Controlled step growth of molecularly linked gold nanoparticles: from metallic monomers to dimers to polymeric nanoparticle chains.

The solution-phase assembly of 15 nm gold particles into relatively linear chains of fairly controllable length of up to 1 mum is achieved by molecularly linking nanoparticles with alkanedithiols. This step-growth process can be controlled to prepare dimers, oligomers, and polymer-like gold nanoparticle chains by varying the ratio of alkanedithiols to nanoparticles. These size-controlled, relatively linear aggregates remain suspended in ethanol solution without precipitation for several weeks to months depending on the chain length. The resulting soluble nanoparticle assemblies were characterized by a variety of techniques including cryogenic transmission electron microscopy. The surface plasmon coupling of regularly spaced gold nanoparticles in these chains could be of interest in the fabrication of optical waveguide and nanoelectronic systems.