In a plasmonic molecule consisting of metal nanoparticles in close proximity, the surface plasmons of these nanoparticles can interact, mix, and hybridize in a fashion that is analogous to electronic wavefunctions in atomic and molecular orbitals. In particular, linear chains made of multiple nanospheres of different diameters were predicted to be substantially more effective in concentrating electric fields than dimer-based plasmonic structures. However, reproducibly aligning multiple nanospheres of disparate sizes into a linear chain remains beyond the capabilities of existing top-down and bottom-up approaches, making it difficult to study the plasmonic lensing effect as well as exploring the applications in sensing.<br/><br/>We herein report a new approach that uses a hollow DNA origami cage to exert sophisticated control over the 3D spatial arrangement of these particles. Instead of relying on 2D templates that interact with nanoparticles at one side, we used the cage to interact with multiple sides of the AuNPs and align the centers of the particles in a colinear configuration. Electron microscopy showed that our 3D hollow origami cage limits the bending angle to an average of only 10 degrees. UV-Vis measurements showed a longitudinal mode that is indicative of strong plasmonic coupling between these particles. SERS spectra showed signal enhancement consistent with FDTD simulations. Our new approach could pave the way for the synthesis of more complex hetero-multimeric plasmonic molecules for SERS sensing, wave guiding and experimental evaluations of plasmonic theories.

Self-assembly of linear trimeric plasmonic molecules using a 3D DNA origami template

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