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Do you guys degas the ddH2O? You will oxidize the magnetite with that many wash steps unless the water is fresh as.
My building is a million years old and the ddH2O is always a little acidic, It gets distilled into a massive tank and stands for a while before getting it out of the tap.
Plumbing is probably full of who knows what but I do have a Milli-Q machine available, but the pH is always quite low out of the Milli (~6.3) and drops over time as it takes on CO2 .What do you make of the prospect of buffering the ddH20 with PBS or god forbid TRIS or just a degas? I ran out of time and was to lazy to refill my LN2 N2 generator but managed to save face with a drop of NaOH. But bumping it just above 7 might be a good idea.
Hi R B,
No need to adjust pH. The Alkali solution will take care of that. The iron solution is also kept acidic (with HCl), to avoid iron oxide precipitation. We do degas the solutions using a vacuum pump and heat up the alkali to ~80C. Initially we were flushing the reaction bottle (and the solution) with N2, yet if it is degassed and preheated, you can also skip N2.
If you observe that the uncoated MNPs during washing are getting dissolved (the supernatant from wash turns slightly brown), it usually means that there was too much O2 in the system. In such a case I would indeed recommend flushing (bubbling) the solutions with N2 for at least 30 min.
Hope this helps,
Good luck with synthesis,
T
Step 3 of this protocol mentions using 10 mL of a 35% ammoniac solution. Is this just a typo referring to the 25% ammonia solution? Also, would you recommend preparing this solution from 7 M NH3 in MeOH?
Dear Egan,
Right. Thank you for spotting the typo, will correct it in the new version (indeed it should be 25%). Whether 7M NH3 in MeOH can be used instead, I don’t know. In principle the MNPs are already formed in the NaOH solution, thou I don’t know what effect the extra MeOH could have on the final reaction. In principle one could test it (or compare to the standard 25% ammoniac) in a smaller scale synthesis.
Hope this helps,
Tomek
Thanks for this awesome protocol 🙂
We got lovely magnetic beads after step 4 of the protocol…but the beads progressively became less and less magnetic during the MilliQ H2O washes.
I guess the culprit is our MilliQ water – its pH is 5 :-S
Along the lines of what R.B. suggested in reply #1942, could you suggest using buffer (which one?) instead of H2O for the washes?
Thanks in advance
Is the soloution opaque or translucent and drak brown tea? Like the magnetite pellets on your magnet and the soloution is transluent but coloured? or its just opaque and pellets aswell?
You might just need a better magnet, I got a 30x30x15mm n52 beast and it will clear the soloution now no worries. You will probably need to do the synthesis again or wash them until it goes clear and no yellow/brown colours and sonicate to disperse again because they go bad fast until coated.
Try centrifuging if you dont want to get a staunch magnet they are a bit wild and it almost works better for dense soloutions of magnetite.
Right after synthesis, in alkali conditions, the magnetite pelleted on the magnet completely and quickly.
During the washes in H2O the magnetite pelleted more and more slowly, until it hardly pelleted anymore. The supernatant became progressively more brown in color.
We just ordered a better magnet.
Is it normal, though, that the magnetite pellets less efficiently or is this a sign of oxidation? We will use degassed H2O in any case next time (but would buffer be better?).
Thanks for the tips!
Dear MCGambetta,
Well, we encountered a trouble like this when there was too much oxygen in the alkali solution or the iron II/III mixture was not well mixed. What I can recommend is to prepare the iron solution then mix it and filter with a 0.2 or 0.45 filter. The alkali solution we degas and heat up to ~80C which took care of the problem.
In principle the MNPs should not be too fragile and we coated them even after storage for 1-2 weeks after synthesis. The brown solution (at least what we think) suggest that the synthesis did not go optimally and the particles are small and fragile to oxidation.
Just give it a try in a smaller scale with degased and preheated solution and have a look if this got improved.
Best luck,
Tomek
What we noticed is that the brown colored liquid is also magnetic (yet sediments much slower). We think that these are disrupted, small MNPs. We did not try to use them for coating, rather we made fresh MNPs that were stable (as described above),
Cheers,
Tomek
Is it at all possible to perform this protocol if I don’t have a nitrogen or argon source to perform the experiment in inert conditions? Does anyone have suggestions in this case?
Dear William,
There is no need for N2 or Argon! You should degas and heat up the solutions to ~80C and the synthesis should work. Degassing and the heat gets rid of a large part of O2 in the solution and does not disturb the synthesis too much.
Best regards,
Tomek
Dear all,
I’m also having some problems with the washing steps. Right after synthesis, the MNPs are quickly attracted to the magnet rendering the supernatant completely clear. Subsequent washing steps however, give rise to an increasingly dark colored solution.
I have tried degassing the water with N2 (with a homemade contraption) and also boiling it to remove most of the dissolved oxygen. For practical reasons, I did let the water cool down first in a Schott bottle and after opening it seemed to have been an airtight seal. Would it make sense to do the washing steps with 80°C water?
Is it possible that I introduce too much oxygen into the system when I dissolve the magnetic pellet by shaking too vigorously? Or are there other potential pitfalls I should pay attention to?
Thank you very much in advance!
Kind regards, Jonas
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