DNA has become one of the most extensively used molecular building blocks for engineering self-assembling materials. DNA origami is a technique that uses hundreds of short DNA oligonucleotides, called staple strands, to fold a long single-stranded DNA, which is called a scaffold strand, into various designer nanoscale architectures. DNA origami has dramatically improved the complexity and scalability of DNA nanostructures. Due to its high degree of customization and spatial addressability, DNA origami provides a versatile platform with which to engineer nanoscale structures and devices that can sense, compute, and actuate. These capabilities open up opportunities for a broad range of applications in chemistry, biology, physics, material science, and computer science that have often required programmed spatial control of molecules and atoms in three-dimensional (3D) space. This review provides a comprehensive survey of recent developments in DNA origami structure, design, assembly, and directed self-assemb...

DNA Origami: Scaffolds for Creating Higher Order Structures

Over the past three decades DNA has emerged as an exceptional molecular building block for nanoconstruction due to its predictable conformation and programmable intra- and intermolecular Watson–Crick base-pairing interactions. A variety of convenient design rules and reliable assembly methods have been developed to engineer DNA nanostructures of increasing complexity. The ability to create designer DNA architectures with accurate spatial control has allowed researchers to explore novel applications in many directions, such as directed material assembly, structural biology, biocatalysis, DNA computing, nanorobotics, disease diagnosis, and drug delivery. This Perspective discusses the state of the art in the field of structural DNA nanotechnology and presents some of the challenges and opportunities that exist in DNA-based molecular design and programming.

Structural DNA Nanotechnology: State of the Art and Future Perspective

Plasmonic sensors are extremely promising candidates for label-free single-molecule analysis but require exquisite control over the physical arrangement of metallic nanostructures. Here we employ self-assembly based on the DNA origami technique for accurate positioning of individual gold nanoparticles. Our innovative design leads to strong plasmonic coupling between two 40 nm gold nanoparticles reproducibly held with gaps of 3.3±1 nm. This is confirmed through far field scattering measurements on individual dimers which reveal a significant red shift in the plasmonic resonance peaks, consistent with the high dielectric environment due to the surrounding DNA. We use surface-enhanced Raman scattering (SERS) to demonstrate local field enhancements of several orders of magnitude through detection of a small number of dye molecules as well as short single-stranded DNA oligonucleotides. This demonstrates that DNA origami is a powerful tool for the high-yield creation of SERS-active nanoparticle assemblies with reliable sub-5 nm gap sizes. DNA origami is a versatile fabrication approach for building tailored nanostructures. Thacker et al.apply it to the assembly of gold nanoparticle dimers with sub-5 nm gaps and show how the resulting plasmonic resonances can be exploited for surface-enhanced Raman scattering.

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DNA origami based assembly of gold nanoparticle dimers for surface-enhanced Raman scattering

Based on electronic structure and atomic size considerations, nitrogen has been regarded as the most suitable impurity for p-type doping in ZnO. However, numerous experimental efforts by many different groups have not resulted in stable and reproducible p-type material, casting doubt on the efficacy of nitrogen as a shallow acceptor. Based on advanced first-principles calculations we find that nitrogen is actually a deep acceptor, with an exceedingly high ionization energy of 1.3 eV, and hence cannot lead to hole conductivity in ZnO. In light of this result, we reexamine prior experiments on nitrogen doping of ZnO.

http://absimage.aps.org/image/MAR10/MWS_MAR10-2009-001476.pdf

Why nitrogen cannot lead to p-type conductivity in ZnO

Circular dichroism spectra of naturally occurring molecules and also of synthetic chiral arrangements of plasmonic particles often exhibit characteristic bisignate shapes. Such spectra consist of peaks next to dips (or vice versa) and result from the superposition of signals originating from many individual chiral objects oriented randomly in solution. Here we show that by first aligning and then toggling the orientation of DNA-origami-scaffolded nanoparticle helices attached to a substrate, we are able to reversibly switch the optical response between two distinct circular dichroism spectra corresponding to either perpendicular or parallel helix orientation with respect to the light beam. The observed directional circular dichroism of our switchable plasmonic material is in good agreement with predictions based on dipole approximation theory. Such dynamic metamaterials introduce functionality into soft matter-based optical devices and may enable novel data storage schemes or signal modulators.

/pdf/chiral-plasmonic-dna-nanostructures-with-switchable-circular-3la9j5karj.pdf

Chiral plasmonic DNA nanostructures with switchable circular dichroism

DNA origami templated self-assembly has shown its potential in creating rationally designed nanophotonic devices in a parallel and repeatable manner. In this investigation, we employ a multiscaffold DNA origami approach to fabricate linear waveguides of 10 nm diameter gold nanoparticles. This approach provides independent control over nanoparticle separation and spatial arrangement. The waveguides were characterized using atomic force microscopy and far-field polarization spectroscopy. This work provides a path toward large-scale plasmonic circuitry.

/pdf/multiscaffold-dna-origami-nanoparticle-waveguides-6m5a1knzb4.pdf

Multiscaffold DNA Origami Nanoparticle Waveguides

High precision, high yield, and high density self-assembly of nanoparticles into arrays is essential for nanophotonics. Spatial deviations as small as a few nanometers can alter the properties of near-field coupled optical nanostructures. Several studies have reported assemblies of few nanoparticle structures with controlled spacing using DNA nanostructures with variable yield. Here, we report multi-tether design strategies and attachment yields for homo- and hetero-nanoparticle arrays templated by DNA origami nanotubes. Nanoparticle attachment yield via DNA hybridization is comparable with streptavidin-biotin binding. Independent of the number of binding sites, >97% site-occupation was achieved with four tethers and 99.2% site-occupation is theoretically possible with five tethers. The interparticle distance was within 2 nm of all design specifications and the nanoparticle spatial deviations decreased with interparticle spacing. Modified geometric, binomial, and trinomial distributions indicate that site-bridging, steric hindrance, and electrostatic repulsion were not dominant barriers to self-assembly and both tethers and binding sites were statistically independent at high particle densities.

/pdf/high-precision-and-high-yield-fabrication-of-dense-286ro9gyq4.pdf

High precision and high yield fabrication of dense nanoparticle arrays onto DNA origami at statistically independent binding sites

Synthesis and characterization of [Zn(acetate)2(amine)x] compounds (x=1 or 2) and their use as precursors to ZnO

We present experimental evidence that trapping mechanisms contributing to the negative bias temperature instability (NBTI) of high-k dielectric p-channel metal oxide semiconductor (pMOS) transistors are thermally activated. Device behavior during stress and recovery from 300 K down to 6 K indicate the dominance of the hole trapping mechanism commonly attributed to NBTI is reduced as temperature decreases. Further, trends in the temperature dependence of drain current shifts suggest more than one mechanism is responsible for NBTI. Specifically, below 240 K, current degradation immediately following stress is no longer observed. In fact, the opposite effect occurs, which is suggestive of electron trapping as the dominant mechanism at such temperatures.

/pdf/cryogenic-to-room-temperature-effects-of-nbti-in-high-k-pmos-2bs3yn398q.pdf

Blake Rapp

Papers

Multiscaffold DNA Origami Nanoparticle Waveguides

High precision and high yield fabrication of dense nanoparticle arrays onto DNA origami at statistically independent binding sites

Synthesis and characterization of [Zn(acetate)2(amine)x] compounds (x=1 or 2) and their use as precursors to ZnO

Cryogenic to room temperature effects of NBTI in high-k PMOS devices