Surface-enhanced Raman scattering activities of gold nanocap arrays and hollow gold nanocap particles

Gold (Au) nanocap arrays and hollow gold nanocap particles were prepared by dip-coating technique combined with wet chemical reduction method, and followed by sonication and dissolution of the silica colloidal template. The surface morphologies and optical properties of the obtained samples were characterized by scanning electron microscopy, transmission electron microscope, and ultraviolet-visible spectrophotometer, respectively. Gold nanocap arrays and hollow gold nanocap particles were used as substrates to detect the surface-enhanced Raman scattering spectra of malachite green and methylene blue (MB), respectively. It was found that the gold nanocap arrays had higher enhancement ability than hollow gold nanocap particles, with enhancement factor of 1.3 x 10(5) and 3.5 x 10(3), respectively. In addition, gold nanocap arrays exhibited excellent reproducibility with a relative standard deviation of less than 5% and about 10% across a single substrate and between different substrates, respectively. The minimum detection limit for MB adsorbed on hollow gold nanocap particles was down to 0.01 mu M.