Self-assembly of nanoparticles into structured spherical and network aggregates

Multi-scale ordering of materials is central for the application of molecul ar systems(1-3) in macroscopic devices(4,5). Self-assembly based on selecti ve control of non-covalent interactions(6-8) provides a powerful tool for t he creation of structured systems at a molecular level, and application of this methodology to macromolecular systems provides a means for extending s uch structures to macroscopic length scale(9-11). Monolayer-functionalized nanoparticles can be made with a wide variety of metallic and nonmetallic c ores, providing a versatile building block for such approaches. Here we pre sent a polymer-mediated 'bricks and mortar' strategy for the ordering of na noparticles into structured assemblies. This methodology allows monolayer-p rotected gold particles to self-assemble into structured aggregates while t hermally controlling their size and morphology. Using 2-nm gold particles a s building blocks, we show that spherical aggregates of size 97 +/- 17 nm c an be produced at 23 degrees C, and that 0.5-1 mu m spherical assemblies wi th (5-40) x 10(5) individual subunits form at -20 degrees C. Intriguingly, extended networks of similar to 50-nm subunits are formed at 10 degrees C, illustrating the potential of our approach for the formation of diverse str uctural motifs such as wires and rods. These findings demonstrate that the assembly process provides control over the resulting aggregates, while the modularity of the 'bricks and mortar' approach allows combinatorial control over the constituents, providing a versatile route to new materials system s.