Highly Aligned Plasmonic Gold Nanorods in a DNA Matrix

Abstract

Since the Lycurgus Cup was made in the 4th century, metal nanoparticles have attracted much interest due to the characteristics of the plasmonic and metamaterials that show beautiful colors. Despite these fascinating properties, the practical use is limited because it is difficult to control the orientation of the plasmonic nanoparticles. Here, highly aligned plasmonic gold nanorods are obtained using self-assembled DNA material. Simple mechanical shearing results in long-range DNA-gold nanorod arrays which show parallel, perpendicular, and zigzag configurations due to the competition between the shear force and DNA elasticity. The resulting surface plasmonic resonance properties of the aligned DNA-gold nanorods film show highly polarization-dependent behavior in a large area, which is critical for optical and photonic applications. This simple way to form anisotropic plasmonic films can be used for plasmonic nanoparticles in potential applications such as displays and sensors.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201703790.Recently, a few methods for controlling the GNRs based on the liquid crystal (LC) material used as a host medium were suggested to control the guest material-GNRs with external stimuli such as electric field, [21] magnetic field, [22] and mechanical force, [9] in which GNRs are spontaneously arranged with the LC director [9,21,[23][24][25] or trapped in the defect of LCs. [26] Among the various types of host LC materials, it is well known that lyotropic LC (LLC) is the most promising candidate for controlling GNRs because LLC itself is dispersed in the solvent, making it easy to homogeneously mix with GNR. Indeed, the phase transition occurs as a function of the solute concentration, here LLC material and GNR, meaning that various conformations of GNR can be achieved. LLC is found in condensed biomaterials such as DNA, [27,28] food dyes, [29] cellulose, [30,31] collagen, [32,33] and bacteriophage, [34,35] which are abundantly produced every year. Among these LLC materials, DNA extracted from plant or fish are easy to get and indeed very cheap compared with typical synthetic polymers and LC materials used in the practical applications. Particularly, DNA can be used as a building block to make small structures since DNA has the specific sequences that can be spontaneously assembled together to make the programmable structure such as origami. [36,37] Here, we fabricate well-oriented GNRs in DNA medium. Compared with other LLC, the orientation of DNA is easily controlled by applying simple mechanical shearing [38][39][40] (Table S1, Supporting Information). Thus, the DNA was selected as the medium to orient GNRs. The DNA material used in this study is salmon sperm DNA duplex (purchased from Sigma-Aldrich, St. Louis, MO, USA) with a Gaussian distribution in base pairs, for which the center point is ≈2000 base pairs and the corresponding length is ≈680 nm. [41] The DNA material in aqueous solution forms the LLC phase at t...

Microstructure arrays of DNA using topographic control

“…The extinction colours, blue and red of the DNA-GNR film were correlated with the longitudinal and transverse modes, resulting from the size of the GNR, which was 45 nm long and 15 nm in diameter (the inset in Fig. 5a) 22 . With varying angle, the extinction colours under a polarizer appeared bluish-grey (Fig.…”

“…When the concentration is further increased by evaporation of the solvent, such as water, a crystallised columnar phase (Cr) is formed, with little structural change 17 . Several methods have been proposed for preparing well-ordered and oriented DNA material in the LC phase, including simple drying 18,19 , mechanical shearing 20 or combing 21,22 , topographic confinement 23 and magnetic ordering 24 . However, these techniques only form relatively simple structures, such as unidirectional aligned DNA textures or irregular zigzag morphologies.…”

Generation of 2D DNA Microstructures via Topographic Control and Shearing

“…Deoxyribonucleic acid (DNA) is one of the candidates for building block to make chiral nano‐ and microstructures due to its regular structural features at the nanometer scale. [ 1,2 ] This unique structural property could make DNA material be used in templating applications to guide various kinds of nanomaterials as rationalized in alignment layer, [ 3–5 ] anisotropic matrix, [ 6,7 ] metallization, [ 8–10 ] and lithographic use. [ 11,12 ] The chemical functions of DNA also enable to realize electrooptic devices, [ 13–15 ] photonic, [ 16,17 ] and electronics.…”

“…The structure of DNA possesses regular topographic and chemical characteristics that are essential for the scaffold to guide a variety of nanomaterials, including anisotropic particles. [ 6,13 ] Based on this idea, a rod‐type thermotropic LC material, 4′‐ N ‐octyl‐4‐cyano‐biphenyl (8CB) is spin‐coated on the resultant DNA microstructure, and the thermal phase transition is directly observed . In the isotropic temperature (≈45 °C) of 8CB, the birefringence of only DNA chains is observed through the isotropic 8CB layer, which is the reason why the reddish domains are found ( Figure a).…”

“…Pulling speed of the substrate determines the molecular orientation in the thin film, and is about ≈1 cm s −1 in Figure 1c, which makes the DNA chains parallel to the pulling direction on the flat substrate. [ 6 ] The director of DNA chain, n DNA can be directly characterized by POM using the first‐order retardation or λ plate (λ = 530 nm) at 45° placed between a sample and a polarizer (Figure 1b,d,f). The slow axis of the λ‐plate is described with a pink arrow in the inset of Figure 1b.…”