Ensemble hot-spots in 3D supercrystals of plasmonic octahedral nanoparticles in tip-to-tip configured superlattices.

Nanoparticle assembly offers promising strategy for harnessing the physicochemical interparticle interactions. Despite its potential for boosting light-matter interaction, achieving nanoparticle assembly with tip-to-tip manner remains a significant challenge. Here we show a synthetic procedure for organizing gold octahedral nanoparticles into a distinct three-dimensional upright superstructure, where the pointed tips are oriented toward neighboring nanoparticles to promote enhanced near-field focusing at these apexes. This arrangement, referred to as the "coupling of the lightning rod effect", facilitates production in the form of "superpowder", which exhibits an extensive assembly order like a powder. Deviating from natural packing principles, this tip-to-tip alignment-the upright octahedral superlattice-optimizes near-field focusing on its vertices while maintaining consistently high porosity, allowing for deep penetration of adsorbates. This configuration is advantageous for enabling surface-enhanced Raman scattering of gaseous molecules with reduced background fluorescence signals, particularly under high-intensity laser excitation, a challenging feat with conventional surface-enhanced Raman scattering techniques.