Colloidal, hybrid nanoparticles are single particles comprising several active domains, for example, of metallic, semiconducting, or magnetic materials, and have potential applications in a wide variety of fields including solar energy conversion, catalysis, medical therapies, and electronics. The domain boundaries allow for direct electronic and magnetic communication between the component materials, and this intimate contact and selective arrangement of domains provides a unique pathway to tuning the particle properties. Predictive and controlled arrangement of these domains is clearly a nontrivial challenge. However, M.R. Buck, J.F. Bondi, and R.E. Schaak from the Pennsylvania State University have recently reported a stepwise and robust synthetic approach for generating complex hybrid nanoparticle structures, as published in the November 13, 2011 online edition of Nature Chemistry (DOI: 10.1038/NCHEM.1195).

The researchers first generate a class of metal-Pt-Fe₃O₄ heterotrimers. Stepwise thermal decomposition of Fe(CO)₅ in the presence of Pt seed particles generates Pt-Fe₃O₄ dimers, and subsequent reduction of a chosen metal precursor (for Au, Ag, Ni, or Pd) in the presence of these dimers then results in a high yield of heterotrimer structures. Surprisingly, each reduction reaction resulted in heterogeneous nucleation of the Au, Ag, Ni, or Pd exclusively on the Pt domain of the Pt-Fe₃O₄ dimers. This occurs as direct contact between the Pt and Fe₃O₄ domains facilitates electron transfer to the Pt domain, leading to the observed chemoselective deposition of the metal at the Pt surface.

Heterotetrameric particles were also synthesized by depositing Cu_xS or PbS domains on Au-Pt-Fe₃O₄ heterotrimer seeds. Again, while many products would appear to be possible, in both cases the new domain was located exclusively on the Au domain. It was suggested that while sulfur adsorbs to all domains of the heterotrimer, it was selectively localized on the Au due to differences in the rate of sulfur adsorption and reaction with Cu⁺ ions at the Au versus Pt surfaces. The Au-Pt-Fe₃O₄ heterotrimers were also used to generate higher order oligomers of 2–5 trimers by heating them in the presence of sulfur.

Through this study, the researchers demonstrated that a sequential reaction approach can provide a powerful route to the synthesis of complex hybrid nanoparticles. In combination with existing mechanistic understanding of the reactions involved, this strategy can lead to the rational synthesis of larger multidomain hybrid nanoparticles with increasing architectural complexities.