For extracting exosomes from 50 mL of cell supernatant, which is more cost-effective: the precipitation method or ultracentrifugation?

I have used domestic precipitation kits for MSC and tumor cell supernatants, centrifuged overnight at 4°C, and the pellet was visible to the naked eye, but if WB samples were loaded based on experience, the area beside the CD63 band was sometimes smeared. Later, I aspirated the supernatant as thoroughly as possible after centrifugation, then added PBS to resuspend and centrifuged again at 10,000g for 5 min, and lysed the pellet; the background of contaminating proteins decreased considerably. In terms of reagent usage, 50 mL of supernatant usually needs to be scaled up by volume, and it is recommended to first calculate the consumables and number of centrifuge tubes needed per run. For the per-run cost, ask the distributor for a quotation on small specifications and convert accordingly; one box of a domestic kit can generally process multiple 50 mL samples, but the exact number depends on the volume ratio. Do not look only at the price; it is recommended to also buy an imported kit or an ultracentrifugation sample as a control, otherwise the WB results cannot be judged.

I also switched from ultracentrifugation to precipitation before. A 50 mL batch really gets stuck waiting in line for the centrifuge, which is frustrating. The precipitation method requires less hands-on time per run, but the extracted samples become sticky, and the background is dirtier for electron microscopy, NTA, and WB. To be more cost-effective, I suggest splitting the 50 mL into two workflows: keep 20 mL for ultracentrifugation or density gradient as the "gold standard" quality control, and use the remaining 30 mL with a precipitation kit for routine WB. This saves time without completely losing morphological data. Precipitation kits usually have decent recovery rates, but the particle counts may not represent true exosomes. For WB, it is best to first quantify by total protein rather than loading equal volumes directly. For domestic kits, you can ask the manufacturer for NTA or WB examples from cell supernatant first; many brands are willing to provide trial samples.

When choosing a domestic precipitation kit, don't just focus on the "price per box." Look at: 1) whether it distinguishes urine/plasma/cell supernatant; 2) whether pre-concentration is required, as a 50 mL sample may need to be divided into multiple tubes; 3) whether a wash solution or purification column is included after precipitation; 4) whether it is compatible with subsequent RNA/protein extraction; 5) whether the manufacturer can provide quality control data for the same lot or multiple lots. With a budget under 2,000, you can usually buy a small kit for cell supernatant, but before purchasing, it is advisable to run a small pilot test with your own tumor cell line to observe whether the pellet is easy to resuspend after precipitation and what the protein background is like after lysis. Lot-to-lot stability is also critical, especially for long-term WB work, where fluctuations in precipitation efficiency between kits can affect band intensity, so it is best to fix one lot or perform quality control after arrival.

For 50 mL of cell supernatant, the precipitation method is indeed more flux-friendly than ultracentrifugation, especially when there is no multi-rotor or when there are many sample batches. For per-sample cost, do not look only at the kit unit price; calculate based on the actual starting volume: some kits require several tubes for 50 mL of supernatant, so the cost rises quickly when processing 5 samples. It is recommended to first buy a small size or apply for a trial pack, and use the same batch of tumor cell supernatant for a parallel comparison between ultracentrifugation and precipitation. The biggest problem with the precipitation method is not recovery, but that contaminating proteins co-precipitate. Before WB, it is best to resuspend the pellet in PBS, centrifuge and wash once, and run CD63/TSG101 and Calnexin at the same time. Domestic brands are commonly under 2,000, but check whether the instructions explicitly support cell supernatant and whether they specify the culture requirements for serum-free exosome production.

If the downstream application is only WB, the precipitation method is actually acceptable, but it is recommended to adjust the sample preparation first. Many of the reports of high impurity protein levels come from direct lysis and loading after extraction, where residual polymers and serum proteins interfere with BCA quantification and electrophoresis. It is recommended to wash twice with 1× PBS after precipitation, then lyse in a smaller volume of lysis buffer for the final step; after BCA quantification, control the loading amount per well to 10-20 µg total protein, and include a Calnexin negative control. If the Calnexin signal is stronger than that of exosome markers, the purity is insufficient, and subsequently the sample can be passed through a small-volume size exclusion column or subjected to ultrafiltration buffer exchange. When choosing a domestic precipitation kit, prioritize asking whether it has a dedicated impurity protein removal step for cell supernatant, rather than only looking at the price. It can be found within a budget of 2,000, but batch-to-batch stability must be verified by yourself.