Three-Dimensional Au Octahedral Nanoheptamers: Single-Particle and Bulk Near-Field Focusing for Surface-Enhanced Raman Scattering

Abstract

Herein, we present a synthetic approach to fabricate Au nanoheptamers composed of six individual Au nanospheres interconnected through thin metal bridges arranged in an octahedral configuration. The resulting structures envelop central Au nanospheres, producing Au nanosphere heptamers with an open architectural arrangement. Importantly, the initial Pt coating of the Au nanospheres is a crucial step for protecting the inner Au nanospheres during multiple reactions. As-synthesized Au nanoheptamers exhibit multiple hot spots formed by nanogaps between nanospheres, resulting in strong electromagnetic near-fields. Additionally, we conducted surface-enhanced Raman-scattering-based detection of a chemical warfare agent simulant in the gas phase and achieved a limit of detection of 100 ppb, which is 3 orders lower than that achieved using Au nanospheres and Au nanohexamers. This pseudocore−shell nanostructure represents a significant advancement in the realm of complex nanoparticle synthesis, moving the field one step closer to sophisticated nanoparticle engineering.

Open Cross-gap Gold Nanocubes with Strong, Large-Area, Symmetric Electromagnetic Field Enhancement for On-Particle Molecular-Fingerprint Raman Bioassays

“…In addition, compared to a tetramer without the AuNC core, OXNCs generated a highly enhanced EM field at the near-infrared plasmon mode wavelength, indicating that the coupling between the AuNC core and budding NC structures plays a vital role in EM field enhancement (Figure S5). This result corresponds to the previous reports where the inner core Au nanosphere can induce high electric field enhancement compared to the structures without the inner core …”

“…Further, introduction of diverse Raman dyes to the EM field-enhanced open gap regions is readily possible, and the types of Raman dyes do not affect the shell and nanogap morphology with the open nanogap nanoparticles. Recently, multistep synthetic pathways to form various plasmonic nanostructures with nanogaps have been reported. ,− However, there are still challenges in synthesizing open nanogaps with a well-defined gap size and shape in a simple and facile manner. Further, generating these few nm gaps over a large surface area of nanoparticles in a reproducible manner for Raman-dye-free direct sensing of biomolecules with their molecular fingerprint peaks, particularly for quantitative SERS, is very difficult.…”

3D Connected Plasmonic Octamers for Boosting Single-Particle Surface-Enhanced Raman Scattering

“…Numerous studies have been dedicated to the preparation of such PINs. − For instance, Au nanoparticles functionalized with DNA, polymers, or small molecules have undergone regrowth of a gold shell to yield core–shell structures with narrow intragaps. − However, compared with simple core–shell configurations, the allure of three-dimensional (3D) complex PINs is heightened by the abundance of interior gaps and voids capable of fostering robust near-field focusing. Recent investigations by the Park group have introduced a multistep synthetic methodology for constructing octahedral nanohexamers, nanoheptamers, and nanosponges, thereby paving the way for the fabrication of 3D complex PINs through wet chemistry. − Nevertheless, the complexity of these 3D PINs makes it inherently challenging for them to adapt from one configuration to another. Therefore, achieving a simple, reliable, and reproducible synthesis process of 3D complex PINs with precise structural tunability continues to pose a substantial challenge.…”