1 Introduction
Deoxyribonucleic acid (DNA), as an important biological macromolecule responsible for storing and transmitting genetic information, has attracted great attention in recent years as a structural element to construct DNA nanostructures and nanodevices. Since Professor Seeman proposed "structural DNA nanotechnology" in 1982, scientists have taken advantage of the precise molecular recognition characteristics, sequence programmability and nanoscale size of DNA.One-dimensional, two-dimensional and three-dimensional DNA nanostructures and dynamic nanodevices have been successfully constructed, and the preparation and application of a variety of responsive DNA hydrogels have been realized through rational design. DNA composite nanostructures and DNA nanotechnology can also be applied in the fields of biomedicine, bionics and nanoscience
[1][2⇓⇓⇓⇓⇓~8][9⇓⇓~12][13,14][15,16][17][18].
With the development of DNA synthesis technology and chemical modification methods, organic molecules with diverse structures and rich functions can be modified to any site of the DNA strand. At present, the reported molecules covalently linked to DNA are divided into synthetic polymers, dendrimers, biomacromolecules such as peptides or proteins, and small molecules such as fluorescent molecules and lipid molecules. These DNA hybrids, as a new class of building blocks, lay the foundation for the construction of biofunctional nanostructures. DNA-organic molecular hybrids not only have the characteristics of precise recognition, sequence programmability and nanoscale size of DNA, but also combine the characteristics of structural designability, diversity and responsiveness of organic molecules, which bring excellent properties to the assembly of amphiphilic DNA hybrids. At the same time, these DNA-organic molecular hybrids can be assembled into spherical micelles, nanofibers, vesicles, nanoribbons and other assemblies through the design of DNA sequence length and conformation, and the selection of organic molecular species. The high-density DNA sequence around the assembly can effectively increase the targeting effect and functional load of the assembly, and the hydrophobic region of the inner core can be loaded with drug molecules or functional molecules. These assemblies can also be used as templates for the study of organic chemical reactions, or as templates for the alignment of inorganic nanoparticles. Therefore, DNA-organic molecular assemblies have important applications in the fields of drug delivery, targeted delivery and biosensing. At present, the assembly and application of DNA-polymer block copolymers and DNA-peptide/protein have been reviewed, and these DNA structural motifs have been widely used in the preparation of nanomaterials, drug delivery, gene delivery and other biomedical fields
[19⇓~21][22,23].
Small hydrophobic molecules, due to their small molecular size, are not amphiphilic enough to support further assembly after covalent modification of DNA, so the development of small molecular covalent DNA assembly is relatively slow. In recent years, researchers have increased the hydrophobic ratio by increasing the topological structure of hydrophobic molecules through functional group derivation or by expanding aromatic rings to enhance π-π stacking, so as to realize the assembly of DNA-organic small molecules into nanostructures with diverse morphologies and excellent functions in aqueous phase. Therefore, in this paper, we mainly review the recent progress in the assembly of small organic molecule covalent DNA, as well as the potential applications of DNA nanomaterials in the biomedical field, and look forward to the future of these DNA nanomaterials.
2 Assembly of DNA-small organic molecule hybrids.
There are two main methods for chemical modification of DNA sequences: solid-phase synthesis and solution-phase coupling, which have been reviewed in detail
[24]. In recent years, a series of new strategies have been reported, such as alkynyl-copper azide catalyzed cycloaddition, polymerase chain reaction (PCR), polymer initiator modification of DNA ends, surfactant assisted reaction, and DNA micelle template. These synthetic techniques lay the foundation for the further assembly of DNA-organic molecular hybrids
[25][26][27][28][29].
Synthetic DNA-organic small molecules not only have the characteristics of precise recognition, sequence programmability, nanoscale size and good biocompatibility of DNA, but also have the characteristics of temperature sensitivity, photosensitivity, acid-base response, fluorescence or host-guest recognition of small molecules. These characteristics will bring new applications for the application of its assembly structure.
Considering the self-assembly of DNA-small organic molecules driven by hydrophilic-hydrophobic interaction, the construction of DNA-small organic molecules can be divided into two strategies: (1) hydrophobic small molecules are directly covalently linked to DNA, and DNA-organic small molecule hybrids are self-assembled under hydrophilic-hydrophobic interaction. These hydrophobic small molecules include lipid molecules, fluorescent molecules and other π-system molecules. (2) Superamphiphilic DNA-organic molecules are constructed by host-guest chemistry, and further assembled and regulated, in which the host molecules include cyclodextrin, cucurbit [n] uril, etc.
2.1 Self-assembly of DNA-small organic molecule hybrids.
2.1.1 Assembly of DNA-lipid amphiphiles.
The structure of lipid molecules is similar to the hydrophobic part of the cell membrane, so DNA-lipid amphiphiles are more likely to interact with the cell membrane than other hydrophobic molecules and can be efficiently absorbed by cells. Gosse and Jullien et al. First reported the synthesis of DNA-lipid amphiphiles modified with fluorescent molecules, in which the lipid molecule consists of two hexadecyl carbon chains
[30]. The experimental results show that the melting point of DNA double strand hybridization is increased by lipid molecules, indicating that the stability is increased. Subsequently, Dentinger et al. Reported the synthesis and assembly of tetradecyl chain-modified DNA
[31]. Experiments show that the amphiphilic DNA molecule can be assembled into vesicles in water phase and has a hydrophobic fluorescent molecule orange OT, which proves that the tetradecyl chain is in the interior of the vesicle to form a hydrophobic cavity; By introducing a complementary DNA sequence, increasing the hydrophilic ratio causes the vesicles to dissociate and release hydrophobic molecules. This indicates that it has potential applications in drug delivery and delivery.
Through the precise recognition of DNA bases, the assembly regulation of DNA-organic small molecules can be realized, and the application of DNA nano-assemblies can be expanded. In 2010, Gianneschi's group used the precise recognition of DNA bases to achieve reversible regulation of assembly morphology
[32]. As shown in Figure 1A, DNA 1 (9-base covalent two octadecyl chains) assembled into 500 nm vesicles, and the transition of vesicles to small spherical micelles was achieved by introducing polyethylene glycol (PEG) modified partial complementary DNA sequence (DNA 2) to change the hydrophilic and hydrophobic ratio. Similarly, reversible conversion can be achieved by adding the fully complementary pairing sequence D3 to D2.
On the other hand, using the conformational diversity of DNA, the packing tightness of DNA in different conformations is different, which may cause the change of assembly morphology, thus achieving morphology regulation. Sun Yawei's team reported the assembly behavior of DNA-C18 with pH response, in which the hydrophobic molecule is an octadecyl chain and the DNA is a cytosine-rich sequence
[33]. At pH 4.5, the DNA sequence can form a compact bimolecular i-motif structure, and at pH 9, it is a flexible single-stranded structure. Based on its conformational change, a 50 nm multilayer aggregate is formed at pH 4.5; At pH 9, spherical micelles were first assembled, and then large micellar aggregates with a diameter of more than 100 nm were formed. These pH-responsive nanostructures with different sizes are expected to be used as nanomaterials for controlled drug delivery systems. In 2017, Tan Weihong's team reported the stabilization and dissociation of DNA-lipid spherical micelles in the presence of serum albumin by regulating the conformation of guanine G-rich sequences
[34]. As shown in fig. 1b, in the DNA-lipid molecule, a guanine sequence is inserted into the DNA sequence. When intermolecular DNA quadruplex (G-quadruplex) is formed, it can assemble into stable "locked" spherical micelles, which are not easily decomposed by serum albumin. When irradiated by ultraviolet light, DNA quadruplexes dissociate to form G-C paired double-stranded DNA, and the spherical micelles under this condition are easily dissociated by serum albumin, thus achieving effective uptake by cells. These results indicate that the stable encapsulation of drug molecules in the assembly and the efficient uptake of cells can be achieved through the change of DNA conformation.
2.1.2 Assembly of Amphiphilic DNA-Fluorescent Molecular Hybrid
In addition to the covalent attachment of lipid molecules to DNA, fluorescent molecules not only have their own unique fluorescent properties, but also can be used as hydrophobic molecules to covalently attach to DNA to prepare amphiphilic DNA-fluorescent molecule hybrids. In recent years, the assembly of hybrids after covalent DNA of fluorescent molecules has also attracted the attention of scientists. Here we focus on the assembly behavior of amphiphilic DNA-fluorescent molecule hybrids, including perylene imide and pyrene.
Perylene diimides (PDIs) are a prominent class of fluorescent dyes due to their strong photostability, chemical stability, and high fluorescence quantum yield. In 2004, M Müllen and R Rädler successfully modified the DNA sequence at both ends of PDI (ssODN-PDI-ssODN) by using the solid-phase synthesis technology of DNA, which broke through the difficulty of covalent connection between PDI and DNA strand, and proved that ssODN-PDI-ssODN could be dissolved in organic solvents by adding cationic liposomes
[35]. In 2009, Lewis and Rybtchinski reported a dumbbell-like structure of double-stranded DNA with PDI at both ends, and constructed a one-dimensional supramolecular polymer based on the strong hydrophobic interaction and π-π stacking between PDI molecules
[36]. In 2017, the team further systematically studied the assembly behavior of ssDNA-PDI in the aqueous phase
[37]. They investigated the effect of a range of different sequence lengths and specific base components on the assembly topography. The results showed that PDI-ssDNA formed nanofibers when the sequence contained 1 ~ 3 bases. When the sequence is TA4-5 or GC4-5, it assembles into a bilayer membrane structure and a large network structure through the base-pairing interaction between strands and the π-π stacking of PDI, respectively.
In 2019, Liu Simin's group reported the assembly behavior of DNA-PDI hybrids based on the host-guest recognition of cucurbit [10] uril (CB [10]) and PDI (Figure 2A)
[38]. Wherein the DNA sequence is a single strand containing 18 bases. D18-PDI assembled into spherical micelles with a diameter of 20 nm in the aqueous phase. Based on the host-guest recognition between CB [10] and PDI, with the addition of the host molecule CB [10], the assembly morphology changed from spherical micelles to two-dimensional DNA nanosheets under the action of host-guest interaction and π-π stacking. The system can realize the reversible regulation between the two-dimensional nanosheet and the spherical micelle through the host-guest action and the addition of a competitive guest, and the like; and meanwhile, the two-dimensional nanosheet has addressability, and can realize the directional arrangement of the gold nanoparticles through DNA base pairing. This lays a foundation for the research of DNA nanostructures in drug delivery, controlled release and other fields.
Compared with perylene imide, the molecular size of pyrene is smaller, and the amphiphilic DNA hybrid prepared by covalent attachment of pyrene and DNA has a small hydrophobic ratio, so can it assemble into a regular morphology in aqueous phase? H Häner's group has done a series of studies on the properties and assembly of DNA-pyrene covalent hybrids. H Häner's group reported the effects of pyrene covalent insertion into DNA sequences on DNA double-strand hybridization and ultraviolet spectral properties, and found that DNA-pyrene hybrids have higher quantum yields and can be used as diagnostic tools based on molecular beacons
[39]. Subsequently, H Häner's team successfully synthesized oligomeric pyrene chimeric DNA hybrids, which are connected by phosphodiester bonds between pyrene molecules and between pyrene molecules and DNA sequences
[40]. DNA-grafted supramolecular polymers were constructed through hydrophobic interaction and π-π stacking interaction between pyrene molecules, and were observed to assemble into helical ribbon structures up to hundreds of nanometers (Fig. 2b), and the assembly morphology could be reversibly regulated by changing the temperature. This method provides a new idea for the application of supramolecular polymers in materials science and diagnostics. On this basis, the transformation from ribbon structure to network structure was realized by introducing complementary strands, and the loading of gold nanoparticles was realized by introducing gold nanoparticles modified by complementary sequences, which proved that the system could be used as a nanocarrier and an assembly framework, and expanded the application of assemblies
[41][42].
2.1.3 Assembly of DNA with other small molecule hybrids.
Small molecules covalently linked to DNA include, in addition to lipids and fluorescent molecules, other small organic molecules with excellent properties. For example, small organic molecules that can undergo fluorescence resonance energy transfer (FRET) with fluorescent molecules, azobenzene molecules that are responsive to light stimulation, and other molecules with more rigid and hydrophobic systems. The amphiphilic hybrids composed of these small molecules and DNA can also form assemblies with various morphologies under the driving forces of hydrophilicity and hydrophobicity.
Varghese's team used a solid-phase "click chemistry" approach to prepare a series of DNA-OPE (oligo (p-phenyleneethynylene)) amphiphilic hybrids that assemble into nano- or microsized vesicles with enhanced fluorescence intensity in solution (Figure 3A)
[43]. By using the addressability of DNA, the periphery of the vesicle can be loaded with gold nanoparticles, and can also be recognized by the complementary strand modified by acetylperylene, and the morphology is transformed into a columnar fiber. At the same time, it is proved that there is a FRET effect between the hydrophobic part of the DNA-OPE vesicle and acetylperylene, which provides a new strategy for the construction of artificial light harvesting systems. Subsequently, based on the conformational change of DNA, the research group constructed pH-responsive DNA nanovesicles and three-dimensional DNA network structure system, which laid the foundation for the controlled release of drugs
[44].
Morphological transformation may also be caused by the change of hydrophilic-hydrophobic ratio by the change of molecular configuration. In 2015, Zauscher and Brittain reported the synthesis of amphiphilic DNA-azobenzene hybrids and their light-stimulated regulation
[45]. Under the illumination of 430 nm, DNA-azobenzene hybrids assembled into spherical micelles. Micelle dissociation after 365 nm light stimulation. This is due to the fact that 365 nm light irradiation changes the structure of azobenzene from trans to cis, and the molecular size of cis-azobenzene is shorter than that of trans-azobenzene, which changes the hydrophilic-hydrophobic ratio, and at this ratio, the driving force of amphiphiles is not enough to support the formation of assemblies.
Compared with other π systems, the molecular structure of azobenzene is simple, so what kind of breakthrough will be made when the large π system with rigid structure binds to DNA? Varghese's team covalently linked DNA with six deca-alkyl chains modified by hexabenzocene (HBC), which can be assembled into ordered two-dimensional DNA nanosheets driven by amphiphilic interaction and π-π stacking, with a height of only nanometer and a length and width of several microns
[46]. The sheet-like structure not only has crystal characteristics, but also has the addressability of DNA, which can be loaded with high-density gold nanoparticles and is expected to be used in catalysis, sensing, biomolecular recognition and other fields. Subsequently, the group prepared amphiphilic hybrids in which the hydrophobic molecule hexaphenylbenzene was covalently linked to DNA (Figure 3B)
[47]. Hexaphenylbenzene has a propeller-like spatial structure. During the assembly process, the chirality of ssDNA is transferred to hexaphenylbenzene, so that the final assembled structure is a left-handed helical DNA nanoribbon. This opens up a direction for its application in chiral sensing, enantioselective synthesis, and photonic materials.
Phenanthrene molecules are similar to azobenzene molecules, and the hydrophobic system is small. In order to make up for this shortcoming, H Häner's group used the unit repetition strategy to expand the hydrophobic part and enhance the hydrophobicity. H Häner's team connected three phenanthrene molecules at the 3 'end of DNA and complementary strand respectively, and assembled the primary structure of dsDNA in the middle of phenanthrene at both ends through DNA complementary pairing
[48]. When spermine solution is added, the phenanthrene structures at both ends can act as sticky ends to connect the DNA double strands and assemble into vesicles with a diameter of 50-200 nm. It is found that the phenanthrene in the assembly has light harvesting properties and can transfer the absorbed energy to the acceptor, so the assembly is expected to expand its application by using the precise recognition characteristics of DNA.
2.2 Self-assembly of supra-amphiphilic DNA structures based on host-guest interactions.
In recent years, supraamphiphilic compounds constructed by non-covalent bonding (host-guest interaction, hydrogen bonding, etc.) And their assembly have also become the research focus of researchers
[49,50]. Cyclodextrin (CD) and cucurbituril (CB [n]), as host molecules, have non-toxic and harmless properties, and different cavity sizes can accommodate specific guest molecules of different sizes to form stable inclusion complexes. Therefore, the introduction of host-guest interaction to construct DNA superamphiphilic compounds provides a new idea for the preparation of DNA nanostructures.
Cyclodextrin (CD) has been popular as a host molecule with excellent water solubility, especially β-cyclodextrin (β-CD), which has a suitable cavity size and can form stable inclusion complexes with ferrocene, adamantane and other guest molecules. Chiba and Inouye's team used ssDNA modified by β-CD and complementary DNA strands modified by adamantane derivatives to construct supramolecular polymers of double-stranded DNA through the host-guest interaction between β-CD and adamantane derivatives and the complementary base pairing property of DNA
[51]. Moreover, the melting point (T
m value) of the double-stranded DNA structure based on the host-guest interaction is higher than that of the direct double-stranded DNA with the same sequence length, indicating that the host-guest interaction helps to enhance the stability of double-stranded DNA. In 2017, Varghese's group used ssDNA modified by β-CD as a hydrophilic host and adamantane derivatives modified by two and three dodecyl chains as hydrophobic guests to construct supra-amphiphilic DNA compounds by host-guest recognition and assemble them into vesicles (Figure 4A)
[52]. Because there are a large number of DNA strands on the surface of vesicles, gold nanoparticles modified by complementary strands can be loaded by base complementary pairing. This is the first time that host-guest interactions have been introduced into the construction of DNA supraamphiphilic structures, providing a new mode of assembly motifs for DNA assembly. On the basis of this work, Varghese's group further combined the complementary pairing properties of bases and the host-guest interaction to prepare DNA nanogels by using β-CD modified Y-shaped DNA or cruciform DNA and adamantane modified eight-arm polyethylene glycol recognition
[53]. The nanogel has good biocompatibility, excellent cell penetration ability, drug loading performance and DNA addressing performance, which provides the possibility for its application in nanomedicine.
Compared with cyclodextrins, cucurbit [n] uril family is less water-soluble and difficult to derivatize, but it has higher binding capacity with cationic guests. Compared with other cucurbituril molecules, cucurbit [7] uril has excellent molecular properties such as good water solubility, stronger bonding ability and better guest selectivity, while CB [8] and CB [10] with larger cavities can specifically recognize a pair of guest molecules, so the host-guest interaction of cucurbit [n] uril has a wide range of applications in catalysis, material science and other fields.
Liu Simin's group designed two kinds of guest molecules (ferrocene and amantadine) modified by different topological structures (dendrimer and three octadecane chains), and constructed a DNA-CB [7] superamphiphilic compound (D18-CB [7]) with the DNA sequence modified by calabash [7] based on the host-guest interaction between CB and the guest molecules
[54]. It was found that two types of DNA superamphiphilic molecules with different topological structures were assembled into spherical micelles with uniform size (Fig. 4B), which could wrap hydrophobic molecules and load nanoparticles such as gold nanoparticles and functional molecules through DNA complementary pairing. Moreover, the system has competitive guest responsiveness and redox responsiveness (based on the redox properties of ferrocene), which can realize the reversible control of morphology. These results provide a new direction for DNA nanomaterials in drug loading, controlled transport and release.
Based on the fact that CB [8] can recognize a pair of guest molecules (methyl viologen and pyrene), Yang Huanghao's team used pyrene-modified DNA aptamer and methyl viologen-modified octadecyl carbon chain as guest molecules to construct a super-amphiphilic DNA structure under the host-guest interaction of CB [8] and assemble it into vesicles
[55]. Because of the pH response of the system, the drug molecules can be delivered to the targeting site through the specific recognition of the aptamer.
3 Potential applications of DNA-small organic molecule assemblies in biomedical field
DNA-small organic molecule assemblies not only have excellent biocompatibility, low toxicity, good cell permeability, nanoscale size and other characteristics, but also have targeting, efficient loading rate and other properties, which make DNA-small organic molecule assemblies have good applications in drug release, targeted transport, biosensing and other fields.
Tan Weihong's group designed and synthesized a series of amphiphilic DNA hybrids with pyrene-modified DNA sequences and covalently linked two octadecyl chains
[56]. All of these amphiphilic DNA hybrids could assemble into monodisperse spherical micelles, and the size of micelles increased with the increase of DNA chain length. The micelle assembly is size dependent on that cell membrane and can ent the cell by endocytosis. Subsequently, the team further found that Aptamer-Diacyllipids amphiphiles could assemble into spherical micelles (Figure 5A)
[57]. The ATP molecule is used as a target molecule to recognize the conformation of the aptamer so as to change the fluorescence intensity of the assembly, which is used for live cell imaging. These studies provide the basis for biomedical applications of DNA assemblies.
3.1 Drug release
These small molecule modified DNA assemblies can use their own DNA or hydrophobic molecular properties to achieve drug release. In 2013, Barth Barth Él Émy team reported the effects of DNA strands containing different base types and different lipid molecules on DNA-lipid molecular assemblies and their loading capacity, and the release of drug molecules was achieved through complementary pairing of double strands
[58].
3LON-A
15 (a conjugate of a lipid with three alkyl chains and 15 adenine oligonucleotides) is poorly soluble in water, and the other amphiphilic units can self-assemble into micelles of 8 ~ 20 nm. The solubility of
2LON-A
15 in water is less than that of
2LON-T
15, but the assembly of
2LON-A
15 has the strongest ability to load paclitaxel, which can be quickly released by chain hybridization. The assembly can be applied to drug delivery and can release drugs by stimulus response. Subsequently, Zhang's team linked the hydrophobic drug molecule camptothecin to DNA to achieve the preparation of photoresponsive amphiphilic DNA-drug molecule (camptothecin) assembled nanostructures (Figure 5B)
[59]. The system has strong cell absorption capacity and enzymolysis resistance. Under 365 nm light, the 2-nitrobenzyl group connecting the DNA strand is broken, and free camptothecin is released to achieve local light-controlled cytotoxicity, which is expected to provide a reference therapeutic strategy for clinical treatment.
In 2016, Tin and Lo's group combined DNA-lipid amphiphilic self-assembly and DNA origami to construct lipophilic DNA nanocages
[60]. More pronounced cytotoxicity and higher cell death rates in MCF-7 cells were caused by delivery of the drug. In the same year, Varghese's group constructed DNA-PE amphiphilic compounds using phenylene ethynylene (PE) molecules with aggregation-induced luminescence properties, and further assembled them into luminescent vesicles (Figure 5C)
[61]. The assembly has excellent encapsulation ability for both hydrophilic and hydrophobic molecules and good ability to penetrate HeLa cells. By constructing a stable assembly to load functional molecules and deliver them to cells, the efficiency of drug transport is greatly improved.
Combining the conformational change of azobenzene with upconversion nanoparticles will undoubtedly open the door to a new world. In 2019, Ju Huangxian and Liu Ying's team designed an azobenzene-DNA nanopump with more than one conversion nanomaterials for luminescence energy supply by using DNA chains modified by azobenzene molecules, which greatly improved the efficiency of light-controlled drug release
[62]. Under the irradiation of 980 nm laser, the upconversion nanoparticles (UCNPs) emit both ultraviolet and visible light, which promotes the continuous photoisomerization of azobenzene molecules, drives the hybridization and dehybridization of DNA strands, and the continuous photoisomerization of azobenzene promotes the release of drugs loaded in the DNA double helix, thus realizing the efficient release of drugs activated by infrared light.
3.2 Targeted delivery
DNA-organic small molecule assemblies achieve drug encapsulation and intracellular delivery, but the realization of targeted delivery of nanoassemblies is still a great challenge for researchers. Ahn's team reported the targeted delivery of DNA nanoparticles by using the targeting of peptides combined with DNA-organic small molecular assemblies
[63]. The research group used cholesterol-modified DNA strands and complementary strands modified by polypeptide (tLyp-1) to form assembly motifs through Watson-Crick base recognition, and assembled liposome-like nanoparticles. The tLyp-1 polypeptide on the periphery of the nanoparticle can penetrate cells and can be targeted to bind to the surface receptor of breast cancer cells, and the double-stranded DNA can be loaded with doxorubicin, thereby realizing the targeted delivery of anticancer drugs.
Tan Weihong's group also reported amphiphilic compounds with targeting DNA strands covalently linked to difluorodecyl (PF), which can be assembled into stable micelles in aqueous solution
[64]. In addition, PF-DNA micelles (PFDM) can be effectively anchored to the surface of the cell membrane based on hydrophobic interactions, and then PFDM enters the cell through a Lysosome-escape pathway. This PFDM is expected to be used in the fields of biological imaging and biomedicine.
3.3 Biosensing
In 2018, Chai Yaqin's team reported a three-dimensional DNA nanomachine that can precisely control the density and direction of probes and use azobenzene conformational changes to construct, which can be used for rapid single-step sensing of miRNA-21
[65]. Compared with the traditional nanomachine, it has a highly sensitive detection ability for miRNA-21, a marker of breast cancer cells, with a detection limit of 6.6 fM. The nanomachine also has excellent selectivity, stability, reproducibility, and reversibility. This molecular machine shows the great application prospects of the new generation of DNA nanomachines in the field of biology.
In 2020, Professor Tian Leilei's team designed a self-delivered Y-type DNA nanoprobe containing pyrene molecules based on DNA nanotechnology, which realized high specificity and sensitivity imaging of microRNA molecules in living cells
[66].
Although DNA-organic small molecule assemblies have achieved good results in drug release, targeted delivery, biosensing and other fields, they have excellent application prospects, but there are also some challenges. First of all, there are few reports on the types of small organic molecules. Can we expand the types of molecules, especially hydrophobic drug molecules, which are directly linked to DNA through responsive covalent bonds or dynamic bonds, and then released directly after reaching the target site, thus avoiding the problem of low drug loading rate. Secondly, similar to the application of pure DNA nanoassemblies in drug delivery, the stability of DNA-organic small molecule assemblies in vivo is poor, which is easily decomposed by enzymes in serum and excreted by organs such as kidney, so how to improve their stability is also an urgent problem to be solved
[67,68]. Finally, DNA is biocompatible and biodegradable, while whether the non-drug hydrophobic molecules in the hybrid are toxic to organisms and the degree of toxicity are not yet clear, which needs to be studied later. These aspects are not only the challenges faced by the application of DNA-organic small molecule system today, but also the direction for researchers to continue to work hard.
4 Summary and Prospect
In this paper, the assembly behavior of DNA-small organic molecule hybrids in aqueous phase is reviewed, and their potential applications in the biomedical field are discussed. Amphiphilic or super-amphiphilic DNA-organic micromolecule hybrid is constructed by reasonably designing the length of DNA fragments and the arrangement of bases, as well as the topological structure of organic micromolecules, using covalent linkage or host-guest interaction, and forming nanostructures with different assembly morphologies, such as micelles, vesicles, nanosheets and nanobelts, through hydrophobic interaction, π-π stacking and other effects. Reversible regulation of nanostructures can be achieved by external stimuli or DNA conformational changes. At present, nanostructures based on these amphiphilic hybrids are mainly used in drug encapsulation and transportation, controlled release, cell imaging and biological detection.
Although the nanoassemblies based on amphiphilic DNA motifs have good biocompatibility, cell permeability and low cytotoxicity, they are unstable in cells, serum and other environments of organisms, and are easily decomposed by enzymes in serum and excreted by organs such as kidney. At the same time, most of the assemblies do not have targeting function or have poor targeting effect, which greatly reduces the therapeutic effect. Therefore, the construction of DNA assemblies with stable structure, strong targeting ability and excellent cell selectivity is still an important challenge for us, and also an important goal for future development.
National Natural Science Foundation of China(21604066)
National Natural Science Foundation of China(21871216)
Research Project of Hubei Provincial Department of Education(B2016012)
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