Multivalent assembly of ultrasmall nanoparticles: One-, two-, and three-dimensional architectures of 2 nm gold nanoparticles

The assembly of nanoparticles (NPs) into complex structures is a fundamental topic in nanochemistry. Although progress has been made in this respect, the classical treatment of NPs as hard building blocks that lack the ability to anisotropically “bond” to each other limits the construction of more complex assemblies. More importantly, extension of methods of assembly of robust NPs to the assembly of ultrasmall ones with size below 2 nm is still challenging. Here we report the controlled self-assembly of ∼2 nm gold NPs into one-dimensional (1D) nanochain, two-dimensional (2D) nanobelt and three-dimensional (3D) nanocomet architectures by kinetically controlling the diffusion of ultrasmall gold NPs with anisotropic surfaces in solution. This process is presumed to allow selective ligand exchange with linkers at different binding sites on the NP surface, and results in “multivalent” interactions between NPs. Different from the assembly of “hard building blocks”, our results demonstrate the significance of surface effects for ultrasmall NPs (or clusters) in determining the structure of complex self-assemblies, and suggest the possibility of assembling these “molecule-like” ultrasmall nanocrystals into novel complex materials on a nanoscale approaching that of real atoms or molecules.