Construction of three-dimensional (3D) plasmonic architectures using structural DNA nanotechnology is an emerging multidisciplinary area of research. This technology excels in controlling spatial addressability at sub-10 nm resolution, which has thus far been beyond the reach of traditional top-down techniques. In this paper, we demonstrate the realization of 3D plasmonic chiral nanostructures through programmable transformation of gold nanoparticle (AuNP)-dressed DNA origami. AuNPs were assembled along two linear chains on a two-dimensional rectangular DNA origami sheet with well-controlled positions and particle spacing. By rational rolling of the 2D origami template, the AuNPs can be automatically arranged in a helical geometry, suggesting the possibility of achieving engineerable chiral nanomaterials in the visible range.

Molecular chemistry offers a unique toolkit to draw inspiration for the design of artificial metamolecules. For a long time, optical circular dichroism has been exclusively the terrain of natural chiral molecules, which exhibit optical activity mainly in the UV spectral range, thus greatly hindering their significance for a broad range of applications. Here we demonstrate that circular dichroism can be generated with artificial plasmonic chiral nanostructures composed of the minimum number of spherical gold nanoparticles required for three-dimensional (3D) chirality. We utilize a rigid addressable DNA origami template to precisely organize four nominally identical gold nanoparticles into a three-dimensional asymmetric tetramer. Because of the chiral structural symmetry and the strong plasmonic resonant coupling between the gold nanoparticles, the 3D plasmonic assemblies undergo different interactions with left and right circularly polarized light, leading to pronounced circular dichroism. Our experimental results agree well with theoretical predictions. The simplicity of our structure geometry and, most importantly, the concept of resorting on biology to produce artificial photonic functionalities open a new pathway to designing smart artificial plasmonic nanostructures for large-scale production of optically active metamaterials.

We show hierarchical assembly of plasmonic toroidal metamolecules that exhibit tailored optical activity in the visible spectral range. Each metamolecule consists of four identical origami-templated helical building blocks. Such toroidal metamolecules show a stronger chiroptical response than monomers and dimers of the helical building blocks. Enantiomers of the plasmonic structures yield opposite circular dichroism spectra. Experimental results agree well with the theoretical simulations. We also show that given the circular symmetry of the structures s distinct chiroptical response along their axial orientation can be uncovered via simple spin-coating of the metamolecules on substrates. Our work provides a new strategy to create plasmonic chiral platforms with sophisticated nanoscale architectures for potential applications such as chiral sensing using chemically based assembly systems.

3D plasmonic chiral colloids are synthesized through deterministically grouping of two gold nanorod AuNRs on DNA origami. These nanorod crosses exhibit strong circular dichroism (CD) at optical frequencies which can be engineered through position tuning of the rods on the origami. Our experimental results agree qualitatively well with theoretical predictions.The asset of DNA as nature's designer toolkit for structural technology has been explored for several decades. 1-5 The excellent control over topology and superior accuracy in templated synthesis bestow DNA the most successful molecule for programmable assembly of matter on the nanoscale. 6-10 The DNA origami technique, introduced by Rothemund, 11 relies on the nanoscale folding of a single-stranded viral DNA by numerous helper strands to create arbitrary 2D or 3D shapes. [11][12][13][14][15][16][17][18] Due to the fact that each individual helper strand can be modied and extended to produce a sequence-dependent surface tag, DNA origami can serve as a template to assemble functionalized nanoparticles. [19][20][21][22][23][24] Signicant progress in DNA origami technology has been concurrent with the prompt spanning of the scope of utility and diversity of possible conjugate materials. Among them, metal nanoparticles are one of the most exciting materials, whose versatile contributions in multiple disciplines have been indisputably witnessed. 25 A metal nanoparticle supports localized surface plasmons, which are associated with the collective oscillation of the conductive electrons in the nanoparticle. The localized nature of particle plasmons enables a vast range of useful applications, including surface-enhanced optical spectroscopies and subwavelength photonic devices, as well as medical diagnostics and therapeutics.Recently, considerable effort has been directed towards DNA origami templated assembly of gold nanoparticles into assortments of functional nanostructures. 26,27 Optical chirality in the visible spectral range is one of the most important pursuits in that it generally does not occur in natural chiral molecules. Recent seminal work was carried out by organizing gold spherical nanoparticles in a helical staircase on a DNA origami bundle. 28 However, due to the weak interaction between tiny gold nanoparticles, CD of these plasmonic helices was rather small. Alternatively, AuNRs have been considered owing to their excellent optical properties and stronger oscillator strength. For example, AuNRs were assembled on DNA origami to form chiral nanostructures. 29 However, the achieved CD response was still quite weak and the induced chiral effect due to the presence of DNA was not considered.Here we demonstrate 3D plasmonic chiral colloids assembled by DNA origami. Assemblies of crossed AuNRs templated by DNA origami are dispersed in a water-based solution. In each structure, two AuNRs are assembled on the opposite surfaces of a planar DNA origami sheet, forming a 90 twisting angle (see Fig. 1). Such crossed AuNRs constitute the simplest chiral object i...