Gold nanorods:: Synthesis, characterization and applications

This article provides an overview of current research into the synthesis and properties of gold nanorods. Interest in rod-shaped nanoparticles stems from their unique optical properties, which can be approximated by Mie-Gans theory. We begin by outlining briefly the origin of the shape-dependent optical properties of rods. The different synthetic strategies that have been developed to achieve decent yields and sample monodispersity are then described, and the methods used for physical characterization as well as results of inorganic structure studies follow. Some of the most innovative research dealing with surface modification and chemical reactivity of gold nanorods is highlighted, together with new directions such as the synthesis of core-shell particles and the interactions of gold nanorods with biomolecules. Gold nanorods can be excited by ultrafast laser-induced heating; the resulting relaxation processes are important in determining the material properties of the metal particles. In addition, vibrational modes and shape changes are elucidated, and a theoretical analysis of the expected behavior is also presented. The incorporation of the gold nanorods into thin films and gels provides a new avenue for designing and growing materials with anisotropic optical properties. Initial results on the optical properties of such nanocomposites are reviewed. This review is concluded with a section devoted to the future perspectives for gold rods as novel materials. (c) 2005 Elsevier B.V. All rights reserved.