Mesostructured arrays of nanometer-spaced gold nanoparticles for ultrahigh number density of SERS hot spots

Ying Huang Lai, Shiaw Woei Chen, Michitoshi Hayashi, Ying Jen Shiu, Chiao Cheng Huang, Wei Tsung Chuang, Chun Jen Su, Hu Cin Jeng, Jhe Wei Chang, Yao Chang Lee, An Chung Su, Chung Yuan Mou, U. Ser Jeng

Research output: Contribution to journalArticlepeer-review

46 Citations (Scopus)

Abstract

A novel one-trough synthesis via an air-water interface is demonstrated to provide hexagonally packed arrays of densely spaced metallic nanoparticles (NPs). In the synthesis, a mesostructured polyoxometalate (POM)-silicatropic template (PSS) is first self-assembled at the air-water interface; upon UV irradiation, anion exchange cycles enable the free-floating PSS film to continuously uptake gold precursors from the solution subphase for diffusion-controlled and POM-site-directed photoreduction inside the silica channels. NPs ≈ 2 nm can hence be homogeneously formed inside the silica-surfactant channels until saturation. As revealed via X-ray diffraction, small-angle X-ray scattering (SAXS), grazing incidence SAXS, and transmission electron microscopy, the Au NPs directed by the PSS template are arrayed into a 2D hexagonal lattice with inter-channel spacing of 3.2 nm and a mean along-channel NP spacing of 2.8 nm. This corresponds to an ultra-high number density (≈1019 NPs cm-3) of narrowly spaced Au NPs in the Au-NP@PSS composite, leading to 3D densely deployed hot-spots along and across the mesostructured POM-silica channels for surface-enhanced Raman scattering (SERS). Consequently, the Au-NP@PSS composite exhibits prominent SERS with 4-mercaptobenzoic acid (4-MBA) adsorbed onto Au NPs. The best 4-MBA detection limit is 5 nm, with corresponding SERS enhancement factors above 108. Densely arrayed metallic nanoparticles are fabricated via self-assembly of a mesostructured polyoxometalate-silicate-surfactant (PSS) template at the air-water interface (left), followed by adsorption of metallic precursors to the PSS film via anion exchange (middle), then finished by polyoxometalate (POM)-site-directed photoreduction of the metallic anions and formation of metallic NPs inside the silicate-surfactant channels upon UV irradiation (right).

Original languageEnglish
Pages (from-to)2544-2552
Number of pages9
JournalAdvanced Functional Materials
Volume24
Issue number17
DOIs
Publication statusPublished - May 2 2014
Externally publishedYes

Keywords

  • arrayed nanoparticles
  • GISAXS
  • hot spots
  • mesostructures
  • SERS

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics

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