For primary cell transfection, which endotoxin-free plasmid extraction kit has the lowest residual?

<p>When we do primary neuron transfection, we mainly look at the batch-to-batch stability of endotoxin-free maxiprep kits. If the copy number of a 200 mL bacterial culture is normal, I will prioritize trying MN NucleoBond Xtra EF or Omega&#039;s Endo-Free maxiprep. When using a vacuum manifold, keep the negative pressure at around -20 to -30 kPa; don&#039;t pull too hard. After obtaining it, don&#039;t apply it directly to cells; first take a small amount of the eluate and retest it with the LAL assay; if the requirement for endotoxin</p>

We previously encountered poor primary cell status when using standard large-scale plasmid prep, and later switched the plasmid extraction kit to one with an endotoxin removal step, and tested LAL for every batch. When selecting, it is recommended not to only look at the "Endo-free" label, but to check the endotoxin removal principle in the instructions: whether it is selective adsorption resin or ion exchange column; also check whether the maximum bacterial culture volume covers 200 mL and whether it is compatible with vacuum. I have retested the EF series from MN and Omega, and they can generally achieve below 0.1, but not every batch is the same, and it is related to bacterial culture OD and lysis time. After the kit arrives, first perform a preliminary test with 200 mL bacterial culture, take 300 µg plasmid for endotoxin testing, and then use it for primary neurons, which is relatively reliable.

With a budget of 1500, if you want to buy an imported maxiprep endotoxin-free kit, you may need to be selective about the channel. Qiagen is relatively expensive, while certain specifications from MN and Takara are more budget-friendly, but for delivery within 3 days, it's best to have the sales rep confirm local stock rather than just relying on the e-commerce page. Another angle: if the kit arrives slowly, you can first resuspend the bacterial culture in P1 containing RNase and then freeze it or store it briefly at 4°C to avoid repeated freeze-thaw cycles. If only regular maxiprep kits are in stock, it's not advisable to force a prep for primary cells; you can ask a lab in the same city to borrow an endotoxin-free column for emergency use. When selecting, also clarify the maximum yield—200 mL is generally sufficient for high-copy plasmids, but low-copy plasmids may require combining two tubes.

If your system must be used with negative pressure, first confirm during selection that the column inlet/outlet can connect to a standard vacuum manifold and that the column body will not deform under negative pressure. I have used an imported endotoxin-free large-scale plasmid extraction column connected to negative pressure and found that when aspiration is too fast, the column bed tends to dry out or channeling occurs, and ultimately the endotoxin residue fluctuates. In operation, it is recommended to aspirate slowly after adding liquid at each step, and stop when the liquid level approaches the column bed; do not aspirate the column to dryness. The elution buffer and collection tubes included in the endotoxin-free kit are generally subjected to endotoxin removal treatment, but the centrifuge tubes, pipette tips, and water you use yourself must also be endotoxin-free; otherwise, retesting will exceed 0.1. It is recommended to prepare several endotoxin-free 15 mL tubes to collect the eluate.