High‐Yield Synthesis of Au@Ag Right Bipyramids and Self‐Assembly into Four‐Leaf‐Clover‐like Structures

Abstract Bimetallic core–shell nanostructures are of great interest because of their unique properties. Although bimetallic core–shell nanostructures with plenty of shapes are prepared, synthesis of core–shell nanostructures with asymmetric core and shells is still elusive. This work reports a facile seed‐mediated synthesis of Au@Ag right bipyramids with high yield (>95%) and broadly tunable edge length (from ≈130 to ≈230 nm) as well as tunable localized surface plasmon resonance properties. For the first time, a four‐leaf‐clover‐like tetramer of bipyramids is obtained through self‐assembly of the synthesized Au@Ag right bipyramids. The as‐assembled structure performs well in surface‐enhanced Raman spectroscopy with an analytical enhancement factor up to 1.4 × 107 because of the existence of both sharp tips and “hot‐spots.” The present work not only develops a new kind of nanomaterials, but also shows promising applications in optics and sensing.