We are running out of the stock of 2x PEI pH7 (polyethylenimine), that was created a long time ago in a galaxy far, far away. I don't even know the actual concentration of that and I think no one does. So we need a new one.
Generaly I learned, disolving PEI is a pain in the ass, many people can't do it, many just dilute it partially, for many it does not work or stops working. Many different polymers, branched, linear... There are arguments against using the usual ph7 neutral solution and use acidic instead, some cells don't like those etc. There are many types of PEI and many protocols. I just want it to work, reproducibly, being a best cost-effective transfection reagent doesn't matter that much. I'm getting lost in it a bit
I found these options:
Polyscience Polyethylenimine, Linear, MW 25000, Transfection Grade (PEI 25K) [kat. no. 23966] - 315 EUR for 1g, that is for common concentration 1ug/ul a liter of PEI, which is kind of overkill, unbranched according to image
Sigma Polyethylenimine, branched (average Mw ~25,000 by LS, average Mn ~10,000 by GPC, branched) [kat. no. 408727] - 108 EUR for 100ml of highly viscose stuff
(paper mentions just diluting it in water and that's it, not sure how to calculate it, density mentioned 1.030 g/mL, and it is supposed to be a 100% solution)
Sigma Poly(ethyleneimine) solution, 50 % (w/v) in H2O, aparently branched (mentioned Mw 750,000) [kat. no. P3143] - 79 EUR for 100ml, which should be solution containing 50 g of PEI, so far the easiest to dissolve, as users say, but I'm bit unsure about the very different Mw than the others, it's very high
One other I found, Polyscience offers their "upgrated PEI 40K" as a ready-to-use solution of 1mg/ml PEI, called Transporter 5 [kat. no. 26008] - overall 5 mg for 95 EUR, they call the PEI 40K more reliable (cost for 1 g of powder is similar as above) but I haven't found much of a citations for this, except for one guy saying it didn't work.
So far I'm most interested about Sigma 50% w/v solution which should be just dissolved, but not sure in what, some use 15mM final concentration Hepes, some use just water. Except for the different Mw it seems best option. Also as it is not average, it may be more homogenous, I've heard many people saying different lots of PEI work/not-work differently. I'd like something working the same when diluted, but the Transporter seems to be quite pricy.
Which one do you use realiably with a specific way of preparation? (mostly I see protocols for the Polyscience 25K powder, but that is maybe cheap in overal but is is a lot to pay at once, I'd like to avoid it)
Thanks for any suggestions.