DNA-Guided Close-Coupled Plasmonic "Polyatomic Molecules".

DNA-programmable assembly brings an utmost ideal way to realize designer plasmonic "molecules." However, due to richly existent structural variants, it is very hard to build strongly coupled multi-particle nanomolecules with a prescribed conformation. This work aims to address such a conformation-control dilemma, which has prohibited DNA-guided, strongly coupled plasmonic metamaterials from evolving into 3D "polyatomic" systems. A DNA tetrahedron is utilized to guide the assembly of coplanar (2D) triangular and nonplanar (3D) tetrahedral suprastructures of gold nanoparticles (AuNPs). Among various structural variants of these assemblies, the ones with D3h (trimer) and Td (tetramer) symmetries are particularly important, which are conformal in symmetry to the DNA framework. Our research further discloses that a water-miscible solvent of acetonitrile is good at driving strong coupling of DNA-bonded AuNP trimers and tetramers into close-packed plasmonic molecules, while maintaining their D3h and Td symmetries, respectively. The resulting strongly coupled AuNP clusters can be fixed in high-fidelity by Ag+ soldering. This success is attributed to the unique roles of acetonitrile in altering the interfacial/colloidal behaviors of AuNPs and DNA's mechanical properties, enabling cooperative/simultaneous close-packing of all AuNPs in an assembly. Our work opens up an avenue toward DNA-guided, close-coupled, higher-order plasmonic molecules for functional metamaterials.