Credit: © 2009 ACS

Nanoparticles can be tailored for any number of applications, because their properties depend on their shape and size as well as their chemical composition. To achieve this goal, it is useful to catalogue the 'family trees' of particles that can be obtained from just one reaction. Jiaxing Huang and co-workers at Northwestern University, Illinois and California State University have constructed the first evolutionary tree describing a large family of gold nanoparticles, all of which have unique optical properties1.

The researchers chose gold nanorods as the 'seed' material, or ancestor, of their family tree. They identified three main evolutionary pathways that the nanoparticle can follow, using growth solutions of slightly different concentration and pH. The three pathways produce particles shaped like peanuts, square cuboids or octahedrons, and different sizes can be isolated by interrupting each pathway at different stages of development.

The researchers acquired even more types of nanoparticle by cross-breeding across evolutionary pathways. For example, by placing square cuboids in the growth solution for octahedrons, they produced elongated octahedrons.

This three-branch tree probably represents only a small portion of all the particles that can be produced from gold nanorods. By completing the family trees for this and other systems, researchers could more easily develop specific nanoparticles for applications such as biological labelling, sensing or drug delivery.