I am currently working on synthesizing some spiky gold nanoparticles and I have closely followed the protocol in “Realizing a Record Photothermal Conversion Efficiency of Spiky Gold Nanoparticles in the Second Near-Infrared Window by Structure-Based Rational Design” paper but I have not been successful at achieving a spiky structure using gold nanorods seeds of similar size as mentioned in the paper.
Here are my main questions:
On the gold nanorod seeds:
- The paper states “The resulting Au NRs were concentrated 8 times, dispersed in the CTAB solution for further use”. Then “As-prepared Au NRs (1 mL) were stirred with glutathione (GSH; 0.01M, 360 μL) for 2 h to form GSH-functionalized Au NRs before use” Are the AuNRs seeds washed to remove CTAB surfactant before stirring with GSH or at this point the CTAB-suspended AuNRs are directly used as it to mix with GSH?
On the spiky gold nanoparticles
- “After further stirring for 5 min, the flask was transferred to a water bath at 28 °C and left undisturbed overnight, yielding spiky Au6 NPs with good reproducibility” What is the color change observed at this step please? Dark grey/green-ish color? My samples change closer to a light purple which does not go along with the expected.
I have tried both the standard and optimal conditions and amounts of the reagents as indicated in the paper but I am still not observing the red shift (in the uv-vis measurments) nor spiky morphology.
Dear Cynthia Sangang many thanks for your very interesting technical question. As an organometallic chemist I'm certainly not a proven expert regarding nanoparticles, so for me it's very difficult to give you a qualified answer. The synthetic method is rather sophisticated, so it is certainly advisable (as suggested by Riaz A. Khan) to strictly adhere to the description. However, in my personal experience not every synthetic procedure is designed to be easily reproducible...😎
Particularly the phrase "The resulting Au NRs were concentrated 8 times (??), dispersed in the CTAB solution for further use" is not really clear to me. Apparently the Au NRs are first washed with water and isolated by centrifugation and then re-dispersed in CTAB solution. As the amounts of material are very small in these preparations, you could try a series of experiments in which you either remove the CTAB surfactant by washing or leave it in the solution.
As for the color, I assume that a purple color indicates the presence of "normal" gold nanoparticles. In this context please have a look at the following useful article in which an alternative preparation of spiky gold nanoparticles is described:
Adjuvant-Loaded Spiky Gold Nanoparticles for Activation of Innate Immune Cells
Article Adjuvant-Loaded Spiky Gold Nanoparticles for Activation of I...
This article is freely available as public full text on RG and can be downloaded as pdf file. In this study the authors that the spiky gold nanoparticles (SPNGs) exhibit a "greenish-black" color.
Other potentially helpful references can be found and accessed by searching the "Publications" section of RG for the term "spiky gold nanoparticles":
https://www.researchgate.net/search.Search.html?type=researcher&query=spiky%20gold%20nanoparticles
I hope this helps. Good luck with your research and best wishes, Frank Edelmann
Frank T. Edelmann Thanks for this answer professor!
I also found the "concentrated 8 times" quite subjective even though it is a critical step in the synthesis so in my experiments I simply varied just how concentrated those seeds were by adjusting the amount of CTAB/DIW I resuspended the AuNRs in.
As for the color, I had originally thought the end product should be of dark gray/green-ish color (from other literature) but I reached out to the authors of this paper and one of them just informed me that their end product is of blue/purple color which is what I obtained however my SPR peak (uv-vis) seems to be different than theirs. So I'll have to investigate why.
I also plan on doing TEM this week to confirm morphology so hopefully my new samples actually show spiky structure albeit of different size than the original.
The "Adjuvant-Loaded Spiky Gold Nanoparticles..." is actually the second method I was already considering after this one.
Thanks for your input!
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