Hi, I'm making 40nm colloidal gold and following the protocol I always use but now everytime I do it a thin solid film of gold appears on top of the colution and even if I remove it via filtration the gold is in bad shape and small granules appear the next day, any ideas to fix this?
I use citrate as a reducing agent
Héctor Osorio-Vega
Looks like your chemicals and concentrations are having the gold equivalent of the silver mirror test. See slide 28 in:
Silver colloids and invisible ink
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W150902SilverColloidInvisibleInk.html
Thank you I saw the video but the effect is not really the same, It did give me the idea that it might be gold reagent that has become damaged over time, however, I'll keep trying to find other alternatives.
I would describe the solid in the colloidal gold solution like they look like when you add starch to water, the solid floats on top of the solution and slowly becomes a layer that covers a good portion of the surface. I'll try to get a picture. The color of the solid is grey or grey-purple
Have you checked for possible contamination in your liquid host or even in the cuvette surfaces (e.g., residues after a previous cleaning) ? An impurity causing gold particles aggregation could be present, or a more intriguing explaination is the formation of more or less extended islands of some light polymer decorated with gold particles, which could justify the occurrence of a supernatant.
May I suggest you to analyze the chemical quality of each individual ingredient, starting from the host (water, I guess), and also of the supernatant?
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