Tunable Optical Activity Of Plasmonic Gold Dimers Assembled By DNA Origami

Chiral nanocrystals and nanostructures have attracted considerable attention in recent decades. However, the synthesis of artificial chiral nanomaterials, in the aspect of the structural and handedness control, is still time-consuming and costly process. In comparison, self-assembly is considered as an efficient method to enable the fabrication of three-dimensional chiral superstructures with a variety of geometries, such as tetrahedral and helical configurations, which mimicked the natural chiral molecules.In chiral nanostructures, the precise control of geometrical parameters, such as the spatial orientation, position of the nanoelements and inter-components separations, is critical for tuning CD signals. Structural DNA nanotechnology has been demonstrated as a programmable methodology for bottom-up fabrication of complex nanostructures with well-defined shapes and well-controlled functionalities. In particular, DNA origami, which is featured with unprecedented flexibility and spatial addressability, makes a programmable breadboard for placement of a variety of nanoscale objects. In addition, DNA origami template has been used for site-selectively immobilized metal nanoparticles with nanometer precision. Notably, the assembly of noble metals nanoparticles, such as gold, can be directed by DNA origami template to achieve geometrical regulation of the nanoparticles construction, resulting in the controllable models of interparticle plasmon resonance and tunable field-enhancement effects.The asymmetric frame, integrating the dynamic Coulombic dipole-dipole and electromagnetic interactions, resulted in chiral response with controllable CD shape and intensity in the visible wavelength range, demonstrating the great potential of DNA origami in the construction of chiral artificial plasmonic nanostructures.In this paper, with DNA rectangular origami as the template we fabricated side-by-side AuNRs dimers and AuNS-AuNR asymmetric directed heterodimers nanoarchitectures. And the structural property and CD signals are studied. The main investigative contents and conclusions as following:1. We investigate the optical response of nanocomplexes of Au nanorod (AuNR)/Au nanosphere (AuNS) dimmers precisely assembled on DNA origami template.2. Plasmonic circular dichroism (CD) was found to be highly dependent on the orientation of the dimers relative to DNA axis and the inter-rod distances. The experimental results for the plasmonic CD of the dimers agreed well with theoretical calculations.3. With same inter-rod distances, two AuNRs/AuNSs assembled on the same side or different side of origami template showed distinct optical response. Dipole-dipole distances play a critical role in the induced plasmonic chirality.