A systems approach towards the stoichiometry-controlled hetero-assembly of nanoparticles.

A central theme in nanotechnology is to advance the fundamental understanding of nanoscale component assembly, thereby allowing rational structural design that may lead to materials with novel properties and functions. Nanoparticles (NPs) are often regarded as 'artificial atoms', but their 'reactions' are not readily controllable. Here, we demonstrate a complete nanoreaction system whereby colloidal NPs are rationally assembled and purified. Two types of functionalized gold NPs (A and B) are bonded to give specific products AB, AB(2), AB(3) and AB(4). The stoichiometry control is realized by fine-tuning the charge repulsion among the B-NPs. The products are protected by a polymer, which allows their isolation in high purity. The integration of hetero-assembly, stoichiometry control, protection scheme and separation method may provide a scalable way to fabricate sophisticated nanostructures.