Small hairy balls

Stable gold nanoparticles consist of a mere handful of gold atoms -- typically about one hundred. These "balls" of atoms are covered in organic molecule ligands (the "hair") which prevent the gold atoms from sticking to each other and forming crystals. These molecular hairs are crucial to the various possible uses of the nanoparticles (catalysts, sensors, drug delivery, contrast agents and more) as the surface chemistry is largely controlled by what kind of "hair" is attached. It turns out that another important aspect of developing these particles is understanding how different types of ligands exchange on the surface of these particles. Hairy-gold-nanoparticle pioneer Hannu Häkkinen explains "when ligand exchange reactions are better understood, we hope to fully control the surface functionalization of the Au102 and similar water-soluble gold nanoparticles. The implications in biology for a fully controllable synthetic surface the size of a protein are profound."