A team of scientists, working in part at SSRL's crystallography beam lines and led by Stanford Professor Roger Kornberg, has determined for the first time the atomic structure (at 1.1 Å resolution) of a thiol-covered gold nanoparticle, a discovery with potential for a range of applications from biosensors to nanotransistors. The results are published in the October 19 issue of Science.

Gold is an appealing metal for many uses because of its softness, optical and electrical properties, and because it does not oxidize. However, a plain gold surface may not be compatible with certain applications, so scientists are experimenting with gold clusters and surfaces coated with organic molecules, such as thiols. The organic layer, which self-assembles in a geometric array on the gold surface, changes the gold's chemistry. For example, coating gold can make it biocompatible for implantation into living organisms. Another possible application is to make self-lubricating materials.

Synthesizing well-defined thiol-coated gold nanoclusters is a challenging process. This thiol-coated structure, confirmed from the screening of 15 separate crystals derived from multiple preparations, shows homogeneous clusters of 102 gold atoms surrounded by 44 molecules of p-mercaptobenzoic acid. The central gold atoms are packed with decahedral symmetry, with additional layers of gold atoms in unexpected geometries. The cluster is coated by a thiol monolayer, with each sulfur bridging between two gold atoms, and with stabilization of the coat provided through several types of interactions between the thiol molecules. This structure will assist in the understanding of principles of nano-core assembly and the theoretical basis of gold-thiol interactions.

P. D. Jadzinsky, G. Calero, C. J. Ackerson, D. A. Bushnell and R. D. Kornberg, "Structure of a Thiol Monolayer-Protected Gold Nanoparticle at 1.1 Å Resolution", Science 318, 430 (2007)

To learn more about this research see the full scientific highlight at:
http://www- ssrl.slac.stanford.edu/research/highlights_archive/goldnano.html