© 2007 Nature Publishing Group ARTICLES Self-assembly of metal–polymer analogues of amphiphilic triblock copolymers

Organized arrays of anisotropic nanoparticles show electronic and optical properties that originate from the coupling of shape-dependent properties of the individual nanorods. The organization of nanorods in a controllable and predictable way provides a route to the fabrication of new materials and functional devices. So far, significant progress has been achieved in the self-assembly of nanorod arrays, yet the realization of a range of different structures requires changing the surface chemistry of the nanoparticles. We organized metal nanorods in structures with varying geometries by using a striking analogy between amphiphilic ABA triblock copolymers and the hydrophilic nanorods tethered with hydrophobic polymer chains at both ends. The self-assembly was tuneable and reversible and it was achieved solely by changing the solvent quality for the constituent blocks. This approach provides a new route to the organization of anisotropic nanoparticles by using the strategies that are established for the self-assembly of block copolymers. One-dimensional nanoparticles have a range of shape-dependent properties, for example, absorption, photoluminescence, surface-enhanced Raman cross-sections and conductivity1–4. These properties determine potential applications of discrete anisotropic nanostructures in optical and electronic devices1–3,5,6, sensing and imaging7,8, biodiagnostics8 and drug and gene delivery9,10. Self-assembly or assisted assembly of nanorods into organize