Quick Review of nanometals
Nanometal (also called metal nanoparticles) is very attractive and that is because of their size and shape dependent properties. The optical properties (linear and nonlinear) depend on that and they on dominated by something called the collective oscillation of conduction electrons. There are so many ways that you can prepare metal nanoparticles but the most used methods are based on wet chemistry. You can find nanometal being used in medical applications to the weaponry the military use. Nanometals also have a thing called Surface Plasmon Resonance (SPR) this is what cause the change in colors that we see. For example in the 4th century when the Lycurgus cup was created. The cup changes red when the light is shone inside of the cup and green when reflective light is shone on the outside of it. There are so many methods that you can prepare nanometals and the most popular way is by reducing HAuCl4 (chlorauric acid) in a sodium citrate solution that is boiling and then the formation of gold nanoparticles are revealed by a deep red color that looks like wine in about 10 min.
Types of nano metal synthesis
The most common types of nano metal synthesis deal with 'wet' methods in which metal nano particles are produced in a colloid with an organic material of some sort.
Gold nano particles can be produced by either:
1) Reduction of HAuCl4 in a solution of sodium nitrate, then boiling it, causing gold nano particles to form in a wine-red solution.
2) Mixing HAuCl4 in water, which produces a solution that is subsequently transferred into toluene using tetraoctylammonium bromide (TOAB), a phase transfer catalyst. Phase transfer catalysts help reactants dissolve in organic (carbon-containing) material where the reactant otherwise couldn't w/o the PTC. Afterwards, the solution is stirred with sodium borohydride, in the presence of certain alkanes, which bind to the gold in the solution, allowing for the formation of gold nano particles.
Synthesis of other metal nano particles can possibly be achieved by reducing metal salts in organic solvents such as ethanol, or by variations of the above methods which synthesize gold nano particles.  
- Luis M Liz-Marzán. "Nanometals formation and color", Materials Today, February 2004, page 27.
- Phase transfer catalyst-Wikipedia. http://en.wikipedia.org/wiki/Phase_transfer_catalyst