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

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-cloverlike 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. [ABSTRACT FROM AUTHOR]