Research ArticleAPPLIED SCIENCES AND ENGINEERING

Quantizing single-molecule surface-enhanced Raman scattering with DNA origami metamolecules

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Science Advances  27 Sep 2019:
Vol. 5, no. 9, eaau4506
DOI: 10.1126/sciadv.aau4506
  • Fig. 1 Design principle and SEM characterization of super-origami DNA nanostructures with n-tuples.

    (A) Oligomeric super-origami templates for the construction of AuNP n-tuples. Arrows indicate the directions. (B) Atomic force microscope (AFM) characterization of DNA super-origami. (C to E) SEM characterizations of AuNPs n-tuples. Scale bars, 100 nm.

  • Fig. 2 Correlative SEM, DFM, and Raman characterization of tetrameric metamolecules.

    (A) Schematic illustration of the fabrication procedure. L-AuNPs (80 nm) and dyes could be immobilized site-specifically on a rhombus-shaped super-origami through DNA hybridizations. (B) FDTD calculations for an 80-nm L-AuNP tetramer cluster. A hot spot is present in the green box. (C to E) Correlative SEM characterization (C), DFM characterization (D), and Raman mapping (E) of an 80-nm L-AuNP tetramer cluster. Six ROX (carboxy-X-rhodamine) molecules were placed in the hot spot shown in (B). a.u., arbitrary units.

  • Fig. 3 DFM-SEM correlative characterization of the plasmonic properties of a tetrameric metamolecule.

    (A) Schematic of the DFM setup for measuring the scattering spectra of a single 80-nm L-AuNP tetrameric metamolecule. (B) Colocalized DFM and SEM images. Scale bars, 1 μm. (C and D) SEM image and scattering spectra (the experimental and theoretic) of the tetrameric metamolecule at different polarization angles of incident light. The orientation angles of the incident light relative to the cluster are shown in the middle column. (E) Theoretic extinction spectrum and surface charge distribution plot of the tetrameric metamolecule when the polarization angle of the incident light was 90°.

  • Fig. 4 Characterization and SERS spectra of tetrameric metamolecules.

    (A) Schematic of the tetrameric metamolecule that is incorporated with Raman dye. (B) Real-color photograph and the corresponding SEM images of the two individual tetramers (i and ii). Scale bars, 1 μm. (C) High-magnification SEM images reveal the difference between two tetramers. Scale bars, 100 nm. (D) FDTD calculations for two tetramer clusters. Scale bars, 50 nm. (E) Nonpolarized experimentally scattering spectra of the two individual tetramers. (F) Raman spectra of individual tetramers with intercalated SYBR Green I molecules (spectra i and ii) and the highly concentrated bulk solution (black curve) of SYBR Green I. All measurements were performed with a 633-nm excitation laser (10-s exposure).

  • Fig. 5 Quantized single-molecule SERS.

    (A) Schematic of the tetrameric metamolecules with accurate number of Raman dye ROX molecules in the hot spot. The diameter of ROX is ~1.6 nm, while the diameter of double-stranded DNA is 2 nm. (B) Schematic of the hot spot region with different numbers of ROX (N = 1, 2, 3, 4, 6, 9, 12). According to the calculated size of hot spot and the diameter of the ROX, six ROX can fill in the hot spot region. (C) SERS spectra taken from seven individual tetramers with different numbers of ROX. (D) Quantized SERS responses as measured by the intensity plot at 1504 cm−1 along with the increase of the number of ROX per particle (N = 12, red, 1 ROX; N = 14, orange, 2 ROX; N = 9, claybank, 3 ROX; N = 9, green, 4 ROX; N = 11, light blue, 6 ROX; N = 8, dark blue, 9 ROX; N = 8, purple, 12 ROX). (E) Measured EFs at 1504 cm−1. All measurements for EF calculations were performed with a 633-nm excitation laser (10-s exposure).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/9/eaau4506/DC1

    Fig. S1. Schematic drawings of DNA origami template.

    Fig. S2. Super-origami templates.

    Fig. S3. Characterization of 80-80 nm AuNP metamolecules.

    Fig. S4. SEM images of 50-80 nm and 80-80-80-80 nm AuNP metamolecules.

    Fig. S5. Schematic representation of SEM-DFM-Raman correlative imaging for plasmonic property investigations.

    Fig. S6. Characterization of the plasmonic properties of 80-nm homodimer [tuple (y, y)] using the “DFM-SEM correlative imaging.”

    Fig. S7. Characterization of the plasmonic properties of three metamolecules using the “DFM-SEM correlative imaging.”

    Fig. S8. The absolute scattering spectra of two homotetramers and two homotrimers.

    Fig. S9. FDTD calculations of the electromagnetic field (E) at mid-height of the tetrameric metamolecules.

    Fig. S10. SERS spectra taken from individual tetrameric metamolecules with different numbers of ROX.

    Supplementary Appendix

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Schematic drawings of DNA origami template.
    • Fig. S2. Super-origami templates.
    • Fig. S3. Characterization of 80-80 nm AuNP metamolecules.
    • Fig. S4. SEM images of 50-80 nm and 80-80-80-80 nm AuNP metamolecules.
    • Fig. S5. Schematic representation of SEM-DFM-Raman correlative imaging for plasmonic property investigations.
    • Fig. S6. Characterization of the plasmonic properties of 80-nm homodimer tuple (y, y) using the “DFM-SEM correlative imaging.”
    • Fig. S7. Characterization of the plasmonic properties of three metamolecules using the “DFM-SEM correlative imaging.”
    • Fig. S8. The absolute scattering spectra of two homotetramers and two homotrimers.
    • Fig. S9. FDTD calculations of the electromagnetic field (E) at mid-height of the tetrameric metamolecules.
    • Fig. S10. SERS spectra taken from individual tetrameric metamolecules with different numbers of ROX.
    • Supplementary Appendix

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