In 2006 our group published a JACS communication (J. Am. Chem. Soc. 2006, 128, 15980) that represented a paradigm change in the way in which unprotected nanoparticles can be prepared in just a few minutes and at room temperature. The reaction takes advantage of the strong electron donating properties of ketyl radicals to reduce Au(III) to Au(0) in solution; the latter spontaneously makes gold nanoparticles (AuNP).
Since our initial discovery in 2006 our work has covered many metals and applications, for example, silver nanoparticles (AgNP) can be made with controlled size and morphology by irradiating small AgNP with light of different colours, conveniently supplied by inexpensive LED (J. Am .Chem. Soc. 2010, 132, 1825). The picture below shows a rainbow of colours obtained by this methodology.