chromatography, especially since you will also be doing NTA downstream. You can first take 30 ml of supernatant, remove cell debris at 3000g, concentrate to about 5 ml using a 100 kDa ultrafiltration tube, and then run it through a membrane affinity column. This will give a lower recovery rate than the precipitation method, but the particle size distribution and WB negative control will be cleaner. If the per-run cost must be kept at 80 yuan, domestic small-format options have a better chance, while imported columns will most likely exceed the budget. As for supply, ask the Hangzhou distributor to ship via SF Express, which can go out the same day and arrive very quickly.

For 30 ml of supernatant, the precipitation method is the simplest, but it contains many contaminating proteins, so purification is required for subsequent WB.

Ultrafiltration concentration followed by ultracentrifugation is recommended. 30 ml is not considered large, and a certain imported S kit is also OK.