Four-Point Probe Electrical Measurements on Templated Gold Nanowires Formed on Single DNA Origami Tiles

DNA-Templated Nanofabrication of CdS-Au Nanoscale Schottky Contacts and Electrical Characterization

DNA-templated nanofabrication presents an innovative approach to creating self-assembled nanoscale metal-semiconductor-based Schottky contacts, which can advance nanoelectronics. Herein, we report the successful fabrication of metal-semiconductor Schottky contacts using a DNA origami scaffold. The scaffold, consisting of DNA strands organized into a specific linear architecture, facilitates the competitive arrangement of Au and CdS nanorods, forming heterojunctions, and addresses previous limitations in low electrical conductance making DNA-templated electronics with semiconductor nanomaterials. Electroless gold plating extends the Au nanorods and makes the necessary electrical contacts. Tungsten electrical connection lines are further created by electron beam-induced deposition. Electrical characterization reveals nonlinear Schottky barrier behavior, with electrical conductance ranging from 0.5 × 10-4 to 1.7 × 10-4 S. The conductance of these DNA-templated junctions is several million times higher than with our prior Schottky contacts. Our research establishes an innovative self-assembly approach with applicable metal and semiconductor materials for making highly conductive nanoscale Schottky contacts, paving the way for the future development of DNA-based nanoscale electronics.

Metallic Nanowires Self-Assembled in Quasi-Circular Nanomolds Templated by DNA Origami

The self-assembly of conducting nanostructures is currently being investigated intensively in order to evaluate the feasibility of creating novel nanoelectronic devices and circuits using such pathways. In particular, methods based on so-called DNA Origami nanostructures have shown great potential in the formation of metallic nanowires. The main challenge of this method is the reproducible generation of very well-connected metallic nanostructures, which may be used as interconnects in future devices. Here, we use a novel design of nanowires with a quasi-circular cross-section as opposed to rectangular or uncontrolled cross-sections in earlier studies. We find indications that the reliability of the fabrication scheme is enhanced and the overall resistance of the wires is comparable to metallic nanostructures generated by electrochemistry or top-down methods. In addition, we observe that some of the nanowires are annealed when passing a current through them, which leads to a clear enhancement for the conductance. We envision that these nanowires provide further steps towards the successful generation of nanoelectronics using self-assembly.

Towards atom manufacturing with framework nucleic acids

Atom manufacturing has become a blooming frontier direction in the field of material and chemical science in recent years, focusing on the fabrication of functional materials and devices with individual atoms or with atomic precision. Framework nucleic acids (FNAs) refer to nanoscale nucleic acid framework structures with novel properties distinct from those of conventional nucleic acids. Due to their ability to be precisely positioned and assembled at the nanometer or even atomic scale, FNAs are ideal materials for atom manufacturing. They hold great promise for the bottom-up construction of electronic devices by precisely arranging and integrating building blocks with atomic or near-atomic precision. In this review, we summarize the progress of atom manufacturing based on FNAs. We begin by introducing the atomic-precision construction of FNAs and the intrinsic electrical properties of DNA molecules. Then, we describe various approaches for the fabrication of FNAs templated materials and devices, which are classified as conducting, insulating, or semiconducting based on their electrical properties. We highlight the role of FNAs in the fabrication of functional electronic devices with atomic precision, as well as the challenges and opportunities for atom manufacturing with FNAs.

Block copolymer self-assembly to pattern gold nanodots for site-specific placement of DNA origami and attachment of nanomaterials

Directed placement of DNA origami could play a key role in future integrated nanoelectronic devices. Here we demonstrated the site-selective attachment of DNA origami on gold dots formed using a pattern transfer method through block copolymer self-assembly. First, a random copolymer brush layer is grafted on the Si surface and then poly (styrene-b-methylmethacrylate) block copolymer is spin-coated to give a hexagonal nanoarray after annealing. UV irradiation followed by acetic acid etching is used to remove the PMMA, creating cylindrical holes and then oxygen plasma etching removes the random copolymer layer inside those holes. Next, metal evaporation, followed by lift-off creates a gold dot array. We evaluated different ligand functionalization of Au dots, as well as DNA hybridization to attach DNA origami to the nanodots. DNA-coated Au nanorods are assembled on the DNA origami as a step towards creating nanowires and to facilitate electron microscopy characterization of the attachment of DNA origami on these Au nanodots. The DNA hybridization approach showed better DNA attachment to Au nanodots than localization by electrostatic interaction. This work contributes to the understanding of DNA-templated assembly, nanomaterials, and block copolymer nanolithography. Furthermore, the work shows potential for creating DNA-templated nanodevices and their placement in ordered arrays in future nanoelectronics.

Biomolecule-Based Optical Metamaterials: Design and Applications

Metamaterials are broadly defined as artificial, electromagnetically homogeneous structures that exhibit unusual physical properties that are not present in nature. They possess extraordinary capabilities to bend electromagnetic waves. Their size, shape and composition can be engineered to modify their characteristics, such as iridescence, color shift, absorbance at different wavelengths, etc., and harness them as biosensors. Metamaterial construction from biological sources such as carbohydrates, proteins and nucleic acids represents a low-cost alternative, rendering high quantities and yields. In addition, the malleability of these biomaterials makes it possible to fabricate an endless number of structured materials such as composited nanoparticles, biofilms, nanofibers, quantum dots, and many others, with very specific, invaluable and tremendously useful optical characteristics. The intrinsic characteristics observed in biomaterials make them suitable for biomedical applications. This review addresses the optical characteristics of metamaterials obtained from the major macromolecules found in nature: carbohydrates, proteins and DNA, highlighting their biosensor field use, and pointing out their physical properties and production paths.

Fabrication of High Aspect Ratio Gold Nanowires within the Microtubule Lumen

Gold nanowires have great potential use as interconnects in electronic, photonic, and optoelectronic devices. To date, there are various fabrication strategies for gold nanowires, each one associated with particular drawbacks as they utilize high temperatures, toxic chemicals, or expensive compounds to produce nanowires of suboptimal quality. Inspired by nanowire fabrication strategies that used higher-order biopolymer structures as molds for electroless deposition of gold, we here report a strategy for the growth of gold nanowires from seed nanoparticles within the lumen of microtubules. Luminal targeting of seed particles occurs through covalently linked Fab fragments of an antibody recognizing the acetylated lysine 40 on the luminal side of α-tubulin. Gold nanowires grown by electroless deposition within the microtubule lumen exhibit a homogeneous morphology and high aspect ratios with a mean diameter of 20 nm. Our approach is fast, simple, and inexpensive and does not require toxic chemicals or other harsh conditions.

Engineering Inorganic Materials with DNA Nanostructures

Nucleic acid nanotechnology lays a foundation for the user-friendly design and synthesis of DNA frameworks of any desirable shape with extreme accuracy and addressability. Undoubtedly, such features make these structures ideal modules for positioning and organizing molecules and molecular components into complex assemblies. One of the emerging concepts in the field is to create inorganic and hybrid materials through programmable DNA templates. Here, we discuss the challenges and perspectives of such DNA nanostructure-driven materials science engineering and provide insights into the subject by introducing various DNA-based fabrication techniques including metallization, mineralization, lithography, casting, and hierarchical self-assembly of metal nanoparticles.

Gold Nanorods: The Most Versatile Plasmonic Nanoparticles

Gold nanorods (NRs), pseudo-one-dimensional rod-shaped nanoparticles (NPs), have become one of the burgeoning materials in the recent years due to their anisotropic shape and adjustable plasmonic properties. With the continuous improvement in synthetic methods, a variety of materials have been attached around Au NRs to achieve unexpected or improved plasmonic properties and explore state-of-the-art technologies. In this review, we comprehensively summarize the latest progress on Au NRs, the most versatile anisotropic plasmonic NPs. We present a representative overview of the advances in the synthetic strategies and outline an extensive catalogue of Au-NR-based heterostructures with tailored architectures and special functionalities. The bottom-up assembly of Au NRs into preprogrammed metastructures is then discussed, as well as the design principles. We also provide a systematic elucidation of the different plasmonic properties associated with the Au-NR-based structures, followed by a discussion of the promising applications of Au NRs in various fields. We finally discuss the future research directions and challenges of Au NRs.

Probing the Conformational States of a pH-Sensitive DNA Origami Zipper via Label-Free Electrochemical Methods

DNA origami structures represent an exciting class of materials for use in a wide range of biotechnological applications. This study reports the design, production, and characterization of a DNA origami "zipper" structure, which contains nine pH-responsive DNA locks. Each lock consists of two parts that are attached to the zipper's opposite arms: a DNA hairpin and a single-stranded DNA that are able to form a DNA triplex through Hoogsteen base pairing. The sequences of the locks were selected in a way that the zipper adopted a closed configuration at pH 6.5 and an open state at pH 8.0 (transition pK_a 7.6). By adding thiol groups, it was possible to immobilize the zipper structure onto gold surfaces. The immobilization process was characterized electrochemically to confirm successful adsorption of the zipper. The open and closed states were then probed using differential pulse voltammetry and electrochemical impedance spectroscopy with solution-based redox agents. It was found that after immobilization, the open or closed state of the zipper in different pH regimes could be determined by electrochemical interrogation. These findings pave the way for development of DNA origami-based pH monitoring and other pH-responsive sensing and release strategies for zipper-functionalized gold surfaces.

Bottom-Up Fabrication of DNA-Templated Electronic Nanomaterials and Their Characterization

Bottom-up fabrication using DNA is a promising approach for the creation of nanoarchitectures. Accordingly, nanomaterials with specific electronic, photonic, or other functions are precisely and programmably positioned on DNA nanostructures from a disordered collection of smaller parts. These self-assembled structures offer significant potential in many domains such as sensing, drug delivery, and electronic device manufacturing. This review describes recent progress in organizing nanoscale morphologies of metals, semiconductors, and carbon nanotubes using DNA templates. We describe common substrates, DNA templates, seeding, plating, nanomaterial placement, and methods for structural and electrical characterization. Finally, our outlook for DNA-enabled bottom-up nanofabrication of materials is presented.

Scaling Up DNA Origami Lattice Assembly

The surface-assisted hierarchical assembly of DNA origami nanostructures is a promising route to fabricate regular nanoscale lattices. In this work, the scalability of this approach is explored and the formation of a homogeneous polycrystalline DNA origami lattice at the mica-electrolyte interface over a total surface area of 18.75 cm2 is demonstrated. The topological analysis of more than 50 individual AFM images recorded at random locations over the sample surface showed only minuscule and random variations in the quality and order of the assembled lattice. The analysis of more than 450 fluorescence microscopy images of a quantum dot-decorated DNA origami lattice further revealed a very homogeneous surface coverage over cm2 areas with only minor boundary effects at the substrate edges. At total DNA costs of € 0.12 per cm2 , this large-scale nanopatterning technique holds great promise for the fabrication of functional surfaces.

Fabrication and temperature-dependent electrical characterization of a C-shape nanowire patterned by a DNA origami

We introduce a method based on directed molecular self-assembly to manufacture and electrically characterise C-shape gold nanowires which clearly deviate from typical linear shape due to the design of the template guiding the assembly. To this end, gold nanoparticles are arranged in the desired shape on a DNA-origami template and enhanced to form a continuous wire through electroless deposition. C-shape nanowires with a size below 150nm on a \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\hbox {SiO}_2}/\hbox {Si}$$\end{document}SiO2/Si substrate are contacted with gold electrodes by means of electron beam lithography. Charge transport measurements of the nanowires show hopping, thermionic and tunneling transports at different temperatures in the 4.2K to 293K range. The different transport mechanisms indicate that the C-shape nanowires consist of metallic segments which are weakly coupled along the wires.

Gold Nanowires from Nanorods

Gold nanowires (AuNWs) possess strong potential application in micro- and nanoelectronics as well as in plasmonic waveguides because of their low electrical resistance. However, the synthesis of pure solvent-dispersible AuNWs with full control over their length still remains a challenge. All the previously reported methods produce AuNWs with other impurities such as smaller nanorods, platelets, and spherical particles and are limited to a certain length (typically below 10 μm). This article describes a one-step synthesis of extremely long AuNWs (up to 25 μm) with great control over their dimensions by using pentahedrally twinned gold nanorods (AuNRs) as seed particles. To induce the AuNW growth, the reduction of Au(I) to Au(0) was carried out on the surface of AuNRs at a very low pH by introducing HCl into the growth solution. The slow conversion of Au(I) to Au(0) due to the increase in reduction potential at lower pH promoted the preferential deposition of metallic gold on the more reactive tips of AuNRs compared to their sides, resulting in the formation of AuNWs. In analogy to the "living" polymerization reaction, the length of the AuNWs was proportional to the amount of Au(I) added to the growth solution; thus, the desired length of AuNWs was achieved by controlling the supply of Au(I) ions in the reaction mixture. The AuNWs longer than 6 μm were found to be responsive to microwave radiation. When an aqueous solution of AuNWs was exposed to microwaves, the formation of sharp kinks was observed in several locations of AuNWs without their disintegration into smaller pieces.

Seeding, Plating and Electrical Characterization of Gold Nanowires Formed on Self-Assembled DNA Nanotubes

Self-assembly nanofabrication is increasingly appealing in complex nanostructures, as it requires fewer materials and has potential to reduce feature sizes. The use of DNA to control nanoscale and microscale features is promising but not fully developed. In this work, we study self-assembled DNA nanotubes to fabricate gold nanowires for use as interconnects in future nanoelectronic devices. We evaluate two approaches for seeding, gold and palladium, both using gold electroless plating to connect the seeds. These gold nanowires are characterized electrically utilizing electron beam induced deposition of tungsten and four-point probe techniques. Measured resistivity values for 15 successfully studied wires are between 9.3 × 10-6 and 1.2 × 10-3 Ωm. Our work yields new insights into reproducible formation and characterization of metal nanowires on DNA nanotubes, making them promising templates for future nanowires in complex electronic circuitry.

Intervening Bismuth Tungstate with DNA Chain Assemblies: A Perception toward Feedstock Conversion via Photoelectrocatalytic Water Splitting

An advanced approach with DNA-mediated bismuth tungstate (Bi₂WO₆) one-dimensional (1-D) nanochain assemblies for hydrogen production with 5-fold enhanced photoelectrochemical (PEC) water splitting reaction is presented. The creation of new surface states upon DNA modification mediates the electron transfer in a facile manner for a better PEC process. The UV-Vis-DRS analysis results a red shift in the optical absorption phenomenon with the interference of DNA modification on Bi₂WO₆, and, thus, the band gap was tuned from 3.05 eV to 2.71 eV. The applied bias photon-to-current efficiency (ABPE) was calculated and shows a maximum for the Bi₂WO₆@DNA-2 (25.22 × 10^-4%), compared to pristine Bi₂WO₆ (7.76 × 10^-4%). Furthermore, the idea of practical utility of produced hydrogen from PEC is established for the first time with photocatalytic feedstock conversion to platform chemicals using cinnamaldehyde, 2-hydroxy-1-phenylethanone, and 2-(3-methoxyphenoxy)-1-phenylethanone in large scale by hydrogenation and/or hydrogenolysis reactions under eco-friendly green conditions with external hydrogen pressure in an aqueous mixture. Also, the recyclability experiment delivered good yields, which further confirm the robustness of the developed catalyst.

Covalent Hyperbranched Polymer Self-Assemblies of Three-Way Junction DNA for Single-Molecule Devices

A hyperbranched polymer (HBP) made of three-way junction (TWJ) DNAs is reported. Three types of 26-mer DNAs with 5'-ends modified with psoralen (PSN) were synthesized. All had self-complementary sequences starting from the 5'-end to the sixth base (AAGCTT), allowing intermolecular hybridization. The base sequences of the remaining 20-mer sites were designed so that upon hybridization, three strands had a TWJ structure with a mass of 25,000 that could be further grown by forming HBPs. PSN photochemically reacts to form interstrand cross-links that increase the polymer stability. Aggregates [(380 ± 44) nm and (65 ± 6) nm] detected with dynamic light scattering for TWJ-DNA solutions were also imaged by electron microscopy and atomic force microscopy, providing evidence of hyperbranched polymerization. The TWJ unit also polymerized on solid substrates such as Au and glass and formed self-assembled monolayers (SAMs). The HBP SAMs were integrated into commercial Pt-interdigitated electrode arrays. The DNA devices had current-voltage curves typical of metal-insulator-metal Schottky diodes; the effective barrier heights and the ideality factors were 0.52 ± 0.002 eV and 21 ± 3.2, respectively. The series resistances were (26 ± 3.3) × 10⁶ Ω, which may provide insights into DNA electron transport. The DNA HBP enables stable electrical connections with probe electrodes and will be an important single-molecule platform.

An electrochemical biosensor exploiting binding-induced changes in electron transfer of electrode-attached DNA origami to detect hundred nanometer-scale targets

The specific detection in clinical samples of analytes with dimensions in the tens to hundreds of nanometers, such as viruses and large proteins, would improve disease diagnosis. Detection of these "mesoscale" analytes (as opposed to their nanoscale components), however, is challenging as it requires the simultaneous binding of multiple recognition sites often spaced over tens of nanometers. In response, we have adapted DNA origami, with its unparalleled customizability to precisely display multiple target-binding sites over the relevant length scale, to an electrochemical biosensor platform. Our proof-of-concept employs triangular origami covalently attached to a gold electrode and functionalized with redox reporters. Electrochemical interrogation of this platform successfully monitors mesoscale, target-binding-induced changes in electron transfer in a manner consistent with coarse-grained molecular dynamics simulations. Our approach enables the specific detection of analytes displaying recognition sites that are separated by ∼40 nm, a spacing significantly greater than that achieved in similar sensor architectures employing either antibodies or aptamers.

Impact of Polymer-Constrained Annealing on the Properties of DNA Origami-Templated Gold Nanowires

DNA origami-templated fabrication enables bottom-up fabrication of nanoscale structures from a variety of functional materials, including metal nanowires. We studied the impact of low-temperature annealing on the morphology and conductance of DNA-templated nanowires. Nanowires were formed by selective seeding of gold nanorods on DNA origami and gold electroless plating of the seeded structures. At low annealing temperatures (160 °C for seeded-only and 180 °C for plated), the wires broke up and separated into multiple, isolated islands. Through the use of polymer-constrained annealing, the island formation in plated wires was suppressed up to annealing temperatures of 210 °C. Four-point electrical measurements showed that the wires remained conductive after a polymer-constrained annealing at 200 °C.

Enhancing the stability of DNA origami nanostructures: staple strand redesign versus enzymatic ligation

DNA origami structures have developed into versatile tools in molecular sciences and nanotechnology. Currently, however, many potential applications are hindered by their poor stability, especially under denaturing conditions. Here we present and evaluate two simple approaches to enhance DNA origami stability. In the first approach, we elevated the melting temperature of nine critical staple strands by merging the oligonucleotides with adjacent sequences. In the second approach, we increased the global stability by enzymatically ligating all accessible staple strand ends directly. By monitoring the gradual urea-induced denaturation of a prototype triangular DNA origami modified by these approaches using atomic force microscopy, we show that rational redesign of a few, critical staple strands leads to a considerable increase in overall stability at high denaturant concentration and elevated temperatures. In addition, enzymatic ligation yields DNA nanostructures with superior stability at up to 37 °C and in the presence of 6 M urea without impairing their shape. This bio-orthogonal approach is readily adaptable to other DNA origami structures without the need for synthetic nucleotide modifications when structural integrity under harsh conditions is required.

Effect of Staple Age on DNA Origami Nanostructure Assembly and Stability

DNA origami nanostructures are widely employed in various areas of fundamental and applied research. Due to the tremendous success of the DNA origami technique in the academic field, considerable efforts currently aim at the translation of this technology from a laboratory setting to real-world applications, such as nanoelectronics, drug delivery, and biosensing. While many of these real-world applications rely on an intact DNA origami shape, they often also subject the DNA origami nanostructures to rather harsh and potentially damaging environmental and processing conditions. Furthermore, in the context of DNA origami mass production, the long-term storage of DNA origami nanostructures or their pre-assembled components also becomes an issue of high relevance, especially regarding the possible negative effects on DNA origami structural integrity. Thus, we investigated the effect of staple age on the self-assembly and stability of DNA origami nanostructures using atomic force microscopy. Different harsh processing conditions were simulated by applying different sample preparation protocols. Our results show that staple solutions may be stored at -20 °C for several years without impeding DNA origami self-assembly. Depending on DNA origami shape and superstructure, however, staple age may have negative effects on DNA origami stability under harsh treatment conditions. Mass spectrometry analysis of the aged staple mixtures revealed no signs of staple fragmentation. We, therefore, attribute the increased DNA origami sensitivity toward environmental conditions to an accumulation of damaged nucleobases, which undergo weaker base-pairing interactions and thus lead to reduced duplex stability.

Create Nanoscale Patterns with DNA Origami

Structural deoxyribonucleic acid (DNA) nanotechnology offers a robust platform for diverse nanoscale shapes that can be used in various applications. Among a wide variety of DNA assembly strategies, DNA origami is the most robust one in constructing custom nanoshapes and exquisite patterns. In this account, the static structural and functional patterns assembled on DNA origami are reviewed, as well as the reconfigurable assembled architectures regulated through dynamic DNA nanotechnology. The fast progress of dynamic DNA origami nanotechnology facilitates the construction of reconfigurable patterns, which can further be used in many applications such as optical/plasmonic sensors, nanophotonic devices, and nanorobotics for numerous different tasks.

Review of the Electrical Characterization of Metallic Nanowires on DNA Templates

The use of self-assembly techniques may open new possibilities in scaling down electronic circuits to their ultimate limits. Deoxyribonucleic acid (DNA) nanotechnology has already demonstrated that it can provide valuable tools for the creation of nanostructures of arbitrary shape, therefore presenting an ideal platform for the development of nanoelectronic circuits. So far, however, the electronic properties of DNA nanostructures are mostly insulating, thus limiting the use of the nanostructures in electronic circuits. Therefore, methods have been investigated that use the DNA nanostructures as templates for the deposition of electrically conducting materials along the DNA strands. The most simple such structure is given by metallic nanowires formed by deposition of metals along the DNA nanostructures. Here, we review the fabrication and the characterization of the electronic properties of nanowires, which were created using these methods.