HI all,
I have been for about a year trying to visualise my nitrogen-doped graphene quantum dots (sized less than 10nm) via TEM. Out of the many tries I have done it, I was only successfully able to image it without any contrast agent once. But further repeats of the imaging were not successful. I would like to describe my issues here:
1. The grid keeps on peeling and I am not able to see any retained GQD. Perhaps one reason could be that I had drop casted close to 40uL (a few drops) on the grid, that it might have been too harsh on the grid? I have imaged other nanoparticles (PLGA-based, iron oxide, SDS micelles, etc.) and I did not have this issue.
2. Since my GQDs are carbon based, contrast is an inherent and expected issue. For this, I tried staining my sample with 1% phosphotungstic acid and then sonicate before drop casting. The results was weird, with what seems to be my GQD being aggregated onto another particle. (kindly refer to image attached)
3. There was only once I could successfully image my particles and that was because I was lucky enough to locate one tiny region where my grid was intact and I quickly took images of my GQD.
Note: "TEM images compile 2" is the one successful run of my sample. This is the expected size of my sample
I would really like to hear from those who would have imaged carbon or graphene quantum dots to see how the sample can be prepared optimally for successful visualisation every time the TEM is done!
Thanks and Regards,
Mathangi
Hello Mathangi,
In order to image GQD, the first choice is to select an appropriate mesh/TEM grid. Mostly lacy grids are used for C-based nanomaterial analysis.
Also, while preparing the solution you need to keep the concentration very low and then sonicate it for a longer duration (atleast 2-3 hrs) to ensure you get a better dispersion state and less agglomeration. And then, take only a single drop (if your concentration is very low then you can take 2 drops from the dropper) of the solution on the grid. Also, the grid should be fully dried before imaging. Another point to consider is to disperse the GQDs in an organic solvent like ethanol rather than using DI water.
Hope this helps!
All the best!
Akanksha Adaval thank you for the input! May I check by single drop, do you mean with a micropipette or Pasteur Pipette? What volume should it be roughly?
and would overnight be enough for the grid to be fully dried? I leave it out at the lab bench. perhaps should I try drying for two days?
Sure, I will check out appropriate grids, are there any specific models or manufacturera you recommend? Thank you once again!
Single drop through a dropper. I didn't use pipette for that and so can't tell you the volume used. You need to dry the grid in vacuum oven at around 70-80 C depending on if you used ethanol. Higher temperatures for longer duration usually damage the grid. Room temperature would not be enough to completely dry it. Better use a vacuum oven or even normal oven can work.
Sorry, I have no idea about models or manufacturers of grids.
The preparation of graphene quantum dots for TEM analysis can be challenging, as the particles tend to be small and can aggregate easily. Careful sample preparation is essential for obtaining accurate and reliable results.
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Sajjad Janfaza thank you for the advice. May I check with you on what concentration and volume of PTA should I add to the grid for contrast? I have 1% of PTA diluted in water. Can I add 10uL of it onto the grid? And should I just let it dry overnight and then I can image?
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