Gap-Dependent Coupling of Ag-Au Nanoparticle Heterodimers Using DNA Origami-Based Self-Assembly

We fabricate heterocomponent dimers built from a single 40 nm gold and a single 40 nm silver nanoparticle separated by sub-5 nm gaps. Successful assembly mediated by a specialized DNA origami platform is verified by scanning electron microscopy and energy-dispersive X-ray characterization. Dark-field optical scattering on individual dimers is consistent with computational simulations. Direct plasmonic coupling between each nanoparticle is observed in both experiment and theory only for these small gap sizes, as it requires the silver dipolar mode energy to drop below the energy of the gold interband transitions. A new interparticle-spacing-dependent coupling model for heterodimers is thus required. Such Janus-like nanoparticle constructs available from DNA-mediated assembly provide an effective tool for controlling symmetry breaking in collective plasmon modes.