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Hi,
I came across you nice article in PLOS Biology. Making magnetic beads ourselves would solve a lot of problems on our side. Thank you for making these protocols.
I made the magnetic particles today. Similar to others, with the second and third water wash the water got black /brown. I could pellet the beads but it seemed like they are dissolving.
I bought new reagents beforehand, I degassed all the solutions with a vaccum pump for 1h. I heated the 2M NaOh solution to 80 degrees and also the Fe2/3. I filter sterilized the Fe2/3 solution and then degassed it for 1 h. It was clear and light yellow. However when I heated the Fe2/3 solution it darkened and got orange. After adding the Fe2/3 drop wise with a pasteur pipette to the 2M NaOH, the Fe2/3 bottle contained some white/yellow stuff at the walls. I assume that the Fe2/3 solution underwent some reaction during the heating.
My questions are the following:
1) Which solutions need to be degassed and heated? Is it only the 2M NaOH? Or is it also the Fe2/3 and the water for the washes.
2) After adding the ammonium solution and waiting for 30 min, I switched of the heating and soon started the washing. Is it necessary to cool the solution slowly to finalize the reaction?
I hope you are still answering questions to this protocol.
Ahoy,
I have myself encountered this problem and do not fully understand why it sometimes occurs but not always and not for everyone. But it is most certainly the result of Oxygen/oxidation. Aside from the usual recommendations which you seem to have already adhered to I can at this point only recommend to find the means to perform your synthesis under inert gas. Or alternatively, to employ a coating/capping agent such as Oleic acid.
There are a number of publications easily found which use Oleic acid (OA). While we do not have a proper protocol for you at this point I can tell you that the addition of OA, post initial Fe solution precipitation, while otherwise sticking to our protocol should work and may solve your issue.
I will talk to my colleagues and see whether they have some further recommendations.
Best regards
Tim
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