Preservation of DNA Nanostructure Carriers: Effects of Freeze-Thawing and Ionic Strength during Lyophilization and Storage

Delivering DNA Aptamers Across the Blood-Brain Barrier Reveals Heterogeneous Decreased ATP in Different Brain Regions of Alzheimer's Disease Mouse Models

DNA aptamers have been developed as sensors to detect metabolites with high sensitivity, selectivity, and biocompatibility. While they are effective in sensing important targets in the brain, the lack of methods for their efficient delivery across the blood-brain barrier (BBB) has significantly hindered their applications in brain research. To address this issue, we herein report the development of brain cell-derived exosomes as endogenous BBB delivery vehicles to deliver an ATP-responsive aptamer across the BBB of live mice for noninvasive live brain imaging. We found that the system uses endosome recycling to transfer the sensors between the delivered exosomes and native recycling endosomes, resulting in high delivery efficiencies. Using this system, we observed unique signal distributions for ATP across different brain regions, with significant accumulation in the subiculum and cortex in healthy mice. In an Alzheimer's disease transgenic mouse model, ATP levels decreased in the subiculum and cortex, demonstrating this method's capability to determine metabolite location and relative abundance with high spatial resolution in vivo. Since DNA aptamers have been obtained for many other targets, the method developed in this work can be applied to deliver sensors across the BBB to image a wide range of other brain-related metabolites.

Freezing Functional Nucleic Acids: From Molecular Reactions to Surface Immobilization

Biochemical reactions are typically slowed down by decreasing temperature. However, accelerated reaction kinetics have been observed for a long time. More recent examples have highlighted the unique role of freezing in fabricating supermaterials, degrading environmental contaminants, and accelerating bioreactions. Functional nucleic acids are DNA or RNA oligonucleotides with versatile properties, including target recognition, catalysis, and molecular co4mputing. In this review, we discuss the current observations and understanding of freezing-facilitated reactions involving functional nucleic acids. Molecular reactions such as ligation/conjugation, cleavage, and hybridization are discussed. Moreover, freezing-induced DNA-nanoparticle conjugations are introduced. Then, we describe our effect in immobilizing DNA on bulk surfaces. Finally, we address some critical questions and research opportunities in the field.

Enhancing Neuronal Cell Uptake of Therapeutic Nucleic Acids with Tetrahedral DNA Nanostructures

The successful translation of therapeutic nucleic acids (NAs) for the treatment of neurological disorders depends on their safe and efficient delivery to neural cells, in particular neurons. DNA nanostructures can be a promising NAs delivery vehicle. Nonetheless, the potential of DNA nanostructures for neuronal cell delivery of therapeutic NAs is unexplored. Here, tetrahedral DNA nanostructures (TDN) as siRNA delivery scaffolds to neuronal cells, exploring the influence of functionalization with two different reported neuronal targeting ligands: C4-3 RNA aptamer and Tet1 peptide are investigated. Nanostructures are characterized in vitro, as well as in silico using molecular dynamic simulations to better understand the overall TDN structural stability. Enhancement of neuronal cell uptake of TDN functionalized with the C4-3 Aptamer (TDN-Apt), not only in neuronal cell lines but also in primary neuronal cell cultures is demonstrated. Additionally, TDN and TDN-Apt nanostructures carrying siRNA are shown to promote silencing in a process aided by chloroquine-induced endosomal disruption. This work presents a thorough workflow for the structural and functional characterization of the proposed TDN as a nano-scaffold for neuronal delivery of therapeutic NAs and for targeting ligands evaluation, contributing to the future development of new neuronal drug delivery systems based on DNA nanostructures.

Automated Purification of DNA Origami with SPRI Beads

DNA origami synthesis is a well-established technique with wide-ranging applications. In most cases, the synthesized origami must be purified to remove excess materials such as DNA oligos and other functional molecules. While several purification techniques are routinely used, all have limitations, and cannot be integrated with robotic systems. Here the use of solid-phase reversible immobilization (SPRI) beads as a scalable, high-throughput, and automatable method to purify DNA origami is demonstrated. Not only can this method remove unreacted oligos and biomolecules with yields comparable to existing methods while maintaining the high structural integrity of the origami, but it can also be integrated into an automated workflow to purify simultaneously large numbers and quantities of samples. It is envisioned that the SPRI beads purification method will improve the scalability of DNA nanostructures synthesis both for research and commercial applications.

DNA nanostructure decoration: a how-to tutorial

DNA Nanotechnology is being applied to multiple research fields. The functionality of DNA nanostructures is significantly enhanced by decorating them with nanoscale moieties including: proteins, metallic nanoparticles, quantum dots, and chromophores. Decoration is a complex process and developing protocols for reliable attachment routinely requires extensive trial and error. Additionally, the granular nature of scientific communication makes it difficult to discern general principles in DNA nanostructure decoration. This tutorial is a guidebook designed to minimize experimental bottlenecks and avoid dead-ends for those wishing to decorate DNA nanostructures. We supplement the reference material on available technical tools and procedures with a conceptual framework required to make efficient and effective decisions in the lab. Together these resources should aid both the novice and the expert to develop and execute a rapid, reliable decoration protocols.

Data Storage Using DNA

The exponential growth of global data has outpaced the storage capacities of current technologies, necessitating innovative storage strategies. DNA, as a natural medium for preserving genetic information, has emerged as a highly promising candidate for next-generation storage medium. Storing data in DNA offers several advantages, including ultrahigh physical density and exceptional durability. Facilitated by significant advancements in various technologies, such as DNA synthesis, DNA sequencing, and DNA nanotechnology, remarkable progress has been made in the field of DNA data storage over the past decade. However, several challenges still need to be addressed to realize practical applications of DNA data storage. In this review, the processes and strategies of in vitro DNA data storage are first introduced, highlighting recent advancements. Next, a brief overview of in vivo DNA data storage is provided, with a focus on the various writing strategies developed to date. At last, the challenges encountered in each step of DNA data storage are summarized and promising techniques are discussed that hold great promise in overcoming these obstacles.

Processing DNA Storage through Programmable Assembly in a Droplet-Based Fluidics System

DNA can be used to store digital data, and synthetic short-sequence DNA pools are developed to store high quantities of digital data. However, synthetic DNA data cannot be actively processed in DNA pools. An active DNA data editing process is developed using splint ligation in a droplet-controlled fluidics (DCF) system. DNA fragments of discrete sizes (100-500 bps) are synthesized for droplet assembly, and programmed sequence information exchange occurred. The encoded DNA sequences are processed in series and parallel to synthesize the determined DNA pools, enabling random access using polymerase chain reaction amplification. The sequencing results of the assembled DNA data pools can be orderly aligned for decoding and have high fidelity through address primer scanning. Furthermore, eight 90 bps DNA pools with pixel information (png: 0.27-0.28 kB), encoded by codons, are synthesized to create eight 270 bps DNA pools with an animation movie chip file (mp4: 12 kB) in the DCF system.

Superstructure-dependent stability of DNA origami nanostructures in the presence of chaotropic denaturants

The structural stability of DNA origami nanostructures in various chemical environments is an important factor in numerous applications, ranging from biomedicine and biophysics to analytical chemistry and materials synthesis. In this work, the stability of six different 2D and 3D DNA origami nanostructures is assessed in the presence of three different chaotropic salts, i.e., guanidinium sulfate (Gdm2SO4), guanidinium chloride (GdmCl), and tetrapropylammonium chloride (TPACl), which are widely employed denaturants. Using atomic force microscopy (AFM) to quantify nanostructural integrity, Gdm2SO4 is found to be the weakest and TPACl the strongest DNA origami denaturant, respectively. Despite different mechanisms of actions of the selected salts, DNA origami stability in each environment is observed to depend on DNA origami superstructure. This is especially pronounced for 3D DNA origami nanostructures, where mechanically more flexible designs show higher stability in both GdmCl and TPACl than more rigid ones. This is particularly remarkable as this general dependence has previously been observed under Mg2+-free conditions and may provide the possibility to optimize DNA origami design toward maximum stability in diverse chemical environments. Finally, it is demonstrated that melting temperature measurements may overestimate the stability of certain DNA origami nanostructures in certain chemical environments, so that such investigations should always be complemented by microscopic assessments of nanostructure integrity.

Lyophilization Reduces Aggregation of Three-Dimensional DNA Origami at High Concentrations

Although for many purposes, low concentrations of DNA origami are sufficient, certain applications such as cryo electron microscopy, measurements involving small-angle X-ray scattering, or in vivo applications require high DNA origami concentrations of >200 nM. This is achievable by ultrafiltration or polyethylene glycol precipitation but often at the expense of increasing structural aggregation due to prolonged centrifugation and final redispersion in low buffer volumes. Here, we show that lyophilization and subsequent redispersion in low buffer volumes can achieve high concentrations of DNA origami while drastically reducing aggregation due to initially very low DNA origami concentrations in low salt buffers. We demonstrate this for four structurally different types of three-dimensional DNA origami. All of these structures exhibit different aggregation behaviors at high concentrations (tip-to-tip stacking, side-to-side binding, or structural interlocking), which can be drastically reduced by dispersion in larger volumes of a low salt buffer and subsequent lyophilization. Finally, we show that this procedure can also be applied to silicified DNA origami to achieve high concentrations with low aggregation. We thus find that lyophilization is not only a tool for long-term storage of biomolecules but also an excellent way for up-concentrating while maintaining well-dispersed solutions of DNA origami.

Hierarchical integration of DNA nanostructures and NanoGold onto a microchip facilitates covalent chemistry-mediated purification of circulating tumor cells in head and neck squamous cell carcinoma

It is well-established that the combined use of nanostructured substrates and immunoaffinity agents can enhance the cell-capture performance of the substrates, thus offering a practical solution to effectively capture circulating tumor cells (CTCs) in peripheral blood. Developing along this strategy, this study first demonstrated a top-down approach for the fabrication of tetrahedral DNA nanostructure (TDN)-NanoGold substrates through the hierarchical integration of three functional constituents at various length-scales: a macroscale glass slide, sub-microscale self-organized NanoGold, and nanoscale self-assembled TDN. The TDN-NanoGold substrates were then assembled with microfluidic chaotic mixers to give TDN-NanoGold Click Chips. In conjunction with the use of copper (Cu)-catalyzed azide-alkyne cycloaddition (CuAAC)-mediated CTC capture and restriction enzyme-triggered CTC release, TDN-NanoGold Click Chips allow for effective enumeration and purification of CTCs with intact cell morphologies and preserved molecular integrity. To evaluate the clinical utility of TDN-NanoGold Click Chips, we used these devices to isolate and purify CTCs from patients with human papillomavirus (HPV)-positive (+) head and neck squamous cell carcinoma (HNSCC). The purified HPV(+) HNSCC CTCs were then subjected to RT-ddPCR testing, allowing for detection of E6/E7 oncogenes, the characteristic molecular signatures of HPV(+) HNSCC. We found that the resulting HPV(+) HNSCC CTC counts and E6/E7 transcript copy numbers are correlated with the treatment responses in the patients, suggesting the potential clinical utility of TDN-NanoGold Click Chips for non-invasive diagnostic applications of HPV(+) HNSCC.

Metal-Organic Frameworks in Microfluidics Enable Fast Encapsulation/Extraction of DNA for Automated and Integrated Data Storage

DNA as an exceptional data storage medium offers high information density. However, DNA storage requires specialized equipment and tightly controlled environments for storage. Fast encapsulation within minutes for enhanced DNA stability to do away with specialized equipment and fast DNA extraction remain a challenge. Here, we report a DNA microlibrary that can be encapsulated by metal-organic frameworks (MOFs) within 10 min and extracted (5 min) in a single microfluidic chip for automated and integrated DNA-based data storage. The DNA microlibrary@MOFs enhances the stability of data-encoded DNA against harsh environments. The encoded information can be read out perfectly after accelerated aging, equivalent to being readable after 10 years of storage at 25 °C, 50% relative humidity, and 10 000 lx sunlight radiation. Moreover, the library enables fast retrieval of target data via flow cytometry and can be reproduced after each access.

Uptake and stability of DNA nanostructures in cells: a cross-sectional overview of the current state of the art

The physical and chemical properties of synthetic DNA have transformed this prototypical biopolymer into a versatile nanoscale building block material in the form of DNA nanotechnology. DNA nanotechnology is, in turn, providing unprecedented precision bioengineering for numerous biomedical applications at the nanoscale including next generation immune-modulatory materials, vectors for targeted delivery of nucleic acids, drugs, and contrast agents, intelligent sensors for diagnostics, and theranostics, which combines several of these functionalities into a single construct. Assembling a DNA nanostructure to be programmed with a specific number of targeting moieties on its surface to imbue it with concomitant cellular uptake and retention capabilities along with carrying a specific therapeutic dose is now eminently feasible due to the extraordinary self-assembling properties and high formation efficiency of these materials. However, what remains still only partially addressed is how exactly this class of materials is taken up into cells in both the native state and as targeted or chemically facilitated, along with how stable they are inside the cellular cytosol and other cellular organelles. In this minireview, we summarize what is currently reported in the literature about how (i) DNA nanostructures are taken up into cells along with (ii) what is understood about their subsequent stability in the complex multi-organelle environment of the cellular milieu along with biological fluids in general. This allows us to highlight the many challenges that still remain to overcome in understanding DNA nanostructure-cellular interactions in order to fully translate these exciting new materials.

Time-Dependent DNA Origami Denaturation by Guanidinium Chloride, Guanidinium Sulfate, and Guanidinium Thiocyanate

Guanidinium (Gdm) undergoes interactions with both hydrophilic and hydrophobic groups and, thus, is a highly potent denaturant of biomolecular structure. However, our molecular understanding of the interaction of Gdm with proteins and DNA is still rather limited. Here, we investigated the denaturation of DNA origami nanostructures by three Gdm salts, i.e., guanidinium chloride (GdmCl), guanidinium sulfate (Gdm₂SO₄), and guanidinium thiocyanate (GdmSCN), at different temperatures and in dependence of incubation time. Using DNA origami nanostructures as sensors that translate small molecular transitions into nanostructural changes, the denaturing effects of the Gdm salts were directly visualized by atomic force microscopy. GdmSCN was the most potent DNA denaturant, which caused complete DNA origami denaturation at 50 °C already at a concentration of 2 M. Under such harsh conditions, denaturation occurred within the first 15 min of Gdm exposure, whereas much slower kinetics were observed for the more weakly denaturing salt Gdm₂SO₄ at 25 °C. Lastly, we observed a novel non-monotonous temperature dependence of DNA origami denaturation in Gdm₂SO₄ with the fraction of intact nanostructures having an intermediate minimum at about 40 °C. Our results, thus, provide further insights into the highly complex Gdm–DNA interaction and underscore the importance of the counteranion species.

Anion-specific structure and stability of guanidinium-bound DNA origami

While the folding of DNA into rationally designed DNA origami nanostructures has been studied extensively with the aim of increasing structural diversity and introducing functionality, the fundamental physical and chemical properties of these nanostructures remain largely elusive. Here, we investigate the correlation between atomistic, molecular, nanoscopic, and thermodynamic properties of DNA origami triangles. Using guanidinium (Gdm) as a DNA-stabilizing but potentially also denaturing cation, we explore the dependence of DNA origami stability on the identity of the accompanying anions. The statistical analyses of atomic force microscopy (AFM) images and circular dichroism (CD) spectra reveals that sulfate and chloride exert stabilizing and destabilizing effects, respectively, already below the global melting temperature of the DNA origami triangles. We identify structural transitions during thermal denaturation and show that heat capacity changes ΔC_p determine the temperature sensitivity of structural damage. The different hydration shells of the anions and their potential to form Gdm⁺ ion pairs in concentrated salt solutions modulate ΔC_p by altered wetting properties of hydrophobic DNA surface regions as shown by molecular dynamics simulations. The underlying structural changes on the molecular scale become amplified by the large number of structurally coupled DNA segments and thereby find nanoscopic correlations in AFM images.

Characterization of DNA nanostructure stability by size exclusion chromatography

DNA-based nanostructures (DNs) are advantageous for the design of functional materials for biology and medicine due to the nanoscale control provided by their predictable self-assembly. However, the use of DNs in vivo has been limited due to structural instability in biofluids. As the stability of a particular DN sets the scope of its potential biological applications, efficient methods to characterize stability are required. Here, we apply size exclusion chromatography (SEC) to study the stability of a tetrahedron DNA nanostructure (TDN) and demonstrate the analytical capabilities of our method in characterizing degradation by enzymes and a diluted human serum matrix. We show that SEC analysis can reliably assay TDN degradation by a nuclease through direct injection and peak integration. Furthermore, data analysis using a ratio chromatogram technique enables TDN peak deconvolution from the matrix of serum proteins. Using our method, we found that TDNs exhibit half-lives of 23.9 hours and 10.1 hours in 20% and 50% diluted human serum, respectively, which is consistent with reported stability studies in 10% fetal bovine serum. We anticipate that this method can be broadly applicable to characterize a variety of DNs and serve as an efficient technique toward analysis of the stability of new DN designs in complex biological matrixes.

Smart Drug Delivery Systems Based on DNA Nanotechnology

The development of DNA nanotechnology has attracted tremendous attention in biotechnological and biomedical fields involving biosensing, bioimaging and disease therapy. In particular, precise control over size and shape, easy modification, excellent programmability and inherent homology make the sophisticated DNA nanostructures vital for constructing intelligent drug carriers. Recent advances in the design of multifunctional DNA-based drug delivery systems (DDSs) have demonstrated the effectiveness and advantages of DNA nanostructures, showing the unique benefits and great potential in enhancing the delivery of pharmaceutical compounds and reducing systemic toxicity. This Review aims to overview the latest researches on DNA nanotechnology-enabled nanomedicine and give a perspective on their future opportunities.

DNA Origami-Enabled Biosensors

Biosensors are small but smart devices responding to the external stimulus, widely used in many fields including clinical diagnosis, healthcare and environment monitoring, etc. Moreover, there is still a pressing need to fabricate sensitive, stable, reliable sensors at present. DNA origami technology is able to not only construct arbitrary shapes in two/three dimension but also control the arrangement of molecules with different functionalities precisely. The functionalization of DNA origami nanostructure endows the sensing system potential of filling in weak spots in traditional DNA-based biosensor. Herein, we mainly review the construction and sensing mechanisms of sensing platforms based on DNA origami nanostructure according to different signal output strategies. It will offer guidance for the application of DNA origami structures functionalized by other materials. We also point out some promising directions for improving performance of biosensors.

Gene Therapy Based on Nucleic Acid Nanostructure

During the past decades, nucleic acids have been employed for the construction of versatile nanostructures with well-defined shapes and sizes. Owing to the remarkable programmability, addressability, and biocompatibility, nucleic acid nanostructures are extensively applied in biomedical researches, such as bioimaging, biosensing, and drug delivery. In particular, nucleic acid nanostructures can act as promising candidates for the delivery of gene-related nucleic acid drugs based on the inherent homology. In this review, the recent progress in the design of multifunctional nucleic acid nanocarriers for gene therapy through antisense, RNA interference, gene editing, and gene expression is summarized. Furthermore, the challenges and future opportunities of nucleic acid nanotechnology in biomedical applications will be discussed.

Challenges and Perspectives of DNA Nanostructures in Biomedicine

DNA nanotechnology holds substantial promise for future biomedical engineering and the development of novel therapies and diagnostic assays. The subnanometer-level addressability of DNA nanostructures allows for their precise and tailored modification with numerous chemical and biological entities, which makes them fit to serve as accurate diagnostic tools and multifunctional carriers for targeted drug delivery. The absolute control over shape, size, and function enables the fabrication of tailored and dynamic devices, such as DNA nanorobots that can execute programmed tasks and react to various external stimuli. Even though several studies have demonstrated the successful operation of various biomedical DNA nanostructures both in vitro and in vivo, major obstacles remain on the path to real-world applications of DNA-based nanomedicine. Here, we summarize the current status of the field and the main implementations of biomedical DNA nanostructures. In particular, we focus on open challenges and untackled issues and discuss possible solutions.

Nanopore-Based DNA Hard Drives for Rewritable and Secure Data Storage

Nanopores are powerful single-molecule tools for label-free sensing of nanoscale molecules including DNA that can be used for building designed nanostructures and performing computations. Here, DNA hard drives (DNA-HDs) are introduced based on DNA nanotechnology and nanopore sensing as a rewritable molecular memory system, allowing for storing, operating, and reading data in the changeable three-dimensional structure of DNA. Writing and erasing data are significantly improved compared to previous molecular storage systems by employing controllable attachment and removal of molecules on a long double-stranded DNA. Data reading is achieved by detecting the single molecules at the millisecond time scale using nanopores. The DNA-HD also ensures secure data storage where the data can only be read after providing the correct physical molecular keys. Our approach allows for easy-writing and easy-reading, rewritable, and secure data storage toward a promising miniature scale integration for molecular data storage and computation.

Cryopreservation of DNA Origami Nanostructures

Although DNA origami nanostructures have found their way into numerous fields of fundamental and applied research, they often suffer from rather limited stability when subjected to environments that differ from the employed assembly conditions, that is, suspended in Mg²⁺ -containing buffer at moderate temperatures. Here, means for efficient cryopreservation of 2D and 3D DNA origami nanostructures and, in particular, the effect of repeated freezing and thawing cycles are investigated. It is found that, while the 2D DNA origami nanostructures maintain their structural integrity over at least 32 freeze-thaw cycles, ice crystal formation makes the DNA origami gradually more sensitive toward harsh sample treatment conditions. Whereas no freeze damage could be detected in 3D DNA origami nanostructures subjected to 32 freeze-thaw cycles, 1000 freeze-thaw cycles result in significant fragmentation. The cryoprotectants glycerol and trehalose are found to efficiently protect the DNA origami nanostructures against freeze damage at concentrations between 0.2 × 10^-3 and 200 × 10^-3 m and without any negative effects on DNA origami shape. This work thus provides a basis for the long-term storage of DNA origami nanostructures, which is an important prerequisite for various technological and medical applications.

Aptamer-Functionalized DNA Nanostructures for Biological Applications

DNA nanostructures hold great promise for various applications due to their remarkable properties, including programmable assembly, nanometric positional precision, and dynamic structural control. The past few decades have seen the development of various kinds of DNA nanostructures that can be employed as useful tools in fields such as chemistry, materials, biology, and medicine. Aptamers are short single-stranded nucleic acids that bind to specific targets with excellent selectivity and high affinity and play critical roles in molecular recognition. Recently, many attempts have been made to integrate aptamers with DNA nanostructures for a range of biological applications. This review starts with an introduction to the features of aptamer-functionalized DNA nanostructures. The discussion then focuses on recent progress (particularly during the last five years) in the applications of these nanostructures in areas such as biosensing, bioimaging, cancer therapy, and biophysics. Finally, challenges involved in the practical application of aptamer-functionalized DNA nanostructures are discussed, and perspectives on future directions for research into and applications of aptamer-functionalized DNA nanostructures are provided.

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.