I have synthesized silver nanoparticles that were capped/functionalized by cysteine molecule. Can we confirm the cysteine capping by TEM analysis by comparing the TEM images of uncapped nanaoparticles and cysteine capped nanoparticles? Can a cysteine layer be easily seen under transmission electron microscopy (TEM)?
To the best of my knowledge, it is not possible to see cysteine or its layer on/around silver nanoparticles using TEM. However, Energy dispersive X-ray analysis that can be performed with the harware attached with TEM (or even SEM) can help in identifying elements attached with silver nanoparticles. Presence of S and N will give an indirect idea regarding the association of cysteine along with silver nanoparticles.
Hello, Verna,
I think a cysteine layer isn´t enough electrodense to be detected by a TEM, to be seen as dark dots in the image. However, if you have an coupled EDS in the TEM (and usually there is) you could look for S signals in the image. So, you would not have a direct evidence of the layer, but if you have S in your nanoparticles, it is an indirect evidence.
Best regards,
JP
Here's how I would go about imaging this. First, it is good that you want to prepare a control sample. Prepare the starting Ag-NP material on lacey-carbon films. Image the Ag-NPs that lie over the holes in the lacey grid. If the Ag-NPs do not have a significant amorphous layer around them, then you can proceed to looking at the cysteine-capped Ag-NPs. If they do, then you need to find out what is contaminating them. They may be contaminated before you prepare them for TEM. Once you can image clean Ag-NPs, get images and baseline EDX spectra. Then prepare the cysteine Ag-NP material in the identical way as the clean prep. You should be able to see an increase in amorphous material on the perimeter of the Ag-NPs that are over the holes in the lacey-C ("in vacuum"). The S in cysteine may be able to be detected by EDX, but there are many pitfalls to this. So, if you find S in the cysteine-capped sample and not in the control, then you have proven that cysteine is there. If not, it still is probably cysteine-capped, but EDX is not able to detect S. However, look for S on the lacey-C film also. Sometimes I have found S on the amorphous C support film where there is no sample. If this is the case, and S was not detected on the control lacey-C film, the S was probably in the suspension solution and now confounds your conclusions!
Try to think of any way that your analyses could be wrong and devise a test to determine
Good luck,
Ken
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