Gold Tetrahedral Nanoframes with Mono-Rim or Dual-Rim Morphologies for Enhanced Near-Field Focusing in SERS

This study presents a synthesis method for Au tetrahedral nanoframes (Td NFs) through a rationally designed multiple-step process, followed by an investigation of their distinctively ordered self-assembly for enhanced performance in surface-enhanced Raman spectroscopy (SERS). Two distinct Au Td NF building blocks are synthesized, exhibiting mono-rim or dual-rim morphologies. The mono-rim structure lacks intra-nanogaps, whereas the dual-rim configuration features well-defined intra-nanogaps. The non-centrosymmetric Td NFs self-assemble into a distinctive antiparallel arrangement that alternates between the tip-up and face-up orientations of the Au Td NFs. This configuration results in the formation of both triply tip-to-tip and face-to-face nanogaps. The unique zigzag pattern exhibited strong electromagnetic field enhancement and extensive spatial hot zones, significantly amplifying near-field focusing and, consequently, the SERS effect. The near-field enhancement of Au Td NF assemblies is confirmed through finite element method simulations and experimentally validated by comparing bulk SERS measurements with those of Au octahedron NF assemblies, which tend to adopt a parallel face-to-tip alignment during assembly. Owing to the complex arrangement of multiple intra-nanogaps between the internal rim-to-rim interfaces and the four exposed facets, dual-rim Td NFs exhibited single-particle SERS activity, a capability not observed in analogous Td NFs with single rims.