Standard methods typically produce nanoparticles about 1 OD in concentration but just increasing the reactant concentration several fold doesn't produce the desired products
With Citrate as reducing agent, the maximum concentration of chloroauric acid you can reduce is 0.01wt% but if you are using strong reducing agent like NaBH4, you need to optimize the protocol for certain size and best part about the protocol is that the synthesis is below room temperature and you can reduce high concentration chloroauric acid with tri-sodium citrate as stabilizing agent.
One convenient method that is most often used for preparing Au NP solutions of a very specific concentration is to use centrifugation to concentrate Au NPs. This can be done to give Au NP solutions with up to 10 - 20 x the OD of the original solution. Au NPs with diameters of larger than 8 - 10 nms can typically be brought down in water by centrifugation at 9,000 - 15,000 RCF (most centrifuges provide a relationship between rpm and RCF in the manual) to form a pellet at the bottom of the centrifuge tube. This pellet can then be redispersed by sonication into fresh water to prepare a concentrated solution. Smaller particles or those that have very stable interactions with the solvent may require more rigorous centrifugation.
It is important to note that centrifugation can result in aggregation of the particles but the centrifugation time and RCF can be optimized to minimize the aggregration.
Thanks Christopher. I have tried centrifugation and whilst it works there is a high loss from aggregation. I'm looking for a chemical method for simplicity.
If you know your initial concentration, we have also evaporated the solvent to create a concentrate. This will only work with strongly capped particle since heat can desorb the capping ligand and cause aggregation.
With Citrate as reducing agent, the maximum concentration of chloroauric acid you can reduce is 0.01wt% but if you are using strong reducing agent like NaBH4, you need to optimize the protocol for certain size and best part about the protocol is that the synthesis is below room temperature and you can reduce high concentration chloroauric acid with tri-sodium citrate as stabilizing agent.
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