Thermally Driven Plasmonic Coupling of DNA-Bonded Silver Nanodimers in Dispersion

DNA nanotechnology offers an unrivaled chance to construct plasmonic nanoassemblies with utmost precision. However, the relatively bulky DNA bonds that interconnect nanoparticle building units hinder an effective plasmon hybridization within the as-formed structures. In particular, there is a serious lack of a suitable method to achieve strong nearfield coupling of DNA-bonded silver nanoparticle (AgNP) assemblies in a commonly encountered aqueous chemical environment toward applications where plasmonically enhanced light-matter interactions play a critical role. Herein we present a simple, clean, and reagentless strategy to build strongly coupled homo- and hetero-dimeric plasmonic assemblies containing AgNPs under the guidance of DNA bonding. Such an emerging process utilizes heating-promoted oxidative co-stripping of Ag+/ligand complexes to partially disrupt the passivating layers on AgNPs, leading to reduced electrostatic and steric repulsions between DNA-linked AgNPs and thus enhanced colloidal coupling via van der Waals forces. This method is further adapted to make compositionally asymmetric heterodimeric assemblies comprising AgNPs and Au nanoparticles (AuNPs). The resulting structures featuring a sub-1.5 nm interparticle gap separation enable a highly efficient bonding dipole plasmon (BDP) hybridization to generate boosted light fields localized in the nanosized gaps. The thermally induced, strongly coupled AgNP dimers are stable in a low-salt aqueous solution during a long term storage, providing a novel class of DNA-programmable and plasmonically active materials. The less-damping plasmonic properties and the relatively higher chemical activities of AgNPs in comparison with AuNPs make the BDP-coupled AgNP dimers especially attractive for applications including surface-enhanced Raman scattering, plasmon-mediated photocatalysis, as well as chiral and nonlinear optics.