3D plasmonic chiral colloids

Abstract

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...

Understanding complex chiral plasmonics

“…The CD spectra of the samples were measured by a Fourier-transform infrared spectrometer with attached polarizer and quarter-wave plate. This is different from the case of two interacting wires 27,[30][31][32] , in which the L-mode and T-mode are spectrally far separated. [17][18][19][20][21][22][23][24][25][26][27] In addition, we demonstrate that the observed optical phenomena can be analytically interpreted by an extended plasmonic Born-Kuhn model.…”

Chiral plasmonics

“…Shen and co-workers ( 62 ) also assembled chiral structures composed of two nanorods aligned tip to tip under a 90° angle (schematically illustrated in Fig. 4D).…”

Strong Chiroptical Activities in Gold Nanorod Dimers Assembled Using DNA Origami Templates

“…CD spectroscopy is widely used in the structural analysis of organic molecules and biomolecules, because the CD spectrum arises from the differential absorptions of left-and right-handed circularly polarized light for the molecular chiral center, In previous studies, DNA origami templates were widely considered as rigid, planar substrates for guiding the assembly of nanoparticles. 11,[16][17][18][19][20] In that case, the as-assembled AuNR dimer structures templated by the 2D DNA origami would not exhibit chiroptical activities according to our numerical simulations (discussed below). However, as observed in Figure 2b, the 'L' dimer assemblies obtained in our study exhibited significant CD signals.…”

“…[7][8][9] Furthermore, the handedness, wavelength and intensity of the plasmonic chirality can be rationally tuned by simply tailoring the geometry of the nanostructured components. [10][11][12][13] Recently, DNA origami has proved to be a versatile template for controlled assembly of noble metal nanoparticles, allowing the creation of well-defined plasmonic chiral nanostructures. For instances, tubular origami that displays helical arrangement of anchor sites enables organizing of threedimensional (3D) gold nanoparticle (AuNP) chiral plasmonic helices.…”