Concave gold bipyramids bound with multiple high-index facets: improved Raman and catalytic activities.

Concave nanocrystals usually exhibit a large electromagnetic-field enhancement and superior catalytic performance due to their sharp corners, negative curvature and high-index facets. Conventional gold bipyramids (AuBPs) possess intriguing plasmonic properties which are attractive for various applications while the surface curvature of the reported bipyramids has not been fine-tuned to concave or convex structures to date. Additionally, the longitudinal surface plasmon resonance (LSPR) wavelengths of conventional AuBPs are mostly located in the range of 650-1350 nm and the sizes of these nanoparticles are usually not beyond 350 nm, which are not facilitated to some nano-focusing and nanophotonic applications. Herein, we reported a facile and robust approach for fabricating concave AuBPs (CAuBPs) with multiple high-index facets which are distinct from the conventional AuBPs and nanojavelin structures. The length of the as-prepared CAuBPs can even extend up to 800 nm. The CAuBP nanoparticles exhibit a strikingly pronounced broader plasmonic tuning range (even exceeding 1800 nm) and provide much higher electromagnetic-field enhancements in comparison to the conventional AuBPs, which broaden the promising applications of CAuBPs for many single-particle analyses. More importantly, the surface-enhanced Raman scattering (SERS) signals of CAuBPs on the single-particle or aqueous solution both displayed an enhanced intensity compared to conventional AuBPs. The CAuBP nanoparticles also exhibited improved catalytic activity due to the incredible abundance of uncoordinated atoms as active sites.