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A general approach involved template-engaged displacement reaction has been demonstrated to prepare metal nanostructures with hollow interiors by reacting solutions of appropriate salts with solid metal nanostructures. For example, silver nanostructures with various morphologies including triangular plates, cubes, spheres, rods and wires have been used as templates to react with an aqueous chloroauric acid solution. The reaction led to the formation of hollow nanostructures with shapes similar to that of silver templates. The void space, wall thickness, and crystalline structure of these hollow structures were determined with the silver templates, which were converted into soluble species during the displacement reaction. Elemental analysis and electron microscopic studies indicated that these hollow structures were made of gold/silver alloys. The capability and feasibility of this method have also been demonstrated by preparing nanotubes made of different metals (e.g., gold/silver, palladium/silver, and platinum/silver alloys). The hollow nanostructures of gold/silver alloys exhibited significantly different surface plasmonic properties from their solid counterparts. For instance, the extinction peaks of the nanoshells of gold/silver alloy with roughly spherical shape were considerably red-shifted as compared to solid colloids of silver or gold having approximately the same dimensions. The high extinction coefficient in the red and near infrared regimes should make these nanoshells particularly useful as components in fabricating plasmonic devices and labels in probing the desired biomolecules.
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