Dear Bashir,

in your TEM image I rather see 2 populations of nanoparticles. Following the suggestion of Anant, I recommend to perform EDAX or EELS to check the chemical composition of the nanoparticles. Good luck.

Hi Bashir,

I agree with Daniel ie to consider that core may not even be there. But, there is also, one more limitation to a TEM i.e. if your particles are not spherical but flat, they may not show a good core. You could also increase the thickness of the coating on SPION, to get a more distinct core.

Apart from these, I dont know, but you could EDAX to confirm the presence of SPION in the core and GOLD on the sheath.

Hope this helps,

Good Luck

Dear dr daniel and anant,

am very gtaefull for your comments, attached is a copy of my tem showing the core-shell, gnp-spion. Further comment and recomendation will be highly appreciated

Dear Bashir,

in your TEM image I rather see 2 populations of nanoparticles. Following the suggestion of Anant, I recommend to perform EDAX or EELS to check the chemical composition of the nanoparticles. Good luck.

from my prior imaging of uncoated Spion the lighter image rep the naked SPION while the the darker and thicker is the spion coated GNP. thus i need to separate uncoated SPION via centrifuge.

How about checking the structure (XRD, SAED) of you NPs in combination to TEM? These should give you nice X-ray diffraction characteristic for Iron oxide, gold or iron oxide + gold, isn't it?

And attached is the uv-vis spectrum

I tried to make Fe3O4 core nanoparticles with a Au shell and ran into similar problems. My Fe3O4@Au nanoparticles were purple with a UV-vis spectrum peak near 563 nm. I tried electron mapping with EELS, but we could not obtain a strong signal for gold to offer any conclusive results. So I tried X-ray mapping and determined my sample was more of a iron oxide and gold nanoparticle composite. It appears that the gold nanoparticles were attached to the iron oxide particles much like what your posted TEM image shows. The SPR properties of gold nanoparticles can change when they are attached to another metal oxide like irion oxide. There are several papers on Au-Fe3O4 dumbbell particles and Au@Fe2O3 core@shell particles that show a shift in the UV-vis spectrum.

Considering the discussion it would be better, to compare the image with a positive control i.e. an ideal or earlier reported SPION-GOLD core-sheath particles and a negative control i.e. a SPION nanoparticle without the gold coating. Once you have these three images (-ve, +ve and test) you can conclusively point out and say which is which without any separation process involved.

Also, please see if by any chance would AFM or XPS be of use in this situation, since these can measure the percentage of Au and Fe for a given area of measurement.

You seem to be close to the solution, keep digging just a bit more.

Good luck

Separation of Fe3O4 core Au shell (if any) from only Fe3O4 and Au particles should be easy -- extract the particles in a long chain thiol / sonication / chloroform type system and let it pass through a magnetic filtration system -- a few iterations and you should have only core shell particles. UV-Vis is misleading until you actually have isolated the core-shell particles. HR EDAX imaging done in transmission should give you a good feel about the core shell nature of these particles. EELS of such core-shell is always difficult particularly because of the long collection time you need to get decent signal count from gold from small particles. But you can collect good EELS image of Fe3O4 particles -- and later dissolve the Fe3O4 cores in HCl and image the hollow shells using EELS, comparison of before and after images will give you a good sense of the composition. My random 2 cents!@!

Based on your TEM image I think that you can not conclude anything about core/shell, in fact the image shows that you have a misture between two types of nanoparticles. In some cases if you have overlap of nanoparticles of the same material you can get more dark regions that seems to be another type of nanoparticles. There are a very easy way to verify core/Shell nanoparticles, HR-TEM (high resolution-TEM). With this approach you are able to see if in fact you have core/shell, by mapping Au versus gold atoms and determination of diffraction pattern of diferent materials.

What I think?

If such a kind of TEM is available then can use higher voltage to 300 KV. It does not increase the temperature of specimen and almost works at room temperature. You should try to find core-shell Nanoparticles less than 100 nm in diameter or may be more smaller. Spread the e-beam over the whole area to have a good contrast image. Capture image in a short interval of time to minimize the e-beam effects on structural transformation of the specimen.

I hope this will work. Our group currently using Tecnai F-30 and usually we operate at 300 KV So, I can suggest you. Further you can use EDS or EELS for counter verifications.

STEM EDS mapping (bright and dark field) would help you a lot. Xu and Bhattacharyya, 2005, used that method. See screenshot attached where core and shell are shown as different colours- positively identifying them [(a) in the image]

See further here by the same authors in the same thesis