Fivefold Symmetry‐Retained Formation of Pentagrammic Nanorattles Through Galvanic Replacement With Co‐Reduction

ABSTRACT

We report a fivefold symmetry–retained transformation of pentatwinned Au@Ag nanorods into non‐convex pentagrammic prism nanorattles through galvanic replacement coupled with ascorbic acid‐mediated co‐reduction. The coupled redox process enables facet‐selective growth while preserving the underlying pentatwinned symmetry, yielding hollow nanorattles composed of a solid Au core enclosed within a gold‐rich alloy shell featuring five ridged arms and concave pentagrammic caps. High‐resolution microscopy reveals anisotropic deposition localized between twin boundaries, while controlled kinetic modulation enables precise control over morphology evolution. The resulting nanostructure exhibits red‐shifted and broadened plasmonic modes and significantly enhanced SERS activity relative to rod‐shaped analogues. The retention of fivefold symmetry preserves the crystallographic equivalence of the pentagrammic architecture, contributing to a uniform plasmonic response and reproducible SERS performance. These findings establish a coupled galvanic replacement/co‐reduction strategy for engineering complex symmetry‐retained, concave plasmonic nanostructures with tailored optical properties.