I have made these 40 nm GNPs which I purified via dialysis until no traces of contaminants were detected by UV-vis. The GNPs do not aggregate over time (lambda max does not change, neither does the Z-average or PI) but they start losing the capacity of binding to antibodies and by week #2 the capacity has been reduced more than 50%. The nanoparticles are dialyzed against 0.01X PBS. If anyone could give me a hint towards what the issue might be I would greatly appreciate it
Hi Vivian Triana . What chemistry are you using to attach Ab's to the particles?
Steingrimur Stefansson I am only using passive adsorption, due to resource and time cost analysis, we want to avoid covalent strategies
Katja Werner I am using the hydroquinone assisted, Turkevich methodology (i.e. seed growth using hydroquinone as reducing agent and citrate as capping agent). Initially I thought benzoquinone was the culprit and tried to improve my purification method without success
Alan F Rawle We have not performed this analysis. Will suggest it
Thanks everyone for your responses and help
Vivian Triana
My thought is that the surface has oxidized and XPS should show this. We only ever found gold in the +3 oxidation state (and one could argue that you need an oxidized form to bond to negative capping agents). The surface is everything - composition, charge, corona, SSA etc. And for a system in air or water the the surface cannot be identical to the bulk.
Alan F Rawle thanks a lot for your insight! I will certainly ask for the analysis to be performed but in the meantime, and if I understand correctly what you mentioned about the oxidation state on the surface of the nanoparticles, I guess that maybe dialyzing against a buffer that has a small amount of reducing agent (mine currently is only 0.01X PBS) might help? During purification I was always afraid of removing citrate and thus reducing nanoparticle stability but I always thought that I should observe such stability changes via aggregation instead of via binding capacity. Will read more regarding the surface chemistry since I think the problem might be in the direction you are pointing. Thanks again
Vivian Triana
PBS is a phosphate (PO42-) buffer as you know, and imparts negative charge to the particle (as does the smallest citrate entity - the reducing agent in the Turkevich Au sol synthesis). The amount needed would be to just cover the surface (and a little more) and therefore is SSA dependent. Something related to this in (registration needed):
Dispersion and nanotechnology
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W190528DispNanoMat
Look at slide 32 in particular but anything from slide 18 may be of interest. The following may also be entertaining:
Metal colloids - their preparation, application and characterization
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W160218MetalColloids.html
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