The Brust-Shriffin method is the standard for producing ultrafine gold nanoparticles (or arguably clusters at that scale) down to ~1nm in diameter. They tend to be stabilised with alkanethiols, with strong Au-S bonds and long non-polar, hydrophobic tails. No other synthesis method to my knowledge (Turkevich, Frens, Duff etc) can reliably get down to that size.
For my application, I need ~1 nm (not 2 nm) GNPs that are soluble in water, so the stabilising agent needs to have an amine, hydroxyl or carboxyl group etc.
I see three options:
1) Brust-Shriffin, then ligand exchange, although I can't find any literature going from thiol to a less stable polar ligand, only the other way around. Also aggregation issues.
2) Use an untested thiol with a polar group on the other end of the chain.
3) A synthesis method I have not come across, perhaps adding a second reducing agent (tannic acid, glutathione) to a Turkevich (citrate) synthesis.
Any suggestions would be very much appreciated, thank you!
You write, "which are soluble in water." This is your mistake or you need to dissolve the gold nanoparticles in water. Various thiols really stabilize gold nanoparticles. If gold nanoparticles dissolve, then gold in water will be in the form of ions.
Yuri, Alan and Baraa,
I apologise, I should have been clearer. I am looking for ~1 nm diameter gold nanoparticles, which when stabilised, are water soluble. For example, sodium citrate stablised gold nanoparticles which are commercially available in water. There is a method which produces citrate stabilised 2 nm GNPs using a stronger reducing agent, but not as low as 1 nm. Gold metal is, as you correctly say, completely insoluble in water.
Hi Finlay Apologies for the pedantic nature of the initial response but care in defining the issue is key. Again you’re wanting, as I suspect, to disperse or produce a 1 nm stabilized Au colloid in an appropriate continuous phase. The concept of solubility (one phase) does not apply to a 2-phase system (solid in liquid). A couple of calculations for you to do. What is the size of an Au atom? How many could you confine in a 1 nm particle? How much extra in size would the protective layer add? Note that the volume or mass of a 1 nm particle is 1/8th of a 2 nm particle.
Thank you all again for your detailed responses. Paolo Passaretti you've essentially provided the answer - I will be making clusters of 25 gold atoms which are protected by l-glutathione, which is full of polar functional groups, making the particles water soluble. The 13 atom icosahedral core is ~1 nm and the surrounding Au/S layer makes them 2 nm overall, exactly what I need. I will use the method here: Article Atomically Precise Au 25 (SG) 18 Nanoclusters: Rapid Single-...
That sounds great! I am glad my reply helped you to find a solution :)
I wish you all the best with your research!
You should try PEG-SH (with average Mw about 400) as stabilizer agent.
Finlay Walton
Sorry I'm late to the discussion. You write on June 28: 'making the particles water soluble'. Just reread this.
No, you still have a 2-phase system (particles in continuous phase), so things like light scattering and Brownian motion will take place. If it was a true solution then the system would be completely dissociated and only a single phase would be present. It would be pure continuous phase. There would be no light scattering phenomenon in such a system and you would not be able to carry out characterization experiments as there would be no heterogeneity/interfaces in such a system.