Past, present, and future of gold nanoparticles.

Colloidal gold nanoparticles have been around for centuries. Historically, the use of gold nanoparticles has been predominantly found in the work of artists and craftsman because of their vivid visible colors. However, through research, the size, shape, surface chemistry, and optical properties of gold nanoparticles are all parameters which are under control and has opened the doors to some very unique and exciting capabilities. The purpose of this chapter is to review some of the important discoveries and give background in regard to gold nanoparticles. First, the most common wet chemical methods toward their synthesis are reviewed, specifically discussing routes toward spherical colloidal synthesis and controllable rod formation. Next, because many applications of gold nanoparticles are a result of their magnificent interactions with light, some of the basic optical-electronic properties and the physics behind them are elucidated. Finally, by taking advantage of the optical-electronic properties, numerous proven applications for gold nanoparticles are discussed, as well as their predicted applications in the future.