Leakless end-to-end transport of small molecules through micron-length DNA nanochannels

Designed and engineered protein and DNA nanopores can be used to sense and characterize single molecules and control transmembrane transport of molecular species. However, designed biomolecular pores are less than 100 nm in length and are used primarily for transport across lipid membranes. Nanochannels that span longer distances could be used as conduits for molecules between nonadjacent compartments or cells. Here, we design micrometer-long, 7-nm-diameter DNA nanochannels that small molecules can traverse according to the laws of continuum diffusion. Binding DNA origami caps to channel ends eliminates transport and demonstrates that molecules diffuse from one channel end to the other rather than permeating through channel walls. These micrometer-length nanochannels can also grow, form interconnects, and interface with living cells. This work thus shows how to construct multifunctional, dynamic agents that control molecular transport, opening ways of studying intercellular signaling and modulating molecular transport between synthetic and living cells.

DNA origami frame filled with two types of single-stranded tiles

DNA origami and DNA single-stranded tiles (SSTs) are two basic motifs that are widely used in fabricating DNA nanostructures. Typically, DNA origami is self-folded via a long single phage strand (scaffold strand) and this process is aided by a myriad of short oligonucleotides (staple strand). Unlike DNA origami, SSTs construct nanostructures using many unique strands connected with each other to obtain specific shapes. These motifs are material- and labour-consuming, and require multiple different synthetic oligonucleotides, and DNA SSTs tend to remain kinetically trapped in the form of tubes. In this study, we present a new strategy that combines DNA origami with DNA SSTs to construct a DNA nanostructure with a predesigned shape. A rectangular DNA origami frame with ten dozen helper strands was filled with two types of SSTs assembled repeatedly, which avoided the kinetic trap and used fewer synthetic oligonucleotides. The assembly results were identified using atomic force microscopy. The experimental analysis demonstrated the stability and feasibility of the strategy.

Elucidating the Mechanical Energy for Cyclization of a DNA Origami Tile

DNA origami has emerged as a versatile method to synthesize nanostructures with high precision. This bottom-up self-assembly approach can produce not only complex static architectures, but also dynamic reconfigurable structures with tunable properties. While DNA origami has been explored increasingly for diverse applications, such as biomedical and biophysical tools, related mechanics are also under active investigation. Here we studied the structural properties of DNA origami and investigated the energy needed to deform the DNA structures. We used a single-layer rectangular DNA origami tile as a model system and studied its cyclization process. This origami tile was designed with an inherent twist by placing crossovers every 16 base-pairs (bp), corresponding to a helical pitch of 10.67 bp/turn, which is slightly different from that of native B-form DNA (~10.5 bp/turn). We used molecular dynamics (MD) simulations based on a coarse-grained model on an open-source computational platform, oxDNA. We calculated the energies needed to overcome the initial curvature and induce mechanical deformation by applying linear spring forces. We found that the initial curvature may be overcome gradually during cyclization and a total of ~33.1 kcal/mol is required to complete the deformation. These results provide insights into the DNA origami mechanics and should be useful for diverse applications such as adaptive reconfiguration and energy absorption.

Multiform DNA origami arrays using minimal logic control

Self-assembled DNA nanostructures significantly contribute to DNA nanotechnology. Algorithmic guiding of the assembly of DNA arrays remains a challenge in nanoarchitecture. Usually, the more sophisticated a DNA nanoarchitecture, the more DNA connections with specific sequences are required. This study aimed to investigate the feasibility of using the minimum pairs of DNA connection strands to implement algorithm-based self-assembly with finite DNA origamis. We found that the DNA origami linking complexity was markedly reduced. By rotating and turning the origami tile in different linking directions, we obtained 2 × 2 arrays of DNA origamis using a pair of DNA connections, 2 × 4 arrays using two pairs of DNA connections, and 4 × 4 arrays using three pairs of connection strands. We further analysed the effects of distortion on array formation. Overall, this study presents a hierarchical assembly strategy with minimal connections to generate multi-scale DNA arrays.

Adjusting Linking Strands to Form Size-Controllable DNA Origami Rings

DNA origami is a powerful tool in nanotechnology that can be used to construct arbitrary structures for several nanoengineering applications. Generally, the more complex and sophisticated the construction, the greater is the number of origamis and connection strands that will be needed. Therefore, developing an effective and low-cost method for multiform DNA architecture is important in nanoengineering. Here, we adopted an oblique linking strategy to connect cross-shaped DNA origami with a controlled curing angle. The size of the DNA rings ranged from four blocks of approximately 200 nm to eleven blocks of c.a. 600 nm. We observed that the minimum size of the DNA ring structure was limited by the width of a single block. The largest rings were negatively affected by thermodynamic randomness, and thus, DNA rings consisting of more than eleven blocks were not observed. This strategy facilitates the generation of various DNA origami rings, whose size can be controlled by adjusting the length of the connection strands.

An Aptamer-Nanotrain Assembled from Six-Letter DNA Delivers Doxorubicin Selectively to Liver Cancer Cells

Expanding the number of nucleotides in DNA increases the information density of functional DNA molecules, creating nanoassemblies that cannot be invaded by natural DNA/RNA in complex biological systems. Here, we show how six-letter GACTZP DNA contributes this property in two parts of a nanoassembly: 1) in an aptamer evolved from a six-letter DNA library to selectively bind liver cancer cells; and 2) in a six-letter self-assembling GACTZP nanotrain that carries the drug doxorubicin. The aptamer-nanotrain assembly, charged with doxorubicin, selectively kills liver cancer cells in culture, as the selectivity of the aptamer binding directs doxorubicin into the aptamer-targeted cells. The assembly does not kill untransformed cells that the aptamer does not bind. This architecture, built with an expanded genetic alphabet, is reminiscent of antibodies conjugated to drugs, which presumably act by this mechanism as well, but with the antibody replaced by an aptamer.

Multifunctional DNA Origami Nanoplatforms for Drug Delivery

DNA nanotechnology has been employed in the construction of self-assembled nano-biomaterials with uniform size and shape for various biological applications, such as bioimaging, diagnosis, or therapeutics. Herein, recent successful efforts to utilize multifunctional DNA origami nanoplatforms as drug-delivery vehicles are reviewed. Diagnostic and therapeutic strategies based on gold nanorods, chemotherapeutic drugs, cytosine-phosphate-guanine, functional proteins, gene drugs, and their combinations for optoacoustic imaging, photothermal therapy, chemotherapy, immunological therapy, gene therapy, and coagulation-based therapy are summarized. The challenges and opportunities for DNA-based nanocarriers for biological applications are also discussed.

Unprecedented Access to β-Arylated Selenophenes through Palladium-Catalysed Direct Arylation

Several reported methods allow access to α-arylated selenophenes, whereas the synthesis of β-arylated selenophenes remains very challenging. Here, the Pd-catalysed coupling of benzenesulfonyl chlorides with selenophenes affording regiospecific β-arylated selenophenes is reported. The reaction proceeds with easily accessible catalyst, base and substrates, and tolerates a variety of substituents both on the benzene and selenophene moieties. This transformation allows the programmed synthesis of polyarylated selenophenes with potential applications in pharmaceutical and materials chemistry, as the installation of aryl groups at the desired positions can be achieved.

Self-assembled silver nanoparticles in a bow-tie antenna configuration

The self-assembly of silver nanoparticles into a bow-tie antenna configuration is achieved with the DNA origami method. Instead of complicated particle geometries, spherical silver nanoparticles are used. Formation of the structures in high yields is verified with transmission electron microscopy and agarose gel electrophoresis. According to finite-difference time-domain simulations, the antenna configuration could be used as a DNA sensor.

Single-molecule analysis using DNA origami

During the last two decades, scientists have developed various methods that allow the detection and manipulation of single molecules, which have also been called "in singulo" approaches. Fundamental understanding of biochemical reactions, folding of biomolecules, and the screening of drugs were achieved by using these methods. Single-molecule analysis was also performed in the field of DNA nanotechnology, mainly by using atomic force microscopy. However, until recently, the approaches used commonly in nanotechnology adopted structures with a dimension of 10-20 nm, which is not suitable for many applications. The recent development of scaffolded DNA origami by Rothemund made it possible for the construction of larger defined assemblies. One of the most salient features of the origami method is the precise addressability of the structures formed: Each staple can serve as an attachment point for different kinds of nanoobjects. Thus, the method is suitable for the precise positioning of various functionalities and for the single-molecule analysis of many chemical and biochemical processes. Here we summarize recent progress in the area of single-molecule analysis using DNA origami and discuss the future directions of this research.