Gold Nanoparticle Synthesis: All About How To Do It

Gold (au) nanoparticles (aunps) are known to exhibit a combination of physical, chemical, optical and electronic properties. Gold nanoparticles play a multi-functional role. Hence Gold nanoparticle synthesis can be achieved by using various methods, majority of which follow the same rules that are applicable in preparation of other nanoparticles.

The five commonly used methods for gold nanoparticle synthesis are:

  • Turkevich method
  • Brust method
  • Perrault method
  • Martin method
  • Nanotech applications

Now let's look at these five ways in detail:

Gold nanoparticle synthesis using the Turkevich method

This method of gold nanoparticle synthesis was devised by someone known as J. Turkevich in the year 1951, and was later refined by G. Frens during the 70s. It is easily the simplest one of all gold nanoparticle synthesis methods.

It's primarily used for production of modestly mono disperse spherical gold nanoparticles (of around 10 nm to 20 nm diameter) suspended in water. It's possible to produce larger particles too, but not without compromising on the nanoparticles' shape and mono disparsity.

This method involves reaction of tiny amounts of hot H[AuCl4] or chloroauric acid with equally little amounts of Na3C6H5O7 or trisodium citrate solution. Such a reaction leads to creation of gold nanoparticles since the citrate ions function both as a capping and a reducing agent. Larger nanoparticles can be obtained by adding less of trisodium citrate, as less as 0.05%.

Gold nanoparticle synthesis using the Brust method

Another important gold nanoparticle synthesis method - this one was developed by Brust and Schiffrin during the early 90s. It's actively used for production of gold nanoparticles in the organic liquids, which aren't normally miscible (like toluene) with water.

In this method, H[AuCl4] or chloroauric acid solution is reacted with TOAB or tetraoctylammonium bromide solution. The reaction happens in sodium borohydride (NaBH4) and toluene, which function as a reducing agent and anticoagulant respectively.

The gold nanoparticles produced by this technique are 5 nm to 6 nm in diameter.

Perrault method of gold nanoparticle synthesis

An approach developed by Perrault and Chan in the year 2009, this method involves usage of hydroquinone for reduction of H[AuCl4] or chloroauric acid inside an aqua solution consisting of gold nanoparticle seeds (of 15 nm diameter).

This seed-based technique of gold nanoparticle synthesis is quite similar to the one used in case of photographic film development. The latter involves growth of silver grains inside the film, by introduction of reduced silver on its surface. In the same way, gold nanoparticles can act with the hydroquinone for catalysing the reduction of ionic gold on their surface.

The usage of a stabiliser like citrate helps in controlled deposition of the gold atoms on the nanoparticles.

Martin method of gold nanoparticle synthesis

A fairly simple method developed by Martin and Eah in the year 2010, it leads to generation of almost mono disperse gold nanoparticles in water.

This method involves careful control over the reduction stoichiometry, by making precise adjustments to the ratio of NaBH4-NaOH ions to the HAuCl4-HCl ions, in a manner that it's well inside the sweet zone. It, along with the heating provides reproducible diameter in the range of 3 nm and 6 nm.

The aqueous particles retain their colloidal stability owing to the high charge obtained from the excessive ions present in the solution. They can be further coated with several hydrophilic functionalities, or combined with hydrophobic molecules, in order to make them applicable in non-polar solvents.

Gold nanoparticle synthesis using nanotech applications

Bacterium like Bacillus licheniformis can also be used for gold nanoparticle synthesis. Researchers have successfully produced gold nanoparticles ranging between 10 nm-100 nm using this method. The particles are normally synthesised with the help of toxic reagents, in organic solvents.