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Official websites use. Share sensitive information only on official, secure websites. Hydrogels are crosslinked hydrophilic polymers that can absorb a large amount of water. By their hydrophilic, biocompatible and highly tunable nature, hydrogels can be tailored for applications in bioanalysis and biomedicine. Of particular interest are DNA-based hydrogels owing to the unique features of nucleic acids. Since the discovery of DNA double helical structure, interest in DNA has expanded beyond its genetic role to applications in nanotechnology and materials science. In particular, DNA-based hydrogels present such remarkable features as stability, flexibility, precise programmability, stimuli-responsive DNA conformations, facile synthesis and modification. Moreover, functional nucleic acids FNAs have allowed the construction of hydrogels based on aptamers, DNAzymes, i-motif nanostructures, siRNAs and CpG oligodeoxynucleotides to provide additional molecular recognition, catalytic activities and therapeutic potential, making them key players in biological analysis and biomedical applications. To date, a variety of applications have been demonstrated with FNA-based hydrogels, including biosensing, environmental analysis, controlled drug release, cell adhesion and targeted cancer therapy. We first introduce different strategies for constructing DNA-based hydrogels. Subsequently, various types of FNAs and the most recent developments of FNA-based hydrogels for bioanalytical and biomedical applications are described with some selected examples. Finally, the review provides an insight into the remaining challenges and future perspectives of FNA-based hydrogels. It is because of this significant water content that hydrogels possess a degree of flexibility similar to that of natural tissue. These limitations have prompted scientists to develop more flexible and biocompatible hydrogels. Of particular interest are DNA-based hydrogels for the unique features brought by nucleic acids. DNA has existed in nature for billions of years, and after the discovery of DNA double helical structure by Watson and Crick, the applications of DNA have expanded to nanotechnology and materials science. Compared to antibodies and protein enzymes, DNA possesses enhanced stability under intensive heating, pressure, and chemical processing. The flexibility of DNA hybridization provides a rich library of building blocks for hydrogels. The programmability of DNA strands, which is based on purine and pyrimidine base pairing rules and DNA secondary structures, leads to precisely predicted DNA structure. Under certain conditions, self-assembled DNA hydrogels can be achieved through sequence design, and DNA can also be incorporated into synthetic polymers to form DNA-hybrid hydrogels. Some functional DNAs undergo abrupt conformational changes upon external stimulation, bringing reversible and switchable changes to DNA-based hydrogels. DNA can be synthesized in large quantities by an automated solid-phase technique and can also be modified with many functional groups, such as acrydite, amino, carboxyl and thiol, which can react with other functional moieties. With the development of phosphoramidite chemistry, most DNA modifications can be incorporated by programming a DNA synthesizer for easy preparation and accessibility. The technique of nucleic base modification can introduce multiple functionalities into hydrogels. In spite of their potential usefulness, the idea of DNA-functionalized hydrogels is still a relatively new field, with the first publication having appeared in , 44 and most developments have occurred in just the past ten years. Traditionally, DNA is utilized as carrier for genetic information. However, functional nucleic acids FNAs , such as aptamers, DNAzymes, i-motif structures, antisense DNAs, siRNAs and CpG oligodeoxynucleotides, provide additional molecular recognition, catalytic activities and therapeutic potential, making them key players in biological analysis and biomedical applications. To date, a variety of applications have been demonstrated with FNA-based hydrogels, including biosensing, 49 environmental analysis, 50 controlled drug release, 51 cell adhesion 52 and cancer therapy. We first introduce the different strategies for constructing DNA-based hydrogels. Subsequently, various types of FNAs and the most recent developments of FNA-based hydrogels for bioanalytical and biomedical applications are described using selected examples. Three general strategies were implemented to develop DNA-based hydrogels. The first strategy involves modification of hydrophilic polymer chains with DNA as chain branches and subsequent formation of DNA hydrogels by crosslinking the branches, termed DNA-hybrid hydrogels. The second strategy involves crosslinking of DNA itself to form hydrogels by enzyme ligation, polymerization, hybridization, and specific binding of DNA motifs, termed pure DNA hydrogels. The third strategy involves physical interactions, such as entanglement of DNA or electrostatic interaction between DNA and positively charged polymers to entrap DNA within polymer networks for gene therapy. In this review, we focus on the first two strategies. Further information on all three strategies can be found in several excellent reviews and references highlighted therein. Owning to the unique features of DNA, special consideration has been given to the incorporation of DNA into synthetic polymers to form DNA-hybrid hydrogels, which by the facile molecular engineering of their components, demonstrates such advantages as diversified controllability and multifunctional properties. Then, two types of hydrogels were prepared: i a hydrogel formed by hybridization between an oligoT -derivatized copolymer and an oligoA as a crosslinker Type I in Fig. Since then, using a similar strategy, DNA-PAA copolymers have been used to build various functional hydrogels, which have attracted attention in many fields, especially in stimuli-responsive systems. Hydrogel formation induced by hybrid formation of DNA. A Hydrogel type I via hybridization between oligoT -derivatized water-soluble copolymer with complementary oligoA; B Hydrogel type II via hybridization between oligoA and oligoT attached to the side chains of corresponding copolymers. Adapted with permission from ref. Copyright Elsevier. Instead of using polyacrylamide, some stimuli-responsive polymers can also be employed to construct DNA-polymer hybrid networks to expand the scope of their applications. Temperature-responsive polymer is a major class of stimuli-switchable polymers undergoing reversible temperature-controlled sol-gel phase transitions. At low temperature, water-polymer interaction is strong, and the hydrogel is highly swollen. At temperatures higher than the LCST, hydrogen bonds between polymer and water start to break down, and the hydrogel collapses to interact with itself through hydrophobic interactions. These hydrogels are easy to synthesize, and they can be prepared with controllable sizes and structures. In order to create more stable DNA structures and networks capable of withstanding elevated temperatures, DNA can be chemically modified to improve its thermal stability. After psoralen treatment, the double-stranded core regions were chemically stabilized, while the single-stranded primer region functioned as substrate for DNA processing enzymes, such as Taq DNA polymerase, which is commonly used in polymerase chain reaction PCR. After concentration of the PCR products, this network formed a DNA hydrogel, allowing for novel biotechnological applications, such as a genetically encoded gel for protein production. DNA branches are treated with psoralen to cause covalent interstrand crosslinking. Resulting structures are thermostable and will remain intact under denaturing conditions. Copyright Wiley-VCH. This field could be further expanded by the introduction of many components to afford DNA hydrogel with more functionality and versatility. For example, Xu et al. It should be noted that simply mixing GO dispersion with ssDNA solution only produced heterogeneous hydrogels, mainly owing to the fast binding of ssDNA to GO sheets, which resulted in locally gelated particles. These hydrogels possess high mechanical strength, excellent environmental stability, high dye-adsorption capacity, and self-healing function. Similarly, in , Cheng et al. The two components have no specific interactions when pH is higher than 6. While the pH is lower than 6. Remarkably, the mechanical property of the hydrogel could be adjusted by varying the concentration of hydrogel contents. These TNA hydrogels exhibited biodegradability, extensibility, tissue adhesiveness and hemostatic ability. Notably, this new DNA hydrogel was prepared without chemically modifying DNA or crosslinking by complementary sequences, thus representing a new approach for fabricating DNA-hybrid hydrogels. The multiple steps required for modification of DNA-polymer hybrids have, to some extent, limited their progress. Recently, DNA was reported to form a hydrogel by itself under certain conditions. DNA is a remarkable polymer that can be manipulated by a large number of molecular tools including enzymes. In , Luo and coworkers first reported the construction of a hydrogel entirely made from branched DNA via an enzymatic reaction. These branched DNA stands possess self-complementary sticky ends. Through hybridization of the sticky ends, these branched motifs were first connected to form a 3D network. These DNA hydrogels were biocompatible, biodegradable, and easily molded into desired shapes and sizes. They could be loaded with drugs, proteins and even living cells, which could be released over time upon degradation of the DNA. Subsequently, the same group also successfully incorporated a functional plasmid into the hydrogel and invented a cell-free protein-producing hydrogel system. Examples of pure DNA hydrogels. Copyright Nature Publishing Group. DNA hydrogel made from the three-dimensional assembly of Y-shaped DNA using i-motif structure as the crosslinking element. D Schematic representation of DNA hydrogel formation. The Y-scaffold and linker are designed to crosslink by hybridization of their sticky ends, and accumulating this hybridization will lead to hydrogel formation. Interestingly, these novel hydrogels possessed unique microscale internal structure and unexpected mechanical meta-properties. They behave in a manner that is either liquid- or solid-like, depending on the physical environment. They have liquid-like properties when taken out of water and solid-like properties when in water. The liquid form of the hydrogel can adapt to different shapes of the container. However, it can always rapidly return to its original shape when replaced in water. Such unique meta-properties of the DNA hydrogel may find applications in drug release, cell therapy, electric switches and flexible circuits. Qi et al. Mixing the hydrogels in a tube under rotation produced multi-hydrogel objects with edge lengths ranging from 30 micrometers to a millimeter. Instead of using enzymes to assist the assembly of DNA hydrogels, pure hydrogels can also form by crosslinking DNA building blocks through formation of intermolecular i-motif structures Fig. At neutral pH, no interaction existed within the assembled Y-shaped DNA structure because of electrostatic repulsion. By decreasing the pH to 5, however, these C-rich ends self-assembled to form an i-motif structure, as a result of protonation of the cytosines, in turn resulting in hydrogel formation. Addition of base to the system resulted in an immediate gel-to-sol transition, which occurred within 1 minute. Gold nanoparticles AuNPs , as model indicators, could be trapped and released from the hydrogels following pH changes, demonstrating their potential application in biosensing and drug delivery. The use of i-motif structure as a crosslinker resulted in the stability of these hydrogels, but only at acidic pH, thus preventing their application in physiological conditions. To address this problem, DNA hydrogels were prepared by crosslinking the DNA building blocks by sequence-directed hybridization. It has been well documented that DNA can be precisely designed with specific sequences and self-assemble into two- or three-dimensional nanostructures, 79 - 82 which can then be used as a programmable template to direct the assembly of nanoparticles 83 - 86 or fabrication of nanomotors, nanomachines and nanodevices. Simply mixing the two building blocks at a proper ratio was sufficient to induce the assembly of a Y-scaffold and linker DNA by hybridization of the sticky ends. Accumulating this hybridization will lead to hydrogel formation. Changing the length and composition of sticky ends produces hydrogels with different thermostability. Moreover, they also designed a restriction enzyme sequence domain in the linker DNA structure, bringing specific enzymatic responsiveness of the hydrogels. This research further widened the application conditions of DNA hydrogels. Nucleic acids are fundamental biomacromolecules that function to preserve, transfer, and express genetic information. However, in the s, Cech et al. The following section discusses various kinds of FNA-based hydrogels, as well as their applications, especially in the bioanalytical and biomedical fields. Compared with antibodies, aptamers have many advantages, such as simple synthesis, good stability and design flexibility, making them suitable candidates for DNA hydrogel engineering. Owing to their low K d values, aptamers can specifically recognize their substrates, even at very low concentrations, and undergo structural changes upon binding or dissociation of substrates. These structural changes can stimulate specific physical or chemical interactions within hydrogel systems or circumambient solution systems. In addition, aptamers can be easily conjugated with fluorescent dyes, electrochemical indicators and nanoparticles, thus expanding their applications. Since their first discovery in the s, aptamers have become a focus in bioanalytical, diagnostic and therapeutic applications. Motivated by the special features of aptamers, aptamer-based hydrogels have been developed for biosensing, controlled release, cell adhesion and targeted therapy. By their high target specificity, easy synthesis, low cost, and chemical stability, aptamers have been regarded as promising recognition tools with which to design various sensing systems. Incorporation of aptamers into hydrogels significantly expands the range of stimuli compared with conventional hydrogels. Aptamers that recognize biomolecules can be pretrapped inside hydrogels to further diversify the available stimuli. The design is based on the competitive binding of targets to the trapped DNA aptamers. The first aptamer-based hydrogel was designed to detect adenosine. When P-1 and P-2 were mixed, a fluid state was obtained. Then, the hydrogel was crosslinked by the hybridization of P-1 and P-2 with a rationally designed DNA linker strand S-3 , which contained three functional domains: domain I in pink complementary with S-1 , domain II in green complementary with the last five nucleotides of S-2 , and domain III in purple , an aptamer sequence having seven nucleotides complementary with S In the presence of target adenosine molecules, aptamers competitively bound to targets, but the last five nucleotides of S-2 could not remain hybridized, leading to the breakdown of the crosslinks and the disassembly of the hydrogel within 15min. This disassembly could be exploited to achieve target-responsive payload release. By their optical properties and chemical stability, AuNPs, as visual indicators, were mixed with P-1 and P-2 before gelation. After adding S-3 , the formed hydrogel was immersed in a buffer solution. In the presence of adenosine, the upper buffer solution turned from colorless to red, indicating that the AuNPs had been released into the solution Fig. This result was further confirmed by an absorption test Fig. To further illustrate the versatility of this method, human thrombin aptamer was used to construct the hydrogel. Similar phase transition results were observed in the presence of thrombin. Therefore, the application of this method can be further extended by the introduction of different aptamers, and various analytes can be monitored using these platforms. A Schematic illustration of a hydrogel crosslinked by DNA containing adenosine-binding aptamer as it undergoes gel-to-sol transition upon adding target adenosine. B Photograph of hydrogel having entrapped AuNPs without and with adenosine. C Absorption measurements of AuNPs in the hydrogel system upon addition of adenosine. Reprinted with the permission from ref. Copyright American Chemical Society. Although using AuNPs as indicators in the above method, the sensitivity of this method was still too low for analysis. To solve this problem, Zhu et al. They designed an aptamer-based hydrogel to realize a sensitive visual detection of cocaine. Instead of AuNPs, amylose was chosen as a visual indicator because of its color change from yellow to dark blue in the presence of iodine. In the presence of amylase, amylose would be hydrolyzed to glucose, with no color change in the iodine-glucose solution. Based on these characteristics, amylase was trapped in the DNA-grafted polyacrylamide hydrogel. Because both amylase and amylose are large polymers, they were physically separated by the hydrogel. Thus, amylose with iodine yielded a dark blue color in the buffer solution outside the hydrogel. The crosslinker DNA was a cocaine-binding aptamer that could be competitively removed from the hydrogel by cocaine. Therefore, in the presence of cocaine, the hydrogel disassembled and released amylase to the buffer solution. Amylose was then digested by amylase, and the dark blue color disappeared. Importantly, it was not necessary for the entire gel to completely dissolve, as long as sufficient amylase was released to the solution, causing the color to weaken. Results demonstrated that this platform could detect less than 20 ng cocaine in 10 min with the naked eye. Moreover, in order to perform a quantitative analysis, the same group introduced a glucose meter to the hydrogel detection system. As shown in Fig. After adding strand S-6 to form the hydrogel, glucoamylase was trapped inside the hydrogel and physically separated from its substrate, amylose, which was in the solution outside the hydrogel. In the presence of target cocaine, strand S-6 specifically bound with targets to form target-aptamer complexes, leading to breakdown of the hydrogel and release of glucoamylase, which catalyzed the hydrolysis of amylose to produce a large amount of glucose for quantitative readout by the PGM. The method enabled selective analysis of cocaine with a detection limit corresponding to 3. Since different aptamers can be used for construction, it is possible to extend this simple, portable, inexpensive and quantitative hydrogel detection method to a range of nonglucose targets. The hydrogel with trapped glucoamylase is formed by hybridization of the aptamer and its partially complementary DNA polymer strands S-4 and S The aptamers specifically identify the target cocaine to form target-aptamer complexes, leading to breakdown of the hydrogel and release of glucoamylase, which catalyzes the hydrolysis of amylose to produce a large amount of glucose for quantitative readout by the glucometer. The prepared hydrogel was kept in the hydrogel reservoir of the V-chip Fig. The aptamer-target complexes formed after target cocaine was added to the reservoir, leading to dissociation of the hydrogel and release of the encapsulated Au Pt NPs into the supernatant solution Fig. By sliding up the V-chip, three connected horizontal channels were formed Fig. Under negative pressure, the supernatant containing the released Au Pt NPs was drawn into the first channel green. H 2 O 2 and the indicator red ink were injected into the second channel yellow and the third channel red , respectively. By further sliding up the V-chip, the supernatant, H 2 O 2 and red ink were loaded in six independent parallel connected vertical channels Fig. The moving distance in each ink bar within a specified time was independently correlated with the concentration of the Au Pt NPs catalyst, which, in turn, was proportional to target concentration. Owing to high sensitivity, selectivity, portability, and quantitative visual detection, the V-chip method has potential applications in POCT, environmental safety and food quality assurance. Schematic illustration of the Au Pt NPs-encapsulated target-responsive hydrogel with a V-chip readout for visual quantitative detection. Dual response was also possible by crosslinking the hydrogel with two types of aptamers, allowing for the design of logic gate systems. Aptamer-based logic gates that respond to multiple targets, or one target and some environmental stimulus, such as pH, have been described by several groups. In order to visualize the gel-sol transition, the authors pretrapped AuNPs into the hydrogel as indicators. In the case of one input ATP or cocaine , two of the three hybridizations was interrupted, but the three strands remained linked, and the hydrogel stayed intact Fig. When both cocaine and ATP were introduced as inputs, the hydrogel underwent a gel-sol transition, and the entrapped AuNPs were then released to buffer solution Fig. As a result, the buffer solution turned from colorless to red, which could be easily detected with the naked eye. As such, either of the inputs could decompose the hydrogel and release the AuNPs. The hydrogel dissociated only when both cocaine and ATP were present. Adapted with the permission from ref. Copyright Royal Society of Chemistry. Other than small organic molecules, aptamers able to recognize proteins are also implemented in hydrogels for detection of protein or virus. These complexes were then incorporated into hydrogels via free radical polymerization in which thrombin served as a crosslinker imprinted in the hydrogel. Removal of the imprinted thrombin dissolved partial crosslinkers, resulting in a swelling response of the hydrogel with increased length. Such changes in hydrogel length were reversible by reintroducing target thrombin into the hydrogel such that shortening of the length was dependent on the amount of thrombin introduced. Removal of proteins from the hydrogel resulted in visible length increase of hydrogel in the capillary, while reintroduction of proteins gave a shrinking response. It is remarkable that volume changes in this type of hydrogel were visible to the naked eye down to femtomolar concentrations of proteins. Furthermore, specific recognition could even be maintained in biological matrices, such as urine and tears. Specifically, apple stem pitting virus ASPV , which is a filamentous virus with a capsid comprised of MT32 proteins, was chosen as a target. The mixture of aptamer against MT32 with the virus extract was prepared as the prehydrogel solution. Additional monomers were added to the prehydrogel solution and then cast onto the elastomer grating micromolds for gelation. Thus, the virus sample was imprinted into the grating-patterned hydrogel. Removal or rebinding of the virus caused the expansion or contraction of hydrogel, and the hydrogel's change of volume was then detected by passing a laser light through the hydrogel and measuring the 1D diffraction patterns with a ruler that could be read by the naked eye. In another example, aptamer-based hydrogels were immobilized on quartz crystal microbalance QCM for rapid, sensitive and specific detection of influenza virus H5N1. Hydrogels are one of the most appealing polymeric materials for preparing capture-and-release systems for target molecules. Such systems impact drug development and regenerative medicine. The capture and controlled release of target molecules are critical steps in designing a hydrogel system for drug delivery. Because most hydrogels have high water-absorbing abilities, targets drugs, in most cases can be easily released in a short time without modification. Therefore, to slow the release process and prolong drug action, different strategies have been adopted, either by modulating the interaction between the target and hydrogel matrix or by modifying the hydrogel network. In order to test the sustained release of protein, the hydrogel was immersed in a release medium. These results suggested that the aptamer-functionalized hydrogel was successful in sustained protein release through the specific binding between aptamer and its target. Nevertheless, it remains necessary to develop a controlled release system allowing for the triggered release at a defined time point. To accomplish this, the strand displacement technique has been used to manipulate hydrogel structural changes. Using this strategy, Mi and coworkers constructed a reversible hydrogel for capture and release of protein. The capture of thrombin was achieved by the strong interaction between aptamer and thrombin. The hydrogel was formed by mixing the DNA-functionalized polyacrylamide with thrombin-bound linker strands. Therefore, thrombin was loaded and retained in hydrogel through aptamer binding. The crosslinking of hydrogel was found to be reversible when a fully complementary sequence of linker strand was added to the system, leading to gel dissolution and thrombin release. Later, the same group developed an aptamer-based hydrogel to separate a specific target from a mixed system. Indeed, the capture of biomolecules from real samples still remains challenging, given the complexity of virtual environments. Thus, effective capture of biomolecules from fluid mixtures is vital for applications ranging from target characterization in biochemistry to environmental analysis and biomedical diagnostics. Shastri et al. In this system, the selected aptamer and hydrogel were both pH-sensitive. The aptamer specifically bound to thrombin at pH range , but was reversibly denatured and lost affinity for thrombin at low pH Fig. Similarly, a pH-sensitive and biocompatible poly acrylamide-co-acrylic acid hydrogel was chosen as the dynamic arm able to undergo significant volumetric changes at pH 4. The synchronization of reversible aptamer-thrombin binding and hydrogel volume changes provided the coordinated transport of thrombin between two environments for effective extraction of biomolecules. When the pH value of the bottom layer shifted between 3. In basic condition, the system returned to initial states, ready for another round of target capture. The reversibility of hydrogel volume change and aptamer folding allowed for continuous separation of targets for multiple rounds, ensuring the sufficient capture and detection of target molecules. Indeed, the recovery test showed that nearly Further data demonstrated the selectivity of this system. The target protein thrombin could be selectively captured from a mixture of thrombin and transferrin, thrombin and BSA, or human serum containing thrombin, leaving the interfering protein in the top layer of fluid. These results showed high performance on concerted capture-and-release of target molecules from a fluid mixture by this chemo-mechanical sorting system. Scheme of a hybrid microfluidic system for biomolecule capture-and-release. C A cross-sectional view of the biphasic microfluidic chamber under constant laminar flow with aptamer-decorated microstructures. Reprinted with permission from ref. Regulating cell-material surface interaction is significant for a variety of biological and biomedical applications, such as biological separation, tissue repair and wound healing. The high-affinity and -specificity interactions between aptamers and receptors on the cell surface provide an effective means of cell adhesion. Aptamer-functionalized hydrogels were constructed for dynamic control of cell adhesion. In order to regulate cell behavior, Chen et al. In addition, attenuated cell adhesion could be achieved by inactivation of aptamers using their complementary DNAs. Besides using strand displacement, restriction endonuclease was also employed in hydrogels for cell detachment. Recently, Li et al. Upon addition of a secondary CS strand S , the fully complementary sequence of aptamer, a strand displacement procedure was triggered, and the conformation change of aptamer induced the release of aptamers and target cells. The whole procedure of cell capture and release took place under physiological conditions without any destructive factor. Hydrogel functionality is regenerable, suggesting its potential in numerous biological and biomedical applications. Later, cell attachment of hydrogel was further enhanced by implementing polyvalent aptamer, in which multiple aptamers were hybridized with one backbone as side units for polyvalency of target cell binding, leading to more cell binding with equal amounts of surface reaction sites. Schematic illustration demonstrating the use of a programmable hydrogel for cell capture-and-release. A Transformation of the aptamer. B Cell capture-and-release by strand displacement strategy. Hybridization with the primary CS enables the display of the aptamer for cell capture. The secondary CS competes against the primary CS to hybridize and release the aptamer from the hydrogel, resulting in cell release. More recently, Li et al. This intramolecular hybridization of S led to an inert state of aptamer, which inhibits cell adhesion. However, upon addition of unblocking sequence strand S , the cell adhesion function was activated through the hybridization between S and the S blocking domain. Next, in order to realize cell detachment, a recovering sequence strand S was applied to neutralize and dissociate the S sequence from the blocking domain, returning S to its encrypted state and returning the hydrogel to its inert state so that it would be available for a new round of cell capture and release. Thus, the cell adhesion function of hydrogels can be modulated by using unblocking and recovering sequences Fig. Moreover, since molecular reconfiguration does not induce any loss or cleavage of ligand from the hydrogel, the cell adhesion function can be reversibly controlled for multiple cycles by treatment of S and S sequences. A Schematic illustration of structural changes during molecular reconfiguration. B Schematic illustration of the remodeling of the S -functionalized hydrogel during hybridization reactions. The function of the hydrogel is determined by the active and inert states of S , respectively. S is the unblocking sequence, and S is the recovering sequence. Current cancer therapy, including chemotherapy and radiotherapy, often lacks tumor cell specificity, putting cancer patients at risk for severe toxic effects. Recently, the active and cell-specific targeting of nanomaterials has begun to represent a potentially powerful technology in cancer treatment. Therefore, combining the unique features of hydrogels and specific recognition ability of aptamers will allow for the design of aptamer-based hydrogels with decreased side effects and enhanced therapeutic efficacy. The first example is near-infrared light-responsive core-shell nanohydrogels for targeted drug delivery. In one part, acrylamide monomers and acrydite-modified strand A S were first linked with a methacryl group on Au-Ag NRs to form a multiple linear polyacrylamide polymer conjugate. In another part, acrydite-modified strand B S and acrydite-modified aptamer sequence S were incorporated to obtain polymer chains. The crosslinker DNA strand S , which hybridized with strands S and S , resulted in the formation of core-shell nanohydrogels. When the temperature was higher than DNA melting temperature, double-stranded DNA dissociated, resulting in breakdown of the nanohydrogels. Meanwhile, the payload of anticancer drugs Dox as a model was released to generate therapeutic effect. This study takes advantage of the aptamer as a recognition element and the nanohydrogels as a drug carrier, demonstrating the potential of this system for targeted cancer therapy. Schematic illustration of aptamer-functionalized core - shell nanohydrogels for targeted chemotherapy. The use of pure DNA molecules as building blocks for hydrogel construction has attracted substantial attention in the form of smart devices and precisely defined nanostructures at the nanometer scale for sensing, drug delivery and cancer therapy. YMA serves as a building unit with three sticky ends. YMB has one sticky end and an aptamer moiety, which serves as both a blocking unit to inhibit the extension of nanoparticles and a targeting unit to recognize specific cancer cells. LK is a linear duplex DNA with two sticky ends. Hybridization of the sticky ends of monomers and LK leads to nanohydrogel formation. To design stimuli-responsive DNA nanohydrogels for targeted gene therapy, different functional elements, including antisense oligonucleotides capable of inhibiting cell proliferation, DNAzymes capable of inhibiting cell migration, and aptamers capable of targeting specific cancer cells and disulfide linkages, can be incorporated into different building units. The designed nanohydrogels were stable during blood circulation and were efficiently cleaved in the intracellular reductive environment, resulting in the dissociation of nanohydrogels and release of multiple therapeutic genes. After aptamer incorporation, the synthesized aptamer-based nanohydrogels could strongly inhibit cell proliferation and migration of target A cells, but not control cells, suggesting the potential for targeted gene regulation therapy. Schematic illustration of stimuli-responsive DNA nanohydrogel formation. The Y-shaped monomers YMA and YMB and linker LK are designed to crosslink by hybridization of their sticky end segments black lines , leading to nanohydrogel formation. Catalytic nucleic acids DNAzymes or ribozymes represent sequence-specific nucleic acids mimicking the function of native enzymes. The first type of ribozymes discovered was a self-splicing RNA. Recently, Willner's group reported a switchable catalytic DNA hydrogel. In , Lin et al. Gelation was achieved by mixing the two polymers and the hybridization between two strands. AuNPs, as colorimetric indicators, were also encapsulated inside the matrix before gelation. This method can be further extended to other metal ion sensors by using corresponding DNAzymes. More recently, Willner and coworkers reported the programmed dissolution of three different metal ion-dependent DNAzyme hydrogels for activation of an enzyme cascade. In the presence of the respective ions, the substrates of the corresponding DNAzymes were cleaved, leading to the dissolution of hydrogels and the release of enzymes. By mixing different DNAzyme-bridged hydrogels, selective and programmed hydrogel dissolution and enzyme release could be achieved, thus activating bi- or trienzyme cascades. Natural Watson-Crick base pairs play a critical role in double helical nucleic acids which are responsible for the storage and transfer of genetic information. Although natural base pairs have been amazingly sophisticated throughout the long history of evolution, synthetic chemists have devoted considerable efforts in recent decades to create alternative base pairing systems to extend the information-encoding capabilities of nucleobases. Most of these new base pairings were designed by rearranging the hydrogen-bonding patterns using hydrophobic interactions or metal coordination. It is well known that metal coordination plays various roles in maintaining and stabilizing biologically important structures in terms of molecular recognition and catalytic activity. Recently, base pairing based on metal ion coordination, termed metallo-base pairs, has been developed and has gained increasing attention. Conjugation of such metallo-base pairs into hydrogels has also attracted considerable attention for detection and removal of hazardous ions. The fluorescence change could be easily observed with a detection limit of 10 nM in 50 mL water. The combination of high selectivity of T-Hg-T base pairs and high binding affinity of gel matrix provided high detection sensitivity and adsorption capacity. Later, the same group made further efforts to optimize this system, and detection sensitivity was enhanced by manipulating electrostatic interactions among SYBR Green I, DNA and hydrogel backbone. In another application taking advantages of T-Hg-T base pairs in the construction of hydrogel, Ye et al. The shift value could be used for quantitative analysis of the target metal ions. Depending on their shrinkage, the color and the diffraction peak of CPCHs underwent a blue shift. The fluorescence property of the hydrogel was preserved when undergoing thermally reversible hydrogel solution transition, indicating good thermostability of this system. The i-motif structure is a DNA quadruplex structure which can form in sequences rich in cytosine. Several applications in DNA nanotechnology have emerged owing to its unique properties. Therefore, introduction of i-motif structure into DNA hydrogels will expand its biosensing and biomedical applications. In , Liu and coworkers reported a pH-responsive DNA hydrogel using i-motif structure as a crosslinker. Meanwhile, as a thermosensitive polymer, pNIPAM endowed the hydrogel with temperature-controlled effects. Such pH-triggered thermosensitive hydrogels paved the way for the construction of sensors and drug delivery systems. Apart from thermosensitivity, DNA hydrogels can be tailored with shape-memory properties. One was a C-rich sequence corresponding to i-motif structures as the stimuli-responsive element strand S , and the other was a set of self-complementary sequences for duplex formation as the shape-memory element strand S In their design, C-rich strands assembled into i-motif structure at pH 5. At pH 8. By repeatedly switching pH between 5. Schematic illustration of a pH-switchable, shape-memory DNA hydrogel. The separated hydrogel triangular structure is subjected to pH 8. Changing pH to 5. Therapeutic oligonucleotides include a wide range of nucleic acids with different functional properties, such as antisense, RNA interference and immunorecognition. First discovered by Fire et al. It is easy to incorporate therapeutic oligonucleotides into DNA-based hydrogels based on their nucleic acid nature. Hong et al. Different combinations of siRNA units led to the formation of different types of products. The siRNA microhydrogels were condensed by a cationic polymer, linear polyethylenimine LPEI , leading to the formation of compact and stable nanoparticles below nm in size with enhanced stability and higher cellular uptake efficiency. In another work by Hong et al. Another widely applied therapeutic oligonucleotide is unmethylated cytosine-phosphate-guanine dinucleotides CpG , a potent activator of innate and acquired immune responses. The CpG sequence is prevalent in bacterial genomes, while only occasionally seen in mammalian genomes. Therefore, it is considered to be a signal of pathogen invasion by the immune system, which is recognized by Toll-like receptor 9 TLR9 , followed by induction of immune response. DNA-based hydrogels can also enhance the therapeutic efficacy of chemotherapy and immunotherapy. In , Nishikawa et al. Dox was then incorporated into the hydrogel and slowly released with hydrogel degradation. However, the administration of these bulky hydrogels required surgical incision, or breaking them down into fragments small enough for injection. Furthermore, the contaminating ligase had the potential of causing unwanted side effects, including anaphylactic shock. To address these issues, they further developed an injectable, ligase-free and immunomodulatory DNA hydrogel for antigen delivery. These hydrogels were easily injected using a fine gauge needle, and gelation occurred almost instantly following injection. Removal of CpG motifs from the hydrogel resulted in a sharp decrease in immune response, indicating the significance of immunostimulation by CpG DNA hydrogel. Advances in biochemistry and materials science have sparked interest in the development of various biocompatible materials for bioanalytical and biomedical applications. Based on their high biocompatibility, high flexibility, low toxicity and highly tunable nature, hydrogels are promising materials in bioanalytical and biomedical applications. On the other hand, functional nucleic acids FNAs , including aptamers, DNAzymes, i-motif structures, siRNAs and CpG motifs, provide additional molecular recognition, catalytic activities, and therapeutic potential, affording potential applications for diagnosis and therapeutics. Incorporation of FNAs into hydrogel systems can be manipulated with additional properties, significantly expanding the applications of DNA-based hydrogels, as demonstrated by the selected examples described in this review. Thus far, FNA-based hydrogels have been implemented to design sensors, separation platforms, cell adhesion platforms, controlled drug delivery and targeted cancer therapy methods. In addition, it should be noted that the use of FNA-based hydrogels for novel applications, such as molecular logic gates, mechanical actuators, and portable detection devices, has been achieved. Although these studies are still in the preliminary stage, they represent promising potential uses of these hydrogels. However, to further move the applications of FNA-based hydrogels forward, several challenges must be addressed. First, colorimetric visual detection methods based on hydrogel phase changes provide simple and rapid detection of various targets, but the problems of sensitivity and quantification have limited their applications. Incorporation of enzyme-catalyzed signal amplification mechanisms e. Furthermore, the detection of targets in real samples remains challenging, given the complexity of virtual environments. Therefore, development of simple and sensitive sensors capable of analyzing targets in complex biological samples should be a prospective direction for hydrogel-based sensors. Second, some FNA-based hydrogel systems lack efficient and precise release mechanisms, leading to premature release. The design of dual-responsive hydrogels can be used for precisely controlled cargo release. For example, incorporation of pNIPAM into polyacrylamide gel will give the hydrogel additional thermosensitive property. In addition, light-sensitive property can be regulated by incorporating azobenzenes, and pH-sensitive property can be achieved by i-motif structure. Other types of stimuli, such as NIR irradiation and magnetic fields, can also be explored. In dual-responsive hydrogels, hydrogel transitions can be triggered only in the presence of both stimuli, thus leading to more accurate operation of FNA-based hydrogel systems. Third, the bulky size of some FNA-based hydrogels curtails their biomedical applications. The development of methods for preparation of nanohydrogels and effective delivery of nanohydrogels into cells will expand the scope of in vivo applications. Finally, although FNA-based hydrogel systems appear to hold promise for controlled release and targeted cancer therapy, some issues remain to be resolved, such as poorly understood pharmacokinetics, long-term toxicity and off-target effects. To realize the full potential and overcome the challenges of such hydrogels, it is necessary to perform more stringent in vivo studies to further understand the behavior of these hydrogels. Furthermore, in-depth studies in animal models for the evaluation of safety and efficacy of these hydrogels will lay the foundation for further clinical applications. Future efforts should focus on improving these hydrogels for clinical use. Through collective efforts, we believe that the integration of further developments in materials science and nanotechnology will promote the development of FNA-based hydrogels for a variety of practical bioanalytical and biomedical applications. This section collects any data citations, data availability statements, or supplementary materials included in this article. As a library, NLM provides access to scientific literature. Chem Soc Rev. Published in final edited form as: Chem Soc Rev. Find articles by Juan Li. Find articles by Liuting Mo. Find articles by Chun-Hua Lu. Find articles by Ting Fu. Find articles by Huang-Hao Yang. Find articles by Weihong Tan. PMC Copyright notice. The publisher's version of this article is available at Chem Soc Rev. Open in a new tab. Similar articles. Add to Collections. Create a new collection. Add to an existing collection. Choose a collection Unable to load your collection due to an error Please try again. Add Cancel.

Everything You Should Know About a Hair Strand Drug Test

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Persistent drug misusers beware: hair drug testing is considered the gold standard when it comes to proving drug abuse. It can effectively confirm long-term exposure to drugs over a defined period of time depending on the length of hair collected. The reason is that after a drug has been absorbed into the bloodstream, it is broken down in the liver to produce specific metabolites. These metabolites then become embedded into the growing hair shaft from blood supplying the hair follicle. And they remain in the hair as it grows. It may be able to effectively confirm long-term exposure to drugs, but hair strand analysis cannot show recent drug history. This is because it can take between 7—10 days for the hair containing the drug to grow from the follicle to above the scalp. However, in this case, other analytical sampling methods could be used, which have a much smaller window of detection. For example, urine and oral fluid tests can give positive results for drugs after only a matter of hours. In addition, it could be transferred by direct contamination such as by hands. To avoid any such false positive results, AlphaBiolabs chemically washes each hair sample three times to remove or reduce any drug present prior to analysis. The washing solution can also be analysed if required. For example, if you admit to being surrounded by cannabis smokers, the washing solution could be used to back up the test results. However, any drug you have taken directly will be found within the hair shaft itself. This means that any environmental exposure to cannabis can be differentiated from ingested cannabis. However, before you reach for the shaver, be aware that body hair can also be tested for drugs. In the case of no, or insufficient, head hair, alternative collection sites would be considered including pubic, underarm, leg — and if male: chest and beard hair. The growth rate of hair from these alternate sites differs from head hair, which means that body hair cannot be used to determine a specific timeframe of drug use. However, it can provide up to a month overview. If your hair sample collection is not witnessed then there are several options open to you. It is possible to submit hair samples for testing for your peace of mind. This means that the results are not legally binding and could not be used in a court of law. However, it does make it easier to try and fool the testing laboratory. However, all hair samples are visually inspected on arrival at our lab. Fake hair would be rejected at this stage. In addition, our trained sample collectors ensure that the person undergoing the testing is the correct individual. Identification is checked and photographs taken. A company sample collector would also ensure that the hair sample is taken from the correct area. It needs to be cut from the highest point of the scalp the vertex as this region is associated with least variation in growth rates. Ideally, the sample needs to contain around individual strands. Excessive shampooing, some cosmetic treatments and the use of thermal straighteners may reduce drug concentrations in hair to varying degrees. Some detoxification shampoos are designed specifically to permanently reduce toxin levels in the hair strand so they fall below detectable levels in a laboratory hair test. By penetrating deeply into the hair strand these shampoos claim to remove all traces of accumulated chemical deposits including drug metabolites. Various chemicals used in other hair treatments such as dyeing, bleaching, perming and relaxing may also interfere with drug test results and could possibly help you pass a test. Be aware that laboratory tests that study hair samples for the presence of drug metabolites are extremely reliable. Because the metabolites pass from the bloodstream into your hair follicles this evidence remains locked in the strand of hair as it grows. The extent of any loss will depend on the cosmetic treatment used and the drug present. Are you willing to risk it? So, can a hair drug test result be falsified? Not at AlphaBiolabs. The accuracy of any hair drug analysis depends on both the sampling procedure and the laboratory techniques employed. An accredited drug testing company ensures that the samples are analysed using state-of-the-art equipment to quickly identify specific illegal drugs, even those that are new to the market. Our trained sample collectors will ensure that the correct individual is undergoing testing, and that the hair sample is real and indeed human! If you have plenty of time on your hands, the only sure way of passing a hair drug test is via a natural detox. You might enjoy clean living? For expert advice on hair testing and other drug testing solutions , please call or email us at info alphabiolabs. Your email address will not be published. We look at some of the common methods used by drug users to try and make sure the results come back in their favour. We provide testing to the legal profession, corporations and members of the public. Skip to content Order a Drug Test AlphaBiolabs is an accredited laboratory offering a range of drug testing services. More Info. Leave a Reply Cancel reply Your email address will not be published. Related articles…. Can you refuse a drugs test? Read more. The ways people try to cheat a drugs test We look at some of the common methods used by drug users to try and make sure the results come back in their favour. Share this page. Your test is in safe hands. The role of repeat alcohol testing in Family Court.

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