Templated synthesis of gold nanorods (NRs): The effects of cosurfactants and electrolytes on the shape and optical properties

Seeded growth of gold nanorods (NRs) has been accomplished in a micellar medium containing mixed surfactants or a high salt concentration. Cetyl trimethylamoniumbromide (CTAB) forms micelles upon which the growth of rod shaped gold nanoparticles occurs. AgNO3 is introduced into the growth solution to enhance the formation of NRs. The roles of non-ionic surfactants such as Tween and Triton, and of electrolytes such as sodium chloride and potassium chloride have been examined. As the concentration of these additives in the growth solution is increased, the aspect ratio of the NRs increases to a critical limit, after which it decreases again. Upon carefully controlling the content of Triton X-100 or Tween 20 in the growth solution, these nonionic surfactants assisted in fine-tuning the shape of gold NRs (e.g. rectangular or dogbone). The growth pattern of the NRs fits into the model of a soft template formed by the mixture of CTAB and non-ionic surfactants.