Defined-size DNA triple crossover construct for molecular electronics: modification, positioning and conductance properties

Hybrid Nanoassemblies from Viruses and DNA Nanostructures

Viruses are among the most intriguing nanostructures found in nature. Their atomically precise shapes and unique biological properties, especially in protecting and transferring genetic information, have enabled a plethora of biomedical applications. On the other hand, structural DNA nanotechnology has recently emerged as a highly useful tool to create programmable nanoscale structures. They can be extended to user defined devices to exhibit a wide range of static, as well as dynamic functions. In this review, we feature the recent development of virus-DNA hybrid materials. Such structures exhibit the best features of both worlds by combining the biological properties of viruses with the highly controlled assembly properties of DNA. We present how the DNA shapes can act as "structured" genomic material and direct the formation of virus capsid proteins or be encapsulated inside symmetrical capsids. Tobacco mosaic virus-DNA hybrids are discussed as the examples of dynamic systems and directed formation of conjugates. Finally, we highlight virus-mimicking approaches based on lipid- and protein-coated DNA structures that may elicit enhanced stability, immunocompatibility and delivery properties. This development also paves the way for DNA-based vaccines as the programmable nano-objects can be used for controlling immune cell activation.

Multifaceted aspects of charge transfer

Charge transfer and charge transport are by far among the most important processes for sustaining life on Earth and for making our modern ways of living possible. Involving multiple electron-transfer steps, photosynthesis and cellular respiration have been principally responsible for managing the energy flow in the biosphere of our planet since the Great Oxygen Event. It is impossible to imagine living organisms without charge transport mediated by ion channels, or electron and proton transfer mediated by redox enzymes. Concurrently, transfer and transport of electrons and holes drive the functionalities of electronic and photonic devices that are intricate for our lives. While fueling advances in engineering, charge-transfer science has established itself as an important independent field, originating from physical chemistry and chemical physics, focusing on paradigms from biology, and gaining momentum from solar-energy research. Here, we review the fundamental concepts of charge transfer, and outline its core role in a broad range of unrelated fields, such as medicine, environmental science, catalysis, electronics and photonics. The ubiquitous nature of dipoles, for example, sets demands on deepening the understanding of how localized electric fields affect charge transfer. Charge-transfer electrets, thus, prove important for advancing the field and for interfacing fundamental science with engineering. Synergy between the vastly different aspects of charge-transfer science sets the stage for the broad global impacts that the advances in this field have.

Evolution of Structural DNA Nanotechnology

The research field entitled structural DNA nanotechnology emerged in the beginning of the 1980s as the first immobile synthetic nucleic acid junctions were postulated and demonstrated. Since then, the field has taken huge leaps toward advanced applications, especially during the past decade. This Progress Report summarizes how the controllable, custom, and accurate nanostructures have recently evolved together with powerful design and simulation software. Simultaneously they have provided a significant expansion of the shape space of the nanostructures. Today, researchers can select the most suitable fabrication methods, and design paradigms and software from a variety of options when creating unique DNA nanoobjects and shapes for a plethora of implementations in materials science, optics, plasmonics, molecular patterning, and nanomedicine.

DNA nanostructure-directed assembly of metal nanoparticle superlattices

Structural DNA nanotechnology provides unique, well-controlled, versatile, and highly addressable motifs and templates for assembling materials at the nanoscale. These methods to build from the bottom-up using DNA as a construction material are based on programmable and fully predictable Watson-Crick base pairing. Researchers have adopted these techniques to an increasing extent for creating numerous DNA nanostructures for a variety of uses ranging from nanoelectronics to drug-delivery applications. Recently, an increasing effort has been put into attaching nanoparticles (the size range of 1-20 nm) to the accurate DNA motifs and into creating metallic nanostructures (typically 20-100 nm) using designer DNA nanoshapes as molds or stencils. By combining nanoparticles with the superior addressability of DNA-based scaffolds, it is possible to form well-ordered materials with intriguing and completely new optical, plasmonic, electronic, and magnetic properties. This focused review discusses the DNA structure-directed nanoparticle assemblies covering the wide range of different one-, two-, and three-dimensional systems.

Toward Single Electron Nanoelectronics Using Self-Assembled DNA Structure

DNA based structures offer an adaptable and robust way to develop customized nanostructures for various purposes in bionanotechnology. One main aim in this field is to develop a DNA nanobreadboard for a controllable attachment of nanoparticles or biomolecules to form specific nanoelectronic devices. Here we conjugate three gold nanoparticles on a defined size TX-tile assembly into a linear pattern to form nanometer scale isolated islands that could be utilized in a room temperature single electron transistor. To demonstrate this, conjugated structures were trapped using dielectrophoresis for current-voltage characterization. After trapping only high resistance behavior was observed. However, after extending the islands by chemical growth of gold, several structures exhibited Coulomb blockade behavior from 4.2 K up to room temperature, which gives a good indication that self-assembled DNA structures could be used for nanoelectronic patterning and single electron devices.

Metallic Nanostructures Based on DNA Nanoshapes

Metallic nanostructures have inspired extensive research over several decades, particularly within the field of nanoelectronics and increasingly in plasmonics. Due to the limitations of conventional lithography methods, the development of bottom-up fabricated metallic nanostructures has become more and more in demand. The remarkable development of DNA-based nanostructures has provided many successful methods and realizations for these needs, such as chemical DNA metallization via seeding or ionization, as well as DNA-guided lithography and casting of metallic nanoparticles by DNA molds. These methods offer high resolution, versatility and throughput and could enable the fabrication of arbitrarily-shaped structures with a 10-nm feature size, thus bringing novel applications into view. In this review, we cover the evolution of DNA-based metallic nanostructures, starting from the metallized double-stranded DNA for electronics and progress to sophisticated plasmonic structures based on DNA origami objects.

A modular DNA origami-based enzyme cascade nanoreactor

In this communication, we present a nanoscale reactor assembled from tuneable and spatially addressable tubular DNA origami units. We can controllably combine separate origami units equipped with glucose oxidase (GOx) and horseradish peroxidase (HRP), and demonstrate efficient GOx/HRP enzyme cascade reaction inside the tube. The reactor could be utilized as a nanoscale diagnostic tool, and modularity of the proposed system would further enable more complex reactions.

One-step large-scale deposition of salt-free DNA origami nanostructures

DNA origami nanostructures have tremendous potential to serve as versatile platforms in self-assembly -based nanofabrication and in highly parallel nanoscale patterning. However, uniform deposition and reliable anchoring of DNA nanostructures often requires specific conditions, such as pre-treatment of the chosen substrate or a fine-tuned salt concentration for the deposition buffer. In addition, currently available deposition techniques are suitable merely for small scales. In this article, we exploit a spray-coating technique in order to resolve the aforementioned issues in the deposition of different 2D and 3D DNA origami nanostructures. We show that purified DNA origamis can be controllably deposited on silicon and glass substrates by the proposed method. The results are verified using either atomic force microscopy or fluorescence microscopy depending on the shape of the DNA origami. DNA origamis are successfully deposited onto untreated substrates with surface coverage of about 4 objects/mm(2). Further, the DNA nanostructures maintain their shape even if the salt residues are removed from the DNA origami fabrication buffer after the folding procedure. We believe that the presented one-step spray-coating method will find use in various fields of material sciences, especially in the development of DNA biochips and in the fabrication of metamaterials and plasmonic devices through DNA metallisation.

Custom-shaped metal nanostructures based on DNA origami silhouettes

The DNA origami technique provides an intriguing possibility to develop customized nanostructures for various bionanotechnological purposes. One target is to create tailored bottom-up-based plasmonic devices and metamaterials based on DNA metallization or controlled attachment of nanoparticles to the DNA designs. In this article, we demonstrate an alternative approach: DNA origami nanoshapes can be utilized in creating accurate, uniform and entirely metallic (e.g. gold, silver and copper) nanostructures on silicon substrates. The technique is based on developing silhouettes of the origamis in the grown silicon dioxide layer, and subsequently using this layer as a mask for further patterning. The proposed method has a high spatial resolution, and the fabrication yields can approach 90%. The approach allows a cost-effective, parallel, large-scale patterning on a chip with fully tailored metallic nanostructures; the DNA origami shape and the applied metal can be specifically chosen for each conceivable implementation.

Plasmonic coupling and long-range transfer of an excitation along a DNA nanowire

We demonstrate an excitation transfer along a fluorescently labeled dsDNA nanowire over a length of several micrometers. Launching of the excitation is done by exciting a localized surface plasmon mode of a 40 nm silver nanoparticle by 800 nm femtosecond laser pulses via two-photon absorption. The plasmonic mode is subsequently coupled or transformed to excitation in the nanowire in contact with the particle and propagated along it, inducing bleaching of the dyes on its way. In situ as well as ex situ fluorescence microscopy is utilized to observe the phenomenon. In addition, transfer of the excitation along the nanowire to another nanoparticle over a separation of 5.7 μm was clearly observed. The nature of the excitation coupling and transfer could not be fully resolved here, but injection of an electron into the DNA from the excited nanoparticle and subsequent coupled transfer of charge (Dexter) and delocalized exciton (Frenkel) is the most probable mechanism. However, a direct plasmonic or optical coupling and energy transfer along the nanowire cannot be totally ruled out either. By further studies the observed phenomenon could be utilized in novel molecular systems, providing a long-needed communication method between molecular devices.

Growth of immobilized DNA by polymerase: bridging nanoelectrodes with individual dsDNA molecules

We present a method for controlled connection of gold electrodes with dsDNA molecules (locally on a chip) by utilizing polymerase to elongate single-stranded DNA primers attached to the electrodes. Thiol-modified oligonucleotides are directed and immobilized to nanoscale electrodes by means of dielectrophoretic trapping, and extended in a procedure mimicking PCR, finally forming a complete dsDNA molecule bridging the gap between the electrodes. The technique opens up opportunities for building from the bottom-up, for detection and sensing applications, and also for molecular electronics.