@jonasds
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Dear Tomek,
Thank you for your kind reply, maybe the age/quality is indeed the issue because I have the impression that the washing steps are going even worse than before…
I think I’ll just have to bite the bullet now and order pre-made paramagnetic beads which I can then use with the different protocols your team has developed. If that all works out, we can still try to synthesize beads ourselves at a later time.
Thank you for your help!
Kind regards, Jonas
Dear all,
After a long hiatus, I tried the protocol again, paying attention to the different critical points. I filtered my iron salts solution to have a perfectly clear solution to start with, degassed the solutions using sonification and also adjusted the pH of the water.
But again, I’m having the same problem: after a few washes the solution gets increasingly dark.
I took some of the bead solutions and checked them with the light microscope (400x magnified) and I can see a lot of irregular large pieces. They do seem to react to the magnetic field, but their presence must indicate I did something wrong during synthesis right? I have included 2 external links for pictures here:
Thank you for your help.
Kind regards, Jonas
Dear Tomek,
Thank you for taking the time to exhaustively answer my questions.
I will try the protocol again when I have some free time in the lab (might take some time though) and I’ll report back here.
Thank you again!
Kind regards, Jonas
Dear Tomek,
Thank you for your fast reply! And don’t get me wrong, I’m very happy that you and your team have made this protocol available to the research community. It would be a really great way to stretch our budget.
1) If the ratio would be wrong would I still get a magnetic precipitate before washing? Or does the faulty ratio cause MNPs that easily break down?
2) I will definitely filter the solution next time first. I did not see any real precipitate, but it wasn’t translucent either, it had more of a (slightly) cloudy appearance.
3) I’ll include these steps again in my next trial.
4) I’ll check the pH of the water (UPDATE: it turned out to be around 5.8) and if necessary I’ll use Tris buffer maybe (pH8?), is the use of Tris expected to interfere with the silica coating protocol?
Is it also important how quickly the iron salt solution is added to the sodium hydroxide? I don’t have a burette in the lab so I use a Pasteur pipette and I try to add the solution in a dropwise fashion.
Thank you again for the help and the beautifully documented protocols!
Kind regards, Jonas
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
