Constructing The Gilded Cage

More robust metal nanocages, with potential catalysis and biomedical applications, are on the horizon, thanks to a new nanoconstruction procedure (Angew. Chem. Int. Ed. 2006, 45, 8126). Most methods for making metal nanocages produce structures composed largely of discrete nanoparticles, which tend to be unstable.

Using a liposome as scaffolding, John A. Shelnutt and coworkers at Sandia National Laboratories, Albuquerque, N.M., were able to assemble nanocages that survive for at least a year at ambient conditions and can stand up to mild sonication. The key to the nanocages' stability is that they're composed of branched platinum structures rather than existing as individual solid nanoparticles.

Shelnutt's group creates this dendritic structure by loading the liposome's bilayer with a porphyrin photocatalyst. When irradiated with white light in a platinum salt solution, the photocatalyst reduces the platinum into metal seed particles within the liposome. Once the seeds reach a certain size, their growth becomes autocatalytic, and their dendritic growth continues until the platinum salt is used up.