Hi!
I prepared AuNPs using the citrate method and tried purifying them. I aliquoted the resulted AuNP solution in 2 mL volumes and centrifuged at 6000 rpm for 1 hr at 4 celcius as the first purification step to obtain a AuNP pellet. However, I found the nps agglomerated at the bottom of the tube as a dark precipitate. Some tubes showed a grayish blue solution after centrifugation.
I followed the same method and chemicals I used for a previous synthesis where I could successfuly obtain nanoparticles without agglomeation. But, that time I did the centrifugation at 25 celcius. The method has not given a specific cetrifugation temperature, I used 4 celcius as I thought it may support better stability for the AuNPS. Both times I prepared the solutions in millipore water (deionized).
I'm glad if someone can provide a possible explanation for my observation. Can it be due to the centrifugation temperature used (4 celcius) after preparing the nanoparticles in boiling temperature? I'm new to this field and thanks in advance..
Herewith I'm attaching some pics
Yes, the temperature would be a factor. You can repeat the process with the temperature you did earlier.
You should centrifuge as few times as possible and for as short a time as possible, as aggregation is always a risk. The different colors just signify differing degrees of aggregation, and it will irreversible for all the colors in the images.
Personally, I would not use de-ionized water (which I think you have used for the wash steps) as you will remove the citrate. The citrate stabilizes the particles, and I would wash with weak citrate buffer.
Even then, be as gentle as possible in the centrifugation steps. Particles will also stick to certain surfaces and you may need to experiment with different tubes/plastics.
@Nick Gee
Thank you very much. I also used 0.5mM citrate buffer for the washing step. These images are taken after the 1st centrifugation step, when I centrifuged the AuNP solution prepared to obtain a pellet.
Thank you sir..I didn't do a wavelength scan prior to centrifugation. All colour changes in the synthesis process were normal and I obtained a wine red solution at the end.I'm going to repeat it with different tubes and centrifugation at 25 celcius. Again thanks for your concern..😊
@ Nick Gee
I did the nanoparticles synthesis again. I did the centrifugation at 25 celcius and 7000 rpm for 45 mins. I could obtain a nice AuNP pellet without agglomeration.
Therefore, the centrifugation temperature has caused the problem.
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