Tetrahedron-Embedded Porous Cubic Nanoframes for Concurrent Engineering of Hotspot Intensity and Density.

Plasmonic nanostructures enable surface-enhanced Raman scattering (SERS) through nanoscale hotspots, where electromagnetic fields are strongly confined. Both hotspot intensity and density are critical for enhancing SERS, yet their individual contributions to SERS performance have not been directly compared within a structurally consistent system. Herein, we present four plasmonic nanostructures comprising a cubic nanoframe (CNF) with an identical outer geometry but a distinct internal architecture: hollow, tetrahedron-embedded, porous, or tetrahedron-embedded/porous to control hotspot intensity and density. Through single-particle and ensemble SERS measurements, we demonstrate that the tetrahedral solid core governs hotspot intensity while the porous domain controls hotspot density. Furthermore, hotspot intensity predominates SERS signal intensity at high analyte (2-naphthalenethiol) concentrations (10-4 to 10-8 M), whereas hotspot density becomes the critical determinant at low analyte concentrations (under 10-8 M). By preserving both characteristics, the tetrahedron-embedded porous CNF enabled superior peak resolution at high concentrations and reliable detection down to 10-15 M. This work demonstrates a reliable structure-property framework for the rational design of plasmonic-sensing platforms with simultaneously optimized signal intensity and detection sensitivity.