Hollow and inward-bumpy gold nanoshells fabricated using expanded silica mesopores as templates

Plasmonic nanoparticles can produce an enhanced electromagnetic field in their vicinity due to their localized surface plasmon resonance (LSPR). In particular, gold nanoshells (NSs) are of great interest due to their tunable LSPR absorption band ranging from the visible to the infrared region with superior bio-compatibility. We have fabricated hollow and bumpy Au (HBA) NSs with rough surfaces using expanded silica mesopores as templates. Because some Au seeds were located at the inner surfaces of silica mesopores, the produced Au NSs have inherent inward-grown nanobumps. During seven successive reduction steps, the LSPR peak of Au nanostructures shifted progressively toward a longer wavelength as the sizes of Au seeds increased gradually. Measuring the cross-sections of HBA NSs milled by a focused ion beam, we have found that hollow and bumpy nanostructures arose from the pore structures of mSiO(2) nanotemplates. HBA NSs confine Raman-probe molecules well owing to their hollow structures and have ragged surfaces due to their inward-bumpy morphologies, exhibiting highly efficient surface-enhanced Raman scattering activity.