Ultrafast reversible photo-cross-linking reaction: toward in situ DNA manipulation

Light Responsive DNA Nanomaterials and Their Biomedical Applications

DNA nanomaterials have been widely employed for various biomedical applications. With rapid development of chemical modification of nucleic acid, serials of stimuli-responsive elements are included in the multifunctional DNA nanomaterials. In this review, we summarize the recent advances in light responsive DNA nanomaterials based on photocleavage/photodecage, photoisomerization, and photocrosslinking for efficient bioimaging (including imaging of small molecule, microRNA, and protein) and drug delivery (including delivery of small molecule, nucleic acid, and gene editing system). We also discuss the remaining challenges and future perspectives of the light responsive DNA nanomaterials in biomedical applications.

Collective Molecular Machines: Multidimensionality and Reconfigurability

Molecular machines are key to cellular activity where they are involved in converting chemical and light energy into efficient mechanical work. During the last 60 years, designing molecular structures capable of generating unidirectional mechanical motion at the nanoscale has been the topic of intense research. Effective progress has been made, attributed to advances in various fields such as supramolecular chemistry, biology and nanotechnology, and informatics. However, individual molecular machines are only capable of producing nanometer work and generally have only a single functionality. In order to address these problems, collective behaviors realized by integrating several or more of these individual mechanical units in space and time have become a new paradigm. In this review, we comprehensively discuss recent developments in the collective behaviors of molecular machines. In particular, collective behavior is divided into two paradigms. One is the appropriate integration of molecular machines to efficiently amplify molecular motions and deformations to construct novel functional materials. The other is the construction of swarming modes at the supramolecular level to perform nanoscale or microscale operations. We discuss design strategies for both modes and focus on the modulation of features and properties. Subsequently, in order to address existing challenges, the idea of transferring experience gained in the field of micro/nano robotics is presented, offering prospects for future developments in the collective behavior of molecular machines.

UltraFast PhotoInduced double duplex DNA invasion into a 400-mer dsDNA target

BACKGROUND

Natural DNA restriction enzymes bind duplex DNA with high affinity at multiple sites; however, for some of the artificial chemical-based restriction moieties, invasion of the double-strand for efficient cleavage is an obstacle. We have previously reported photo-induced double-duplex invasion (pDDI) using 3-cyanovinylcarbazole (K)-containing probes for both the target strands that photo-crosslink with pyrimidine bases in a sequence-specific manner on both the strands, stabilizing the opened double-strand for cleavage. The drawback of the pDDI was low efficiency due to inter-probe cross-linking, solved by the inclusion of 5-cyano-uridine at -1 position on the complimentary strand with respect to K in both probes. Although this led to reduced inter-probe cross-linking, the pDDI efficiency was still low.

RESULTS

Here, we report that inter-probe cross-linking and intra-probe cross-linking of a single probe is also leading to reduced pDDI efficiency. We addressed this problem by designing DDI probes to inhibit both inter-probe and intra-probe cross-linking.

CONCLUSION

Based on the new design of pDDI probe with 5-cyano uridine led to a drastic increase in the efficiency of pDDI in (400-mer) double-stranded DNA with only 1 s of photo-irradiation.

Toward three-dimensional DNA industrial nanorobots

Nanoscale industrial robots have potential as manufacturing platforms and are capable of automatically performing repetitive tasks to handle and produce nanomaterials with consistent precision and accuracy. We demonstrate a DNA industrial nanorobot that fabricates a three-dimensional (3D), optically active chiral structure from optically inactive parts. By making use of externally controlled temperature and ultraviolet (UV) light, our programmable robot, ~100 nanometers in size, grabs different parts, positions and aligns them so that they can be welded, releases the construct, and returns to its original configuration ready for its next operation. Our robot can also self-replicate its 3D structure and functions, surpassing single-step templating (restricted to two dimensions) by using folding to access the third dimension and more degrees of freedom. Our introduction of multiple-axis precise folding and positioning as a tool/technology for nanomanufacturing will open the door to more complex and useful nano- and microdevices.

Furan-based (photo)oxidation reactions and their application in nucleic acid and protein targeting

Oligonucleotides (ODNs) find applications as diagnostic and therapeutic tools due to their unique ability to interact, thanks to Watson-Crick base pairing, with a specific DNA or RNA target strand. Although most of the tools available today rely on mere hydrogen bond formation, chemical modifications to enable covalent interstrand-crosslinking (ICL) have been reported, and are gaining a place under the spotlight as they potentially offer a series of advantages over the state of the art, including a higher potency and selectivity. This methodological paper focuses on the use of a pro-reactive furan moiety and its subsequent oxidation for applications in ODN targeting. The design of effective capture and targeting probes to ensure high ICL yields is discussed and the mechanisms underlying the (photo)chemical oxidation of furan are explained. Furthermore, examples of furan-containing DNAs designed for different applications, including DNA-DNA or DNA-RNA ICL and DNA-peptide/protein targeting, are provided. The paper highlights the advantages of using different oxidative chemical triggers, such as N-bromosuccinimide or singlet oxygen, to offer additional selectivity control over the ICL reaction.

Acceleration of the Deamination of Cytosine through Photo-Crosslinking

Herein, we report the major factor for deamination reaction rate acceleration, i.e., hydrophilicity, by using various 5-substituted target cytosines and by carrying out deamination at high temperatures. Through substitution of the groups at the 5'-position of the cytosine, the effect of hydrophilicity was understood. It was then used to compare the various modifications of the photo-cross-linkable moiety as well as the effect of the counter base of the cytosine to edit both DNA and RNA. Furthermore, we were able to achieve cytosine deamination at 37 °C with a half-life in the order of a few hours.

Programmable DNA Interstrand Crosslinking by Alkene-Alkyne [2 + 2] Photocycloaddition

Covalent crosslinking of DNA strands provides a useful tool for medical, biochemical, and DNA nanotechnology applications. Here we present a light-induced interstrand DNA crosslinking reaction using the modified nucleoside 5-phenylethynyl-2'-deoxyuridine (^PhedU). The crosslinking ability of ^PhedU was programmed by base pairing and by metal ion interaction at the Watson-Crick base pairing site. Rotation to intrahelical positions was favored by hydrophobic stacking and enabled an unexpected photochemical alkene-alkyne [2 + 2] cycloaddition within the DNA duplex, resulting in efficient formation of a ^PhedU dimer after short irradiation times of a few seconds. A ^PhedU-dimer-containing DNA was shown to efficiently bind a helicase complex, but the covalent crosslink completely prevented DNA unwinding, suggesting possible applications in biochemistry or structural biology.

Supernatural: Artificial Nucleobases and Backbones to Program Hybridization-Based Assemblies and Circuits

The specificity and predictability of hybridization make oligonucleotides a powerful platform to program assemblies and networks with logic-gated responses, an area of research which has grown into a field of its own. While the field has capitalized on the commercial availability of DNA oligomers with its four canonical nucleobases, there are opportunities to extend the capabilities of the hardware with unnatural nucleobases and other backbones. This Topical Review highlights nucleobases that favor hybridizations that are empowering for assemblies and networks as well as two chiral XNAs than enable orthogonal hybridization networks.

Progresses in Cell-Free In Vitro Evolution

Biopolymers, such as proteins and RNA, are integral components of living organisms and have evolved through a process of repeated mutation and selection. The technique of "cell-free in vitro evolution" is a powerful experimental approach for developing biopolymers with desired functions and structural properties. Since Spiegelman's pioneering work over 50 years ago, biopolymers with a wide range of functions have been developed using in vitro evolution in cell-free systems. The use of cell-free systems offers several advantages, including the ability to synthesize a wider range of proteins without the limitations imposed by cytotoxicity, and the capacity for higher throughput and larger library sizes than cell-based evolutionary experiments. In this chapter, we provide a comprehensive overview of the progress made in the field of cell-free in vitro evolution by categorizing evolution into directed and undirected. The biopolymers produced by these methods are valuable assets in medicine and industry, and as a means of exploring the potential of biopolymers.

A novel agonist with homobivalent single-domain antibodies that bind the FGF receptor 1 domain III functions as an FGF2 ligand

Fibroblast growth factor (FGF) is a multifunctional protein that exhibits a wide range of biological effects. Most commonly, it acts as a mitogen, but it also has regulatory, morphological, and endocrine effects. The four receptor subtypes of FGF are activated by more than 20 different FGF ligands. FGF2, one of the FGF ligands, is an essential factor for cell culture in stem cells for regenerative medicine; however, recombinant FGF2 is extremely unstable. Here, we successfully generated homobivalent agonistic single-domain antibodies (variable domain of heavy chain of heavy chain antibodies referred to as VHHs) that bind to domain III and induce activation of the FGF receptor 1 and thus transduce intracellular signaling. This agonistic VHH has similar biological activity (EC₅₀) as the natural FGF2 ligand. Furthermore, we determined that the agonistic VHH could support the proliferation of human-induced pluripotent stem cells (PSCs) and human mesenchymal stem cells, which are PSCs for regenerative medicine. In addition, the agonistic VHH could maintain the ability of mesenchymal stem cells to differentiate into adipocytes or osteocytes, indicating that it could maintain the properties of PSCs. These results suggest that the VHH agonist may function as an FGF2 mimetic in cell preparation of stem cells for regenerative medicine with better cost effectiveness.

DNA-functionalized colloidal crystals for macromolecular encapsulation

Novel DNA-based structures with the ability to encapsulate nanoscale molecules, such as proteins, can be applied to a wide range of areas, including reaction fields and micro/nano drug carriers. DNA-functionalized nanoparticle (DNA-NP) colloidal crystals have emerged as a new class of programmable DNA-based structures harboring metal nanoparticles with improved mechanical properties. The encapsulation of guest molecules into empty spaces in lattice structures is theoretically possible. However, due to the lack of a strategy for versatile encapsulation of guest molecules, the feasibility of nanoscale encapsulation by DNA-NP crystals is unclear. In this study, we developed DNA-functionalized gold nanoparticle (DNA-AuNP) crystals with tunable interparticle spacing for molecular encapsulation. We demonstrated that the modification of DNA-AuNP crystals with functional moieties, that is, biotin molecules, was effective in retaining molecules in the crystals. The crystallinities before and after encapsulation of the molecules were confirmed using small-angle X-ray scattering. We also succeeded in encapsulating CRISPR/Cas9 ribonucleoproteins into DNA-AuNP crystals by harnessing their affinity for target molecules. These findings demonstrated the potential use of metal-DNA hybrid crystals as carriers for direct protein delivery via biolistic bombardment. Thus, this study provides an attractive strategy for creating a new class of DNA-based structures for macromolecular encapsulation, and an alternative research direction toward colloidal crystal engineering using DNA.

Photo-Reactivity of Binaphthalene Triphenylphosphonium Salts: DNA Interstrand Cross-Link Formation and Substituent Effects

Five novel 1,1'-binaphthalene analogues 1a-1e with triphenylphosphonium (TPP⁺) salts as a leaving group have been synthesized and characterized as photo-activatable DNA alkylating agents. Phototriggered release of the TPP⁺ group from 1a-1e generated naphthalenylmethyl-free radicals that were spontaneously transformed to the corresponding cations directly producing DNA interstrand cross-link (ICL) formation via alkylation. The substituents at position 4 not only affect the efficiency of ICL formation but also influence the reaction rate for DNA cross-linking. Groups with small or medium size favor ICL formation, while a bulky substituent (e.g., phenyl group) prevents DNA interstrand cross-linking. DNA alkylation by the naphthalenylmethyl cations photo-generated from 1a-1e occurs at dG, dC, and dA, while interstrand cross-linking took place with dG/dC base pairs. The TPP⁺ salts (1a-1e) are cations with both lipophilic and hydrophilic properties, which have great potential for biological applications.

Pre-PCR Mutation-Enrichment Methods for Liquid Biopsy Applications

Liquid biopsy is having a remarkable impact on healthcare- and disease-management in the context of personalized medicine. Circulating free DNA (cfDNA) is one of the most instructive liquid-biopsy-based biomarkers and harbors valuable information for diagnostic, predictive, and prognostic purposes. When it comes to cancer, circulating DNA from the tumor (ctDNA) has a wide range of applications, from early cancer detection to the early detection of relapse or drug resistance, and the tracking of the dynamic genomic make-up of tumor cells. However, the detection of ctDNA remains technically challenging, due, in part, to the low frequency of ctDNA among excessive circulating cfDNA originating from normal tissues. During the past three decades, mutation-enrichment methods have emerged to boost sensitivity and enable facile detection of low-level mutations. Although most developed techniques apply mutation enrichment during or following initial PCR, there are a few techniques that allow mutation selection prior to PCR, which provides advantages. Pre-PCR enrichment techniques can be directly applied to genomic DNA and diminish the influence of PCR errors that can take place during amplification. Moreover, they have the capability for high multiplexity and can be followed by established mutation detection and enrichment technologies without changes to their established procedures. The first approaches for pre-PCR enrichment were developed by employing restriction endonucleases directly on genomic DNA in the early 1990s. However, newly developed pre-PCR enrichment methods provide higher sensitivity and versatility. This review describes the available pre-PCR enrichment methods and focuses on the most recently developed techniques (NaME-PrO, UVME, and DEASH/MAESTRO), emphasizing their applications in liquid biopsies.

Hybridization-specific chemical reactions to create interstrand crosslinking and threaded structures of nucleic acids

The interstrand crosslinking and threaded structures of nucleic acids have high potential in oligonucleotide therapeutics, chemical biology, and nanotechnology. For example, properly designed crosslinking structures provide high activity and nuclease resistance for anti-miRNAs. The noncovalent labeling and modification by the threaded structures are useful as new chemical biology tools. Photoreversible crosslinking creates smart materials, such as reversible photoresponsive gels and DNA origami objects. This review introduces the creation of interstrand crosslinking and threaded structures, such as catenanes and rotaxanes, based on hybridization-specific chemical reactions and their functions and perspectives.

Lipid bilayer-assisted dynamic self-assembly of hexagonal DNA origami blocks into monolayer crystalline structures with designed geometries

The DNA origami technique is used to construct custom-shaped nanostructures that can be used as components of two-dimensional crystalline structures with user-defined structural patterns. Here, we designed an Mg²⁺-responsive hexagonal 3D DNA origami block with self-shape-complementary ruggedness on the sides. Hexagonal DNA origami blocks were electrostatically adsorbed onto a fluidic lipid bilayer membrane surface to ensure lateral diffusion. A subsequent increase in the Mg²⁺ concentration in the surrounding environment induced the self-assembly of the origami blocks into lattices with prescribed geometries based on a self-complementary shape fit. High-speed atomic force microscopy (HS-AFM) images revealed dynamic events involved in the self-assembly process, including edge reorganization, defect splitting, diffusion, and filling, which provide a glimpse into how the lattice structures are self-improved.

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Lipid bilayer-assisted self-assembly of 3D DNA origami blocks was achieved

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Time-lapse AFM imaging of the self-assembly processes was performed

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Different assembly patterns were achieved from a single DNA origami design

Photo-Cross-Linked Probe-Modified Magnetic Particles for the Selective and Reliable Recovery of Nucleic Acids

Polymerase chain reaction (PCR) assays are used to diagnose various infectious diseases such as Coronavirus disease 2019 by detecting the nucleic acids of the pathogen. However, in practice, the yield of the extraction process and the inhibition of the reverse transcription reaction and PCR by foreign substances reduce the sensitivity and may yield false negative results. The sensitivity of the PCR test can be improved by using technologies that can reliably capture the target nucleic acid and remove foreign substances. In this study, we developed photo-cross-linkable probe-modified magnetic particles (PPMPs) for the sequence-specific recovery of target nucleic acids using photo-cross-linkable artificial nucleic acid probes and magnetic particles. Nucleic acid probes modified with photo-cross-linkable artificial nucleic acids can hybridize with the target nucleic acids in a sequence-specific manner and then securely capture the target nucleic acids by UV irradiation-mediated covalent bonding. Then the target nucleic acid is detected by trapping the target-bound probe on the surface of the magnetic particles and subjecting these collected magnetic particles to PCR. Recovery of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) N gene pseudo-DNA (120 bp) was performed using PPMPs. We confirmed that the PPMPs captured the target consistently even after washes were done with denaturing agents and surfactants. Even in the presence of foreign DNA fragments, PPMPs were able to specifically recover the target DNA. This method allows for a more accurate detection by recovering only the target DNA for PCR. Hence, PPMPs can be successfully used for PCR-mediated detection of SARS-CoV-2 and other pathogens whose nucleic acid sequences are known.

Sequence-Specific Recognition of Double-Stranded DNA by Peptide Nucleic Acid Forming Double-Duplex Invasion Complex

Peptide nucleic acid (PNA) is an analog of natural nucleic acids, where the sugar-phosphate backbone of DNA is replaced by an electrostatically neutral N-(2-aminoethyl)glycine backbone. This unique peptide-based backbone enables PNAs to form a very stable duplex with the complementary nucleic acids via Watson–Crick base pairing since there is no electrostatic repulsion between PNA and DNA·RNA. With this high nucleic acid affinity, PNAs have been used in a wide range of fields, from biological applications such as gene targeting, to engineering applications such as probe and sensor developments. In addition to single-stranded DNA, PNA can also recognize double-stranded DNA (dsDNA) through the formation of a double-duplex invasion complex. This double-duplex invasion is hard to achieve with other artificial nucleic acids and is expected to be a promising method to recognize dsDNA in cellula or in vivo since the invasion does not require the prior denaturation of dsDNA. In this paper, we provide basic knowledge of PNA and mainly focus on the research of PNA invasion.

Switchable DNA-Encoded Chemical Library: Interconversion between Double- and Single-Stranded DNA Formats

DNA-Encoded Chemical Library (DEL) has attracted substantial attention due to the infinite possibility for hit discovery in both pharmaceutical companies and academia. The encoding method is the initial step of DEL construction and one of the cornerstones of DEL applications. Classified by the DNA format, the existing DEL encoding strategies could be categorized into single-stranded DNA-based strategies and double-stranded DNA-based strategies. The two DEL formats have their unique advantages but are usually incompatible with each other. To address this issue, we proposed the concept of interconversion between double- and single-stranded DEL based on the "reversible covalent headpiece (RCHP)" design, which combined maximum robustness of synthesis with extraordinary flexibility of applications in distinct setups. Future opportunities in this field were also proposed to advance DEL technology to a comprehensive drug discovery platform.

Rapid Alkene-Alkene Photo-Cross-Linking on the Base-Flipping-Out Field in Duplex DNA

Specific chemical reactions by enzymes acting on a nucleobase are realized by flipping the target base out of the helix. Similarly, artificial oligodeoxynucleotides (ODNs) can also induce the base flipping and a specific chemical reaction. We now report an easily prepared and unique structure-providing photo-cross-linking reaction by taking advantage of the base-flipping-out field formed by alkene-type base-flipping-inducing artificial bases. Two 3-arylethenyl-5-methyl-2-pyridone nucleosides with the Ph or An group were synthesized and incorporated into the ODNs. We found that the two Ph derivatives provided the cross-linked product in a high yield only by a 10 s photoirradiation when their alkenes overlap each other in the duplex DNA. The highly efficient reaction enabled forming a cross-linked product even when using the duplex with a low T_m value.

Photochemical modifications for DNA/RNA oligonucleotides

Light-triggered chemical reactions can provide excellent tools to investigate the fundamental mechanisms important in biology. Light is easily applicable and orthogonal to most cellular events, and its dose and locality can be controlled in tissues and cells. Light-induced conversion of photochemical groups installed on small molecules, proteins, and oligonucleotides can alter their functional states and thus the ensuing biological events. Recently, photochemical control of DNA/RNA structure and function has garnered attention thanks to the rapidly expanding photochemistry used in diverse biological applications. Photoconvertible groups can be incorporated in the backbone, ribose, and nucleobase of an oligonucleotide to undergo various irreversible and reversible light-induced reactions such as cleavage, crosslinking, isomerization, and intramolecular cyclization reactions. In this review, we gather a list of photoconvertible groups used in oligonucleotides and summarize their reaction characteristics, impacts on DNA/RNA thermal stability and structure, as well as their biological applications.

Synthesis and structure–activity relationship of peptide nucleic acid probes with improved interstrand-crosslinking abilities: application to biotin-mediated RNA-pulldown

After optimization of interstrand crosslink reaction between furan-containing peptide nucleic acids and target oligonucleotides, the reversibility of the formed product is exploited for the pull-down of a sequence of interest from cell lysates.

Mutations in artificial self-replicating tiles: A step toward Darwinian evolution

In nature, mutation is the first step of evolution, where it provides the genetic variation for the natural selection to act. Here we take a system of artificial self-replicating tiles, DNA origami, that exhibit templated reproduction. We can generate a small fraction of mutations by introducing a mismatch in hybridization between parent and daughter. We can modify the origami functionality to affect the growth rate of the mutated species, giving it less or more evolutionary advantage, and to become dominant in several generations. The introduction of mutations into an artificial self-replicating system provides new directions for research into self-assembly processes.

Artificial self-replication and exponential growth holds the promise of gaining a better understanding of fundamental processes in nature but also of evolving new materials and devices with useful properties. A system of DNA origami dimers has been shown to exhibit exponential growth and selection. Here we introduce mutation and growth advantages to study the possibility of Darwinian-like evolution. We seed and grow one dimer species, AB, from A and B monomers that doubles in each cycle. A similar species from C and D monomers can replicate at a controlled growth rate of two or four per cycle but is unseeded. Introducing a small mutation rate so that AB parents infrequently template CD offspring we show experimentally that the CD species can take over the system in approximately six generations in an advantageous environment. This demonstration opens the door to the use of evolution in materials design.

Mutation enrichment in human DNA samples via UV-mediated cross-linking

Detection of low-level DNA mutations can reveal recurrent, hotspot genetic changes of clinical relevance to cancer, prenatal diagnostics, organ transplantation or infectious diseases. However, the high excess of wild-type (WT) alleles, which are concurrently present, often hinders identification of salient genetic changes. Here, we introduce UV-mediated cross-linking minor allele enrichment (UVME), a novel approach that incorporates ultraviolet irradiation (∼365 nm UV) DNA cross-linking either before or during PCR amplification. Oligonucleotide probes matching the WT target sequence and incorporating a UV-sensitive 3-cyanovinylcarbazole nucleoside modification are employed for cross-linking WT DNA. Mismatches formed with mutated alleles reduce DNA binding and UV-mediated cross-linking and favor mutated DNA amplification. UV can be applied before PCR and/or at any stage during PCR to selectively block WT DNA amplification and enable identification of traces of mutated alleles. This enables a single-tube PCR reaction directly from genomic DNA combining optimal pre-amplification of mutated alleles, which then switches to UV-mediated mutation enrichment-based DNA target amplification. UVME cross-linking enables enrichment of mutated KRAS and p53 alleles, which can be screened directly via Sanger sequencing, high-resolution melting, TaqMan genotyping or digital PCR, resulting in the detection of mutation allelic frequencies of 0.001–0.1% depending on the endpoint detection method. UV-mediated mutation enrichment provides new potential for mutation enrichment in diverse clinical samples.

Reversible Covalent Headpiece Enables Interconversion between Double- and Single-Stranded DNA-Encoded Chemical Libraries

The use of a proper encoding methodology is one of the most important aspects when practicing DEL technology. A "headpiece"-based double-stranded DEL encoding method is currently the most widely used for productive DEL. However, the robustness of double-stranded DEL construction conflicts with the versatility presented by single-stranded DEL applications. We here report a novel encoding method, which is based on a "reversible covalent headpiece (RCHP)". The RCHP allows reversible interconversion between double- and single-stranded DNA formats, providing an avenue to robust synthesis and allowing for the applications in distinct setups. We have validated the versatility of this encoding method with encoded self-assembled chemical library and DNA-encoded dynamic library technology. Notably, based on the RCHP-settled library construction, a unique "ternary covalent complex" mediating ligand isolation methodology against non-immobilized targets was developed.

The Inhibition Effect of Photo-Cross-Linking between Probes in Photo-Induced Double Duplex Invasion DNA

Double duplex invasion (DDI) DNA is a useful antigene method that inhibits expression of genomic DNA. We succeeded in performing photoinduced-DDI (pDDI) using ultrafast photo-cross-linking. 5-Cyanouracil (^CN U) has been used in pDDI to inhibit photo-cross-linking between probes, but its importance has not been clarified. Therefore, in this study, we evaluated the effect of spacer (S) and d-spacer (dS) that exhibit photo-cross-linking ability similar to that of ^CN U. ^CN U exhibited the highest pDDI efficiency, and S, dS, and T were not very different. The photo-cross-linking inhibitory effect was better with S and dS than with thymidine (T). Conversely, the thermal stability was significantly lower with S and dS than with T. The results suggest that the pDDI efficiency is determined by the balance between the photo-cross-linking inhibitory effect and the thermal stability, which is the introduction efficiency for double-stranded DNA. Therefore, ^CN U, which has a photo-cross-linking inhibitory effect and a high T_m value, showed the highest inhibitory efficiency.

Chemically modified nucleic acids and DNA intercalators as tools for nanoparticle assembly

The self-assembly of inorganic nanoparticles to larger structures is of great research interest as it allows the fabrication of novel materials with collective properties correlated to the nanoparticles' individual characteristics. Recently developed methods for controlling nanoparticle organisation have enabled the fabrication of a range of new materials. Amongst these, the assembly of nanoparticles using DNA has attracted significant attention due to the highly selective recognition between complementary DNA strands, DNA nanostructure versatility, and ease of DNA chemical modification. In this review we discuss the application of various chemical DNA modifications and molecular intercalators as tools for the manipulation of DNA-nanoparticle structures. In detail, we discuss how DNA modifications and small molecule intercalators have been employed in the chemical and photochemical DNA ligation in nanostructures; DNA rotaxanes and catenanes associated with reconfigurable nanoparticle assemblies; and DNA backbone modifications including locked nucleic acids, peptide nucleic acids and borane nucleic acids, which affect the stability of nanostructures in complex environments. We conclude by highlighting the importance of maximising the synergy between the communities of DNA chemistry and nanoparticle self-assembly with the aim to enrich the library of tools available for the manipulation of nanostructures.

Visible-Light-Mediated Modification and Manipulation of Biomacromolecules

Chemically modified biomacromolecules-i.e., proteins, nucleic acids, glycans, and lipids-have become crucial tools in chemical biology. They are extensively used not only to elucidate cellular processes but also in industrial applications, particularly in the context of biopharmaceuticals. In order to enable maximum scope for optimization, it is pivotal to have a diverse array of biomacromolecule modification methods at one's disposal. Chemistry has driven many significant advances in this area, and especially recently, numerous novel visible-light-induced photochemical approaches have emerged. In these reactions, light serves as an external source of energy, enabling access to highly reactive intermediates under exceedingly mild conditions and with exquisite spatiotemporal control. While UV-induced transformations on biomacromolecules date back decades, visible light has the unmistakable advantage of being considerably more biocompatible, and a spectrum of visible-light-driven methods is now available, chiefly for proteins and nucleic acids. This review will discuss modifications of native functional groups (FGs), including functionalization, labeling, and cross-linking techniques as well as the utility of oxidative degradation mediated by photochemically generated reactive oxygen species. Furthermore, transformations at non-native, bioorthogonal FGs on biomacromolecules will be addressed, including photoclick chemistry and DNA-encoded library synthesis as well as methods that allow manipulation of the activity of a biomacromolecule.

Photocrosslinking of DNA using 4-methylpyranocarbazole nucleoside with thymine base selectivity

This report describes a novel photocrosslinker, 4-methylpyranocarbazole nucleoside (^MEPK), that can be induced to crosslink using visible light. Previously, we reported a visible light-responsive artificial nucleic acid, pyranocarbazole nucleoside (^PCX). ^MEPK can selectively photocrosslink to thymine bases in a complementary nucleic acid strand. It was synthesized by introducing a methyl group at the 4-position of ^PCX, and it can differentiate between thymine and cytosine. The previously reported visible light-responsive artificial nucleic acid ^PCX has a low synthetic yield. ^MEPK was synthesized by Pechmann condensation which suppressed by-product formation, making the synthesis more efficient, and resulting in a higher yield than that of ^PCX. ^MEPK is expected to have practical applications as a photocrosslinker that can be manipulated with visible light and that selectively targets thymine bases.

Completing the canvas: advances and challenges for DNA-PAINT super-resolution imaging

Single-molecule localization microscopy (SMLM) is a potent tool to examine biological systems with unprecedented resolution, enabling the investigation of increasingly smaller structures. At the forefront of these developments is DNA-based point accumulation for imaging in nanoscale topography (DNA-PAINT), which exploits the stochastic and transient binding of fluorescently labeled DNA probes. In its early stages the implementation of DNA-PAINT was burdened by low-throughput, excessive acquisition time, and difficult integration with live-cell imaging. However, recent advances are addressing these challenges and expanding the range of applications of DNA-PAINT. We review the current state of the art of DNA-PAINT in light of these advances and contemplate what further developments remain indispensable to realize live-cell imaging.

DNA Assembly-Based Stimuli-Responsive Systems

Stimuli-responsive designs with exogenous stimuli enable remote and reversible control of DNA nanostructures, which break many limitations of static nanostructures and inspired development of dynamic DNA nanotechnology. Moreover, the introduction of various types of organic molecules, polymers, chemical bonds, and chemical reactions with stimuli-responsive properties development has greatly expand the application scope of dynamic DNA nanotechnology. Here, DNA assembly-based stimuli-responsive systems are reviewed, with the focus on response units and mechanisms that depend on different exogenous stimuli (DNA strand, pH, light, temperature, electricity, metal ions, etc.), and their applications in fields of nanofabrication (DNA architectures, hybrid architectures, nanomachines, and constitutional dynamic networks) and biomedical research (biosensing, bioimaging, therapeutics, and theranostics) are discussed. Finally, the opportunities and challenges for DNA assembly-based stimuli-responsive systems are overviewed and discussed.

Photo-reactive oligodeoxynucleotide-embedded nanovesicles (PROsomes) with switchable stability for efficient cellular uptake and gene knockdown

A photo-responsive nanovesicle is fabricated by polyion complex (PIC) formation between poly(ethylene glycol) (PEG)-block-polypeptides and photo-reactive oligodeoxynucleotides (PROs)/anti-sense oligonucleotides (ASOs). The ultraviolet (UV) light triggers reversible crosslinking between PROs and ASOs in the vesicular membrane, providing the nanovesicle with switchable stability under physiological conditions. The resulting nanovesicle allows efficient cellular internalization, leading to significant UV-triggered gene knockdown in cultured cells.

Crosslinker-modified nucleic acid probes for improved target identification and biomarker detection

Understanding the intricate interaction pattern of nucleic acids with other molecules is essential to gain further insight in biological processes and disease mechanisms. To this end, a multitude of hybridization-based assays have been designed that rely on the non-covalent recognition between complementary nucleic acid sequences. However, the ephemeral nature of these interactions complicates straightforward analysis as low efficiency and specificity are rule rather than exception. By covalently locking nucleic acid interactions by means of a crosslinking agent, the overall efficiency, specificity and selectivity of hybridization-based assays could be increased. In this mini-review we highlight methodologies that exploit the use of crosslinker-modified nucleic acid probes for interstrand nucleic acid crosslinking with the objective to study, detect and identify important targets as well as nucleic acid sequences that can be considered relevant biomarkers. We emphasize on the usefulness and advantages of crosslinking agents and elaborate on the chemistry behind the crosslinking reactions they induce.

Mechanical Properties of DNA Hydrogels: Towards Highly Programmable Biomaterials

DNA hydrogels are self-assembled biomaterials that rely on Watson–Crick base pairing to form large-scale programmable three-dimensional networks of nanostructured DNA components. The unique mechanical and biochemical properties of DNA, along with its biocompatibility, make it a suitable material for the assembly of hydrogels with controllable mechanical properties and composition that could be used in several biomedical applications, including the design of novel multifunctional biomaterials. Numerous studies that have recently emerged, demonstrate the assembly of functional DNA hydrogels that are responsive to stimuli such as pH, light, temperature, biomolecules, and programmable strand-displacement reaction cascades. Recent studies have investigated the role of different factors such as linker flexibility, functionality, and chemical crosslinking on the macroscale mechanical properties of DNA hydrogels. In this review, we present the existing data and methods regarding the mechanical design of pure DNA hydrogels and hybrid DNA hydrogels, and their use as hydrogels for cell culture. The aim of this review is to facilitate further study and development of DNA hydrogels towards utilizing their full potential as multifeatured and highly programmable biomaterials with controlled mechanical properties.

Engineering Aptamer Switches for Multifunctional Stimulus-Responsive Nanosystems

Although RNA and DNA are best known for their capacity to encode biological information, it has become increasingly clear over the past few decades that these biomolecules are also capable of performing other complex functions, such as molecular recognition (e.g., aptamers) and catalysis (e.g., ribozymes). Building on these foundations, researchers have begun to exploit the predictable base-pairing properties of RNA and DNA in order to utilize nucleic acids as functional materials that can undergo a molecular "switching" process, performing complex functions such as signaling or controlled payload release in response to external stimuli including light, pH, ligand-binding and other microenvironmental cues. Although this field is still in its infancy, these efforts offer exciting potential for the development of biologically based "smart materials". Herein, ongoing progress in the use of nucleic acids as an externally controllable switching material is reviewed. The diverse range of mechanisms that can trigger a stimulus response, and strategies for engineering those functionalities into nucleic acid materials are explored. Finally, recent progress is discussed in incorporating aptamer switches into more complex synthetic nucleic acid-based nanostructures and functionalized smart materials.

Complete Photochemical Regulation of 8-17 DNAzyme Activity by Using Reversible DNA Photo-crosslinking

The regulation of DNAzyme activity is an important problem for its in vivo applications. We achieved photochemical regulation of DNAzyme activity by using reversible DNA photo-crosslinking of 3-cyanovinylcarbazole (^CNV K). The ODN containing ^CNV K photo-crosslinked to a pyrimidine base in the complementary strand after a few seconds of photoirradiation, and its photoadduct was split by photoirradiation of another wavelength. The activity of photo-crosslinked DNAzyme with ^CNV K was completely inhibited (OFF state). In contrast, after 312 nm irradiation, DNAzyme activity was recovered upon addition of a substrate strand (ON state). In addition, the photo-crosslinked DNAzyme is prone to enzymatic digestion by exonuclease. This photochemical OFF to ON switching with reversible DNA photo-crosslinking was regulated at the desired time and position; therefore, it might be possible to use it for in vivo application.

Photochemical RNA Editing of C to U by Using Ultrafast Reversible RNA Photo-crosslinking in DNA/RNA Duplexes

RNA editing, which is used to edit nucleobases in RNA strands; is more feasible for use in medical applications than DNA editing. We previously reported the photochemical conversion of cytosine to uracil, which required photo-crosslinking, deamination, and photo-splitting. Here, we evaluated the influence of the bases surrounding the target cytosine on the conversion of cytosine to uracil in the RNA strand. The photo-crosslinker 3-carboxyvinylcarbazole(^OHV K), which is more hydrophilic than 3-cyanovinylcarbazole(^CNV K), 3-carboxyamidevinylcarbazole(^NH2V K), and 3-methoxy carbonylvinylcarbazole(^OMeV K), induced faster deamination of cytosine. Furthermore, inosine, which forms two hydrogen bonds with cytosine, was the most efficiently paired base for accelerating photochemical RNA editing. Upon evaluation of the conversion from cytosine to uracil in RNA, the use of oligodeoxynucleotides containing ^OHV K and inosine and the polarity of the bases surrounding the target cytosine were found to be crucial.

Visible-light triggered templated ligation on surface using furan-modified PNAs

Oligonucleotide-templated reactions are frequently exploited for target detection in biosensors and for the construction of DNA-based materials and probes in nanotechnology. However, the translation of the specifically used template chemistry from solution to surfaces, with the final aim of achieving highly selective high-throughput systems, has been difficult to reach and therefore, poorly explored. Here, we show the first example of a visible light-triggered templated ligation on a surface, employing furan-modified peptide nucleic acids (PNAs). Tailored photo-oxidation of the pro-reactive furan moiety is ensured by the simultaneous introduction of a weak photosensitizer as well as a nucleophilic moiety in the reacting PNA strand. This allows one to ensure a localized production of singlet oxygen for furan activation, which is not affected by probe dilution or reducing conditions. Simple white light irradiation in combination with target-induced proximity between reactive functionalities upon recognition of a short 22mer DNA or RNA sequence that functions as a template, allows sensitive detection of nucleic acid targets in a 96 well plate format.

Molecular swarm robots: recent progress and future challenges

Recent advancements in molecular robotics have been greatly contributed by the progress in various fields of science and technology, particularly in supramolecular chemistry, bio- and nanotechnology, and informatics. Yet one of the biggest challenges in molecular robotics has been controlling a large number of robots at a time and employing the robots for any specific task as flocks in order to harness emergent functions. Swarming of molecular robots has emerged as a new paradigm with potentials to overcome this hurdle in molecular robotics. In this review article, we comprehensively discuss the latest developments in swarm molecular robotics, particularly emphasizing the effective utilization of bio- and nanotechnology in swarming of molecular robots. Importance of tuning the mutual interaction among the molecular robots in regulation of their swarming is introduced. Successful utilization of DNA, photoresponsive molecules, and natural molecular machines in swarming of molecular robots to provide them with processing, sensing, and actuating ability is highlighted. The potentials of molecular swarm robots for practical applications by means of their ability to participate in logical operations and molecular computations are also discussed. Prospects of the molecular swarm robots in utilizing the emergent functions through swarming are also emphasized together with their future perspectives.

Effect of linker length on photo-cross-linking position mediated by click chemistry via [2 + 2] photocycloaddition†

Ultrafast reversible DNA/RNA photo-cross-linking is a powerful tool for regulating the target strand in living cells. In particular, 3-cyanovinylcarbazole (CNVK) and 3-cyanovinylcarbazole modified by D-threoninol (CNVD) can photo-cross-link to pyrimidine bases within a few seconds of photoirradiation. However, these photo-cross-linkers can only cross-link to the counter base if it is adjacent to the 5'-side (-1 position). In this study, we synthesized novel photo-cross-linkers with varying linker lengths capable of photo-cross-linking with pyrimidine bases at locations other than the -1 position via click chemistry. The photo-cross-linking site was dependent on linker length.

Photo-printing of faceted DNA patchy particles

Patchy particles with shape complementarity can serve as building blocks for assembling colloidal superstructures. Alternatively, encoding information on patches using DNA can direct assembly into a variety of crystalline or other preprogrammed structures. Here, we present a tool where DNA is used both to engineer shape and to encode information on colloidal particles. Two reactive oil emulsions with different but complementary DNA (cDNA) brushes are assembled into CsCl-like crystalline lattices. The DNA brushes are recruited to and ultimately localized at the junctions between neighboring droplets, which gives rise to DNA-encoded faceted patches. The emulsions are then solidified by ultraviolet (UV) polymerization, producing faceted patchy particles. The facet size and DNA distribution are determined by the balance between the DNA binding energy and the elastic deformation energy of droplets. This method leads to a variety of new patchy particles with directional interactions in scalable quantities.

Photocrosslinking of cDNA Display Molecules with Their Target Proteins as a New Strategy for Peptide Selection

Binding peptides for given target molecules are often selected in vitro during drug discovery and chemical biology research. Among several display technologies for this purpose, complementary DNA (cDNA) display (a covalent complex of a peptide and its encoding cDNA linked via a specially designed puromycin-conjugated DNA) is unique in terms of library size, chemical stability, and flexibility of modification. However, selection of cDNA display libraries often suffers from false positives derived from non-specific binding. Although rigorous washing is a straightforward solution, this also leads to the loss of specific binders with moderate affinity because the interaction is non-covalent. To address this issue, herein, we propose a method to covalently link cDNA display molecules with their target proteins using light irradiation. We designed a new puromycin DNA linker that contains a photocrosslinking nucleic acid and prepared cDNA display molecules using the linker. Target proteins were also labeled with a short single-stranded DNA that should transiently hybridize with the linker. Upon ultraviolet (UV) light irradiation, cDNA display molecules encoding correct peptide aptamers made stable crosslinked products with the target proteins in solution, while display molecules encoding control peptides did not. Although further optimization and improvement is necessary, the results pave the way for efficient selection of peptide aptamers in multimolecular crowding biosystems.

Super-resolution labelling with Action-PAINT

Recent advances in localisation-based super-resolution microscopy have enabled researchers to visualise single molecular features down to individual molecular components (~5 nm), but do not yet allow manipulation of single-molecule targets in a user-prescribed, context-dependent manner. Here we report an “Action-PAINT” strategy for super-resolution labelling upon visualisation on single molecules. This approach monitors and localises DNA binding events in real-time with DNA-PAINT, and upon visualisation of binding to a desired location, photo-crosslinks the DNA to affix the molecular label. We showed the efficiency of 3-cyanovinylcarbazole nucleoside (CNVK) photo-inducible crosslinking on single molecular targets and developed a software package for real-time super-resolution imaging and crosslinking control. We then benchmarked our super-resolution labelling method on synthetic DNA nanostructures and demonstrated targeted multi-point labelling on various complex patterns with 30 nm selectivity. Finally, we performed targeted in situ labelling on fixed microtubule samples with 40 nm target size and custom-controlled, sub-diffraction spacing.

Super-Resolution Optical Lithography with DNA

We developed an efficient, versatile, and accessible super-resolution microscopy method to construct a nanoparticle assembly at a spatial resolution below the optical diffraction limit. The method utilizes DNA and a photoactivated DNA cross-linker. Super-resolution optical techniques have been used only as a means to make measurements below the light diffraction limit. Furthermore, no optical technique is currently available to construct nanoparticle assemblies with a precisely designed shape and internal structure at a resolution of a few tens of nanometers (nm). Here we demonstrate that we can fulfill this deficiency by utilizing spontaneous structural dynamics of DNA hairpins combined with single-molecule fluorescence resonance energy transfer (smFRET) microscopy and a photoactivated DNA cross-linker. The stochastic fluorescence blinking due to the spontaneous folding and unfolding motions of DNA hairpins enables us to precisely localize a folded hairpin and solidify it only when it is within a predesigned target area whose size is below the diffraction limit. As the method is based on an optical microscope and an easily clickable DNA cross-linking reagent, it will provide an efficient means to create large nanoparticle assemblies with a shape and internal structure at an optical super-resolution, opening a wide window of opportunities toward investigating their photophysical and optoelectronic properties and developing novel devices.

Multi-level patterning nucleic acid photolithography

The versatile and tunable self-assembly properties of nucleic acids and engineered nucleic acid constructs make them invaluable in constructing microscale and nanoscale devices, structures and circuits. Increasing the complexity, functionality and ease of assembly of such constructs, as well as interfacing them to the macroscopic world requires a multifaceted and programmable fabrication approach that combines efficient and spatially resolved nucleic acid synthesis with multiple post-synthetic chemical and enzymatic modifications. Here we demonstrate a multi-level photolithographic patterning approach that starts with large-scale in situ surface synthesis of natural, modified or chimeric nucleic acid molecular structures and is followed by chemical and enzymatic nucleic acid modifications and processing. The resulting high-complexity, micrometer-resolution nucleic acid surface patterns include linear and branched structures, multi-color fluorophore labeling and programmable targeted oligonucleotide immobilization and cleavage.

Reversible photo-cross-linking of the GCN4 peptide containing 3-cyanovinylcarbazole amino acid to double-stranded DNA

Interaction analysis in vivo greatly promotes the analyses and understanding of biological functions. The interaction between DNA and peptides or proteins is very important in terms of readout and amplifying information from genomic DNA. In this study, we designed and synthesized a photo-cross-linkable amino acid, l-3-cyanovinlycarbazole amino acid (l-CNVA), to double-stranded DNA. Reversible photo-cross-linking between DNA and peptides containing CNVA, having 3-cyanovinylcarbazole moieties capable of photo-cross-linking to nucleic acids, was demonstrated. As a result, it was shown that the GCN4 peptide, containing CNVA, can be photo-cross-linked to DNA, and its adduct was photo-split into the original peptide and DNA with 312 nm-irradiation. This is the first report that reversibly manipulates photo-crosslinking between double stranded DNA and peptides. In addition, this reversible photo-cross-linking, using l-CNVA, is faster and with higher yield than that using diazirine and psoralen.