New types of nanomaterials: powders of gold nanospheres, nanorods, nanostars, and gold-silver nanocages

We describe a new strategy for the fabrication of plasmonic nanopowders (dried gold or composite nanoparticles) by using wet chemical nanoparticle synthesis, PEG-SH functionalization, and freeze drying. This strategy is illustrated by the successful production of four plasmonic nanopowders, including gold nanorods, nanostars, gold-silver nanocages, and gold nanospheres. The dried nanoparticles can be stored for a long time under ordinary conditions and then easily dissolved in water at a desired concentration without heating, intense sonication, or other harsh treatments. According to the MTT assay with SPEV-2 cells, gold nanorod powder is not toxic at concentrations up to 100 mg/L. Redispersed samples maintain the plasmonresonant properties of the parent colloids and do not form aggregates. These properties make pegylated freeze-dried gold nanoparticles (GNPs) applicable in various fields of biomedicine.