Metal nanoparticles have unique optical properties such as localized surface plasmon resonance (LSPR) and can be used in applications such as surface-enhanced Raman scattering (SERS). Past research has focused on designing nanoparticles with complex structures to reveal their unique light-matter interactions.
Recently,Department of Chemistry, Sungkyunkwan UniversityPark Ho-seokProfessor, Department of Chemistry, Yonsei UniversityOh Man-hyunProfessor, Department of Chemistry, Sungkyunkwan UniversityKim Myung-wooProfessorTeamAn Au octahedral nanosponge was constructed for near-field focusing of three-dimensional plasmonic nanolenses. The study, titled "Au Octahedral Nanosponges: 3D Plasmonic Nanolenses for Nearfield Focusing", was published in the Journal of the American Chemical Society.
A multi-step method for the synthesis of Au OH NSS is shown in Figure 1. The synthesis consists of five chemical steps that can be performed on demand: (step 1) edge selective deposition of PT, (step 2) selective etching of internal AU, (step 3) concentric growth of AU, (step 4) eccentric growth of AG, and (step 5) electroexchange reactions. Inside the Au OH NSS there are sponge-like porous structures that help to enhance the scattering and absorption of incident light and transfer light energy to the nanospheres at the apex, enabling near-field focusing. The authors optimized the morphological dimensions of spheroids and porous structures by single-particle surface-enhanced Raman scattering (SERS) for the most efficient near-field focusing. In addition, the detection of SERS for weakly adsorbed molecules (2-chloroethylphenyl sulfide) and non-adsorbed species (methyl dimethyl methylphosphonate) was successfully achieved by using Au OH NSS and metal-organic frameworks as a mixed SERS substrate for gas adsorption interlayers.
Figure 1Schematic diagram of the synthesis process of AU octahedral nanosponge.
In conclusion, the authors report a highly sensitive and efficient SERS detection of gas-phase molecules using AU OH NSS, in which a high-density internal void (inside the sponge) and a spheroid tip strongly collect incident light for electromagnetic near-field focusing. Importantly, multiple scattering along the metallic ligaments in the inner region of the sponge strongly localizes the near field at the spherical tip, resulting in maximized enhancement. By optimizing the structure size of the AU OH NSS, a strong and clear 2-NTT SPSERS signal was obtainedSimilar solids such as Au Oh NPS and Au Oh NFS cannot display these signals without a porous structure. After assembly, the SERS substrate of Au OH NS shows a highly sensitive CEPS detection limit at 10 ppb. In addition, when Au OH NSS is combined with the MOF membrane as an intermediate gas adsorption layer, the gas phase detection ability of the non-metallic adsorbed molecule DMMP is enhanced.
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