An Aptamer Cross-Linked Hydrogel as a Colorimetric Platform for Visual Detection

Label/immobilization-free Cas12a-based electrochemiluminescence biosensor for sensitive DNA detection

Electrochemiluminescence (ECL) is one of the most sensitive techniques in the field of diagnostics. However, they typically require luminescent labeling and electrode surface biological modification, which is a time-consuming and laborious process involving multiple steps and may also lead to low reaction efficiency. Fabricating label/modification-free biosensors has become one of the most attractive parts for simplifying the ECL assays. In this work, the ECL luminophores carbon dots (CDs) were encapsulated in DNA hydrogel in situ by a simple rolling circle amplification (RCA) reaction. Upon binding of the target DNA, active Cas12a induces a collateral cleavage of the hydrogel's ssDNA backbone, resulting in a programmable degradation of the hydrogel and the release of CDs. By directly measuring the released CDs ECL, a simple and rapid label/modification-free detection of the target HPV-16 was realized. It is noted that this method allowed for 0.63 pM HPV-16 DNA detection without any amplification step, and it could take only ∼60 min for a fast test of a human serum sample. These results showed that our label/modification-free ECL biosensor has great potential for use in simple, rapid, and sensitive point-of-care (POC) detection.

Geometrically Scalable Iontronic Memristors: Employing Bipolar Polyelectrolyte Gels for Neuromorphic Systems

Iontronics that are capable of mimicking the functionality of biological systems within an artificial fluidic network have long been pursued for biomedical applications and ion-based intelligence systems. Here, we report on facile and robust realization of iontronic bipolar memristors featuring a three-layer polyelectrolyte gel structure. Significant memristive hysteresis of ion currents was successfully accomplished, and the memory time proved geometrically scalable from 200 to 4000 s. These characteristics were enabled by the ion concentration polarization-induced rectification ratio within the polyelectrolyte gels. The memristors exhibited memory dynamics akin to those observed in unipolar devices, while the bipolar structure notably enabled prolonged memory time and enhanced the ion conductance switching ratio with mesoscale (10-1000 μm) geometry precision. These properties endow the devices with the capability of effective neuromorphic processing with pulse-based input voltage signals. Owing to their simple fabrication process and superior memristive performance, the presented iontronic bipolar memristors are versatile and can be easily integrated into small-scale iontronic circuits, thereby facilitating advanced neuromorphic computing functionalities.

Aptamer-based targeted delivery systems for cancer treatment using DNA origami and DNA nanostructures

Due to the limitations of conventional cancer treatment methods, nanomedicine has appeared as a promising alternative, allowing improved drug targeting and decreased drug toxicity. In the development of cancer nanomedicines, among various nanoparticles (NPs), DNA nanostructures are more attractive because of their precisely controllable size, shape, excellent biocompatibility, programmability, biodegradability, and facile functionalization. Aptamers are introduced as single-stranded RNA or DNA molecules with recognize their corresponding targets. So, incorporating aptamers into DNA nanostructures led to influential vehicles for bioimaging and biosensing as well as targeted cancer therapy. In this review, the recent developments in the application of aptamer-based DNA origami and DNA nanostructures in advanced cancer treatment have been highlighted. Some of the main methods of cancer treatment are classified as chemo-, gene-, photodynamic- and combined therapy. Finally, the opportunities and problems for targeted DNA aptamer-based nanocarriers for medicinal applications have also been discussed.

DNA Droplets: Intelligent, Dynamic Fluid

Breathtaking advances in DNA nanotechnology have established DNA as a promising biomaterial for the fabrication of programmable higher-order nano/microstructures. In the context of developing artificial cells and tissues, DNA droplets have emerged as a powerful platform for creating intelligent, dynamic cell-like machinery. DNA droplets are a microscale membrane-free coacervate of DNA formed through phase separation. This new type of DNA system couples dynamic fluid-like property with long-established DNA programmability. This hybrid nature offers an advantageous route to facile and robust control over the structures, functions, and behaviors of DNA droplets. This review begins by describing programmable DNA condensation, commenting on the physical properties and fabrication strategies of DNA hydrogels and droplets. By presenting an overview of the development pathways leading to DNA droplets, it is shown that DNA technology has evolved from static, rigid systems to soft, dynamic systems. Next, the basic characteristics of DNA droplets are described as intelligent, dynamic fluid by showcasing the latest examples highlighting their distinctive features related to sequence-specific interactions and programmable mechanical properties. Finally, this review discusses the potential and challenges of numerical modeling able to connect a robust link between individual sequences and macroscopic mechanical properties of DNA droplets.

Hydrogel-Based Biosensors

There is an increasing interest in sensing applications for a variety of analytes in aqueous environments, as conventional methods do not work reliably under humid conditions or they require complex equipment with experienced operators. Hydrogel sensors are easy to fabricate, are incredibly sensitive, and have broad dynamic ranges. Experiments on their robustness, reliability, and reusability have indicated the possible long-term applications of these systems in a variety of fields, including disease diagnosis, detection of pharmaceuticals, and in environmental testing. It is possible to produce hydrogels, which, upon sensing a specific analyte, can adsorb it onto their 3D-structure and can therefore be used to remove them from a given environment. High specificity can be obtained by using molecularly imprinted polymers. Typical detection principles involve optical methods including fluorescence and chemiluminescence, and volume changes in colloidal photonic crystals, as well as electrochemical methods. Here, we explore the current research utilizing hydrogel-based sensors in three main areas: (1) biomedical applications, (2) for detecting and quantifying pharmaceuticals of interest, and (3) detecting and quantifying environmental contaminants in aqueous environments.

DNA Nanotechnology-Based Supramolecular Assemblies for Targeted Biomedical Applications

DNA is a polyanionic, hydrophilic, and natural biopolymer that offers properties such as biodegradability, biocompatibility, non-toxicity, and non-immunogenicity. These properties of DNA as an ideal biopolymer offer modern-day researchers' reasons to exploit these to form high-order supramolecular assemblies. These structures could range from simple to complex and provide various applications. Among them, supramolecular assemblies like DNA hydrogels (DNA-HG) and DNA dendrimers (DNA-DS) show massive growth potential in the areas of biomedical applications such as cell biology, medical stream, molecular biology, pharmacology, and healthcare product manufacturing. The application of both of these assemblies has seen enormous growth in recent years. In this focused review on DNA-based supramolecular assemblies like hydrogels and dendrimers, we present the principles of synthesis and characterization, key developments with examples and applications, and conclude with a brief perspective on challenges and future outlook for such devices and their subsequent applications.

Putting DNA to Work as Generic Polymeric Materials

DNA is a true polymer that stores the genetic information of an organism. With its amazing biological and polymeric characteristics, DNA has been regarded as a universal building block for the construction of diverse materials for real-world applications. Through various approaches including ligation, polymerization, chemical crosslinking, and physical crosslinking, both pure and hybrid DNA gels have been developed as generic materials. This Review discusses recent advances in the construction of DNA-based networks without considering any of DNA's genetic properties. In addition, we highlight the biomedical and non-biomedical applications of DNA as generic materials. Owing to the superb molecular recognition, self-assembly, and responsiveness of DNA, a mushrooming number of DNA materials with various properties have been developed for general utilization.

Smart and Functionalized Development of Nucleic Acid-Based Hydrogels: Assembly Strategies, Recent Advances, and Challenges

Nucleic acid-based hydrogels that integrate intrinsic biological properties of nucleic acids and mechanical behavior of their advanced assemblies are appealing bioanalysis and biomedical studies for the development of new-generation smart biomaterials. It is inseparable from development and incorporation of novel structural and functional units. This review highlights different functional units of nucleic acids, polymers, and novel nanomaterials in the order of structures, properties, and functions, and their assembly strategies for the fabrication of nucleic acid-based hydrogels. Also, recent advances in the design of multifunctional and stimuli-responsive nucleic acid-based hydrogels in bioanalysis and biomedical science are discussed, focusing on the applications of customized hydrogels for emerging directions, including 3D cell cultivation and 3D bioprinting. Finally, the key challenge and future perspectives are outlined.

Freezing-Assisted Conjugation of Unmodified Diblock DNA to Hydrogel Nanoparticles and Monoliths for DNA and Hg2+ Sensing

Acrydite-modified DNA is the most frequently used reagent to prepare DNA-functionalized hydrogels. Herein, we show that unmodified penta-adenine (A₅ ) can reach up to 75 % conjugation efficiency in 8 h under a freezing polymerization condition in polyacrylamide hydrogels. DNA incorporation efficiency was reduced by forming duplex or other folded structures and by removing the freezing condition. By designing diblock DNA containing an A₅ block, various functional DNA sequences were attached. Such hydrogels were designed for ultrasensitive DNA hybridization and Hg²⁺ detection, with detection limits of 50 pM and 10 nM, respectively, demonstrating the feasibility of using unmodified DNA to replace acrydite-DNA. The same method worked for both gel nanoparticles and monoliths. This work revealed interesting reaction products by exploiting freezing and has provided a cost-effective way to attach DNA to hydrogels.

Reversible Control of Gelatin Hydrogel Stiffness by Using DNA Crosslinkers*

Biomaterials with dynamically tunable properties are critical for a range of applications in regenerative medicine and basic biology. In this work, we show the reversible control of gelatin methacrylate (GelMA) hydrogel stiffness through the use of DNA crosslinkers. We replaced some of the inter-GelMA crosslinks with double-stranded DNA, allowing for their removal through toehold-mediated strand displacement. The crosslinks could be restored by adding fresh dsDNA with complementary handles to those on the hydrogel. The elastic modulus (G') of the hydrogels could be tuned between 500 and 1000 Pa, reversibly, over two cycles without degradation of performance. By functionalizing the gels with a second DNA strand, it was possible to control the crosslink density and a model ligand in an orthogonal fashion with two different displacement strands. Our results demonstrate the potential for DNA to reversibly control both stiffness and ligand presentation in a protein-based hydrogel, and will be useful for teasing apart the spatiotemporal behavior of encapsulated cells.

Control of capillary behavior through target-responsive hydrogel permeability alteration for sensitive visual quantitative detection

DNA hydrogels have received considerable attention in analytical science, however, some limitations still exist in the applications of intelligent hydrogels. In this paper, we describe a way to prepare gel film in a capillary tube based on the thermal reversible principle of DNA hydrogel and the principle of capillary action. Because of the slight change in the internal structure of gel, its permeability can be increased by the addition of some specific targets. The capillary behavior is thus changed due to the different permeability of the hydrogel film. The duration time of the target solution flowing through the capillary tube with a specified length is used to quantify this change. With this proposed method, ultra-trace DNA hydrogel (0.01 μL) is sufficient to realize the sensitive detection of cocaine without the aid of other instruments, which has a low detection limit (1.17 nM) and good selectivity.

DNA hydrogels have received considerable attention in analytical science but limitations still exist in the applications of intelligent hydrogels. Here, the authors describe a DNA hydrogel sensor for quantitative detection of cocaine based on the permeability change in a DNA hydrogel film.

Target-responsive DNA hydrogel for non-enzymatic and visual detection of glucose

We have successfully developed a target-responsive aptamer cross-linked hydrogel for the visual detection of glucose, an important biomedical analyte. In this work, the glucose-responsive hydrogel was prepared using the target aptamer and its two short complementary DNA strands grafted onto a linear polyacrylamide chain as cross-linkers. Gold nanoparticles (AuNPs) modified with thiol-PEG were encapsulated in the gel and used as the output signal for visible detection. The complex of glucose and its ligand of boronic acid derivatives (Shinkai's receptor) can bind with the aptamer to disrupt the hydrogel, leading to the release of AuNPs with a distinct red colour in the supernatant. By this method glucose can be detected with the naked eye, and the sensor has a detection limit of 0.44 mM in buffer with the help of UV-Vis spectrophotometry. Furthermore, glucose spiked in 50% urine and 30% serum could also be detected respectively with the naked eye, and glucose was quantitatively detected in 50% urine. The hydrogel system provides a non-enzymatic and visual method for glucose detection, and offers promising applications in biotechnology and biomedicine.

A novel ratiometric SERS biosensor with one Raman probe for ultrasensitive microRNA detection based on DNA hydrogel amplification

A ratiometric SERS biosensor with DNA hydrogel-captured glucose oxidase amplification method was fabricated to detect microRNA 122.

How to Construct DNA Hydrogels for Environmental Applications: Advanced Water Treatment and Environmental Analysis

With high binding affinity, porous structures, safety, green, programmability, etc., DNA hydrogels have gained increasing recognition in the environmental field, i.e., advanced treatment technology of water and analysis of specific pollutants. DNA hydrogels have been demonstrated as versatile potential adsorbents, immobilization carriers of bioactive molecules, catalysts, sensors, etc. Moreover, altering components or choosing appropriate functional DNA optimizes environment-oriented hydrogels. However, the lack of comprehensive information hinders the continued optimization. The principle used to fabricate the most suitable hydrogels in terms of the requirements is the focus of this Review. First, different fabrication strategies are introduced and the ideal characteristic for environmental applications is in focus. Subsequently, recent environmental applications and the development of diverse DNA hydrogels regarding their synthesis mechanism are summarized. Finally, the Review provides an insight into the remaining challenging and future perspectives in environmental applications.

30 s Response Time of K+ Ion-Selective Hydrogels Functionalized with 18-Crown-6 Ether Based on QCM Sensor

Potassium detection is critical in monitoring imbalances in electrolytes and physiological status. The development of rapid and robust potassium sensors is desirable in clinical chemistry and point-of-care applications. In this study, composite supramolecular hydrogels are investigated: polyethylene glycol methacrylate and acrylamide copolymer (P(PEGMA-co-AM)) are functionalized with 18-crown-6 ether by employing surface initiated polymerization. Real-time potassium ion monitoring is realized by combining these compounds with quartz crystal microbalance. The device demonstrates a rapid response time of ≈30 s and a concentration detection range from 0.5 to 7.0 × 10^-3 m. These hydrogels also exhibit high reusability and K⁺ ion selectivity relative to other cations in biofluids such as Na⁺ , NH₄⁺ , Mg²⁺ , and Ca²⁺ . These results provide a new approach for sensing alkali metal ions using P(PEGMA-co-AM) hydrogels.

Tuning phase and aging of DNA hydrogels through molecular design

The programmable, sequence-dependent hybridization of DNA has spurred the development of DNA hydrogels, polymer networks that swell in water and are comprised either entirely or partially of DNA. Specific applications require hydrogels of particular structure for optimal functionality. Here, we use self-assembling, multi-valent DNA nanostars to examine how hydrogel structure is influenced by the non-equilibrium dynamics of its interacting components. We show that hydrogel aging kinetics - from an arrested, solid-like percolated network to an equilibrium, phase-separated liquid analogous to coacervates - are modulated by DNA hybridization strength and ion-specific nanostar internal flexibility. Together, our results demonstrate strategies to control hydrogel kinetic phenomena, and thus the hydrogel structure, through the rational design of gel-forming elements and solvent conditions.

Detection of aflatoxin B1 in food samples based on target-responsive aptamer-cross-linked hydrogel using a handheld pH meter as readout

Aflatoxin B₁ (AFB₁) can cause great threat to human health, so the development of convenient and portable device for sensitive detection of AFB₁ is highly desired. The portable pH meter has the characters of facile operation, low cost, and easy availability. Therefore, in this study, we investigate the applicability of utilizing a pH meter as the readout to develop a portable sensor for AFB₁. The specific detection of AFB₁ is realized via the combination of AFB₁-responsive aptamer-cross-linked hydrogel. Upon the addition of AFB₁, AFB₁ binds to its aptamer with high affinity in lieu of aptamer/DNA complex, causing the collapse of hydrogel network and results in the releasing of urease into the solution. The released urease can catalyse the hydrolysis of urea and result in the rise of pH value. The change of pH value has a direct relationship to the concentration of AFB₁ in the range of 0.2-20µM with a detection limit of 0.1µM (S/N = 3). The proposed portable device is successfully applied to assay AFB₁ in the food samples with satisfied results.

Nanotechnology-Enhanced No-Wash Biosensors for in Vitro Diagnostics of Cancer

In vitro biosensors have been an integral component for early diagnosis of cancer in the clinic. Among them, no-wash biosensors, which only depend on the simple mixing of the signal generating probes and the sample solution without additional washing and separation steps, have been found to be particularly attractive. The outstanding advantages of facile, convenient, and rapid response of no-wash biosensors are especially suitable for point-of-care testing (POCT). One fast-growing field of no-wash biosensor design involves the usage of nanomaterials as signal amplification carriers or direct signal generating elements. The analytical capacity of no-wash biosensors with respect to sensitivity or limit of detection, specificity, stability, and multiplexing detection capacity is largely improved because of their large surface area, excellent optical, electrical, catalytic, and magnetic properties. This review provides a comprehensive overview of various nanomaterial-enhanced no-wash biosensing technologies and focuses on the analysis of the underlying mechanism of these technologies applied for the early detection of cancer biomarkers ranging from small molecules to proteins, and even whole cancerous cells. Representative examples are selected to demonstrate the proof-of-concept with promising applications for in vitro diagnostics of cancer. Finally, a brief discussion of common unresolved issues and a perspective outlook on the field are provided.

Carbon-dot–hydrogel for enzyme-mediated bacterial detection

A hybrid carbon-dot (C-dot)–hydrogel matrix was constructed and employed for detection of bacteria.

Recent Progress in Aptamer-Based Functional Probes for Bioanalysis and Biomedicine

Nucleic acid aptamers are short synthetic DNA or RNA sequences that can bind to a wide range of targets with high affinity and specificity. In recent years, aptamers have attracted increasing research interest due to their unique features of high binding affinity and specificity, small size, excellent chemical stability, easy chemical synthesis, facile modification, and minimal immunogenicity. These properties make aptamers ideal recognition ligands for bioanalysis, disease diagnosis, and cancer therapy. This review highlights the recent progress in aptamer selection and the latest applications of aptamer-based functional probes in the fields of bioanalysis and biomedicine.

3D hydrogel scaffold doped with 2D graphene materials for biosensors and bioelectronics

Hydrogels consisting of three-dimensional (3D) polymeric networks have found a wide range of applications in biotechnology due to their large water capacity, high biocompatibility, and facile functional versatility. The hydrogels with stimulus-responsive swelling properties have been particularly instrumental to realizing signal transduction in biosensors and bioelectronics. Graphenes are two-dimensional (2D) nanomaterials with unprecedented physical, optical, and electronic properties and have also found many applications in biosensors and bioelectronics. These two classes of materials present complementary strengths and limitations which, when effectively coupled, can result in significant synergism in their electrical, mechanical, and biocompatible properties. This report reviews recent advances made with hydrogel and graphene materials for the development of high-performance bioelectronics devices. The report focuses on the interesting intersection of these materials wherein 2D graphenes are hybridized with 3D hydrogels to develop the next generation biosensors and bioelectronics.

A target responsive aptamer machine for label-free and sensitive non-enzymatic recycling amplification detection of ATP

Based on a new target-triggered aptamer molecular machine, a label-free and non-enzymatic target recycling amplification strategy for sensitive fluorescence detection of ATP in human serums is described. The presence of the target ATP together with the DNA fuel strand initiates the operation of the aptamer machine and leads to cyclic reuse of ATP and the release of many G-quadruplex sequences, which associate with a fluorescent dye to generate significantly amplified fluorescence signals to achieve sensitive detection of ATP.

Isothermal Amplification of Nucleic Acids

Isothermal amplification of nucleic acids is a simple process that rapidly and efficiently accumulates nucleic acid sequences at constant temperature. Since the early 1990s, various isothermal amplification techniques have been developed as alternatives to polymerase chain reaction (PCR). These isothermal amplification methods have been used for biosensing targets such as DNA, RNA, cells, proteins, small molecules, and ions. The applications of these techniques for in situ or intracellular bioimaging and sequencing have been amply demonstrated. Amplicons produced by isothermal amplification methods have also been utilized to construct versatile nucleic acid nanomaterials for promising applications in biomedicine, bioimaging, and biosensing. The integration of isothermal amplification into microsystems or portable devices improves nucleic acid-based on-site assays and confers high sensitivity. Single-cell and single-molecule analyses have also been implemented based on integrated microfluidic systems. In this review, we provide a comprehensive overview of the isothermal amplification of nucleic acids encompassing work published in the past two decades. First, different isothermal amplification techniques are classified into three types based on reaction kinetics. Then, we summarize the applications of isothermal amplification in bioanalysis, diagnostics, nanotechnology, materials science, and device integration. Finally, several challenges and perspectives in the field are discussed.

Adenosine Triphosphate-Triggered Release of Macromolecular and Nanoparticle Loads from Aptamer/DNA-Cross-Linked Microcapsules

The synthesis of stimuli-responsive DNA microcapsules acting as carriers for different payloads, and being dissociated through the formation of aptamer-ligand complexes is described. Specifically, stimuli-responsive anti-adenosine triphosphate (ATP) aptamer-cross-linked DNA-stabilized microcapsules loaded with tetramethylrhodamine-modified dextran (TMR-D), CdSe/ZnS quantum dots (QDs), or microperoxidase-11 (MP-11) are presented. In the presence of ATP as trigger, the microcapsules are dissociated through the formation of aptamer-ATP complexes, resulting in the release of the respective loads. Selective unlocking of the capsules is demonstrated, and CTP, GTP, or TTP do not unlock the pores. The ATP-triggered release of MP-11 from the microcapsules enables the MP-11-catalyzed oxidation of Amplex UltraRed by H2O2 to the fluorescent product resorufin.

Aptamer-functionalized hydrogel as effective anti-cancer drugs delivery agents

An aptamer-functionalized hydrogel has been developed, which can be regulated by the AS1411 aptamer with the sol-gel conversion. Also the hydrogel can be further utilized for the controlled encapsulation and release of the cancer drugs. Specially, the AS1411 initiates the hybridization of acrydite-modified oligonucleotides to form the hydrogels and the presence of the target protein nucleolin leads the gel to dissolve as a result of reducing the cross-linking density by competitive target-aptamer binding. Based on the rheology of hydrogels, it is possible to utilize this material for storing and releasing molecules. In this research, the cancer drug doxorubicin is encapsulated inside the gel during the formation of the hydrogel and then released in the presence of nucleolin. Further experiments are carried out to prove the specific recognition of target matter. In vitro researches confirm that the aptamer-functionalized hydrogels can be used as drug carriers in targeted therapy and other biotechnological applications.

Au@Pt nanoparticle encapsulated target-responsive hydrogel with volumetric bar-chart chip readout for quantitative point-of-care testing

Point-of-care testing (POCT) with the advantages of speed, simplicity, portability, and low cost is critical for the measurement of analytes in a variety of environments where access to laboratory infrastructure is lacking. While qualitative POCTs are widely available, quantitative POCTs present significant challenges. Here we describe a novel method that integrates an Au core/Pt shell nanoparticle (Au@PtNP) encapsulated target-responsive hydrogel with a volumetric bar-chart chip (V-Chip) for quantitative POCT. Upon target introduction, the hydrogel immediately dissolves and releases Au@PtNPs, which can efficiently catalyze the decomposition of H2 O2 to generate a large volume of O2 to move of an ink bar in the V-Chip. The concentration of the target introduced can be visually quantified by reading the traveling distance of the ink bar. This method has the potential to be used for portable and quantitative detection of a wide range of targets without any external instrument.

Exonuclease I aided enzyme-linked aptamer assay for small-molecule detection

A novel enzyme-linked aptamer assay (ELAA) with the aid of Exonuclease I (Exo I) for colorimetric detection of small molecules was developed. The fluorescein isothiocyanate (FITC)-labeled aptamer was integrated into a double-stranded DNA (dsDNA). In the presence of target, the binding of aptamer with target protected the aptamer from Exo I degradation, which resulted in the FITC tag remaining on the aptamer. Then, the anti-FITC-HRP conjugate was used to produce an optically observable signal. By monitoring the color change, we were able to detect two model molecules, ATP and L-argininamide, with high selectivity and high sensitivity even in the serum matrix. It is expected to be a simple and general ELAA method with wide applicability.

A ratiometric fluorescent hydrogel sensor for zinc(ii) based on a two fluorophore approach

A hydrogel sensor has been developed to measure the concentration of Zn(ii) upon swelling in aqueous buffer.

Fluorescent DNA hydrogels composed of nucleic acid-stabilized silver nanoclusters

Y-shaped DNA units functionalized with Ag-nanoclusters are crosslinked by nucleic acids to yield fluorescent hydrogels with controlled luminescence properties.

Quality control certification of RNA aptamer-based detection

Aptamers are single-stranded DNA or RNA molecules with a defined tertiary structure for molecular recognition. Numerous RNA aptamers with excellent binding affinity and specificity have been reported; they constitute an attractive reservoir of molecular recognition elements for biosensor development. However, RNA is relatively unstable owing to spontaneous hydrolysis and nuclease degradation. Thus, RNA aptamer-based biosensors are prone to producing false-positive signals. Here, we present an RNA aptamer biosensor design strategy that utilises an internal control to distinguish target binding from false-positive signals. The sequence of a chosen RNA aptamer is expanded so that it can form three consecutive short RNA-DNA duplexes with 1) a quencher-labelled DNA strand (Q(1)DNA), 2) a dual-fluorophore-labelled DNA strand (F(1)DNAF(2)) and 3) another quencher-labelled DNA strand (Q(2)DNA). The addition of a target releases Q(2)DNA from the duplex assembly, and produces the expected positive signal from F(2). However, the authenticity of target recognition is validated only if no signal is generated from F(1). We have successfully engineered two fluorescent reporters by using an RNA aptamer that binds thrombin and one that binds theophylline. Both reporters show the expected binding affinity and specificity, and are capable of reporting system malfunction when treated with nucleases and chemical denaturants. This strategy provides a simple and reliable way to ensure high-quality detection when RNA aptamers are employed as molecular-recognition elements.

Self-Assembly for the Synthesis of Functional Biomaterials

The use of self-assembly for the construction of functional biomaterials is a highly promising and exciting area of research, with great potential for the treatment of injury or disease. By using multiple noncovalent interactions, coded into the molecular design of the constituent components, self-assembly allows for the construction of complex, adaptable, and highly tunable materials with potent biological effects. This review describes some of the seminal advances in the use of self-assembly to make novel systems for regenerative medicine and biology. Materials based on peptides, proteins, DNA, or hybrids thereof have found application in the treatment of a wide range of injuries and diseases, and this review outlines the design principles and practical applications of these systems. Most of the examples covered focus on the synthesis of hydrogels for the scaffolding or transplantation of cells, with an emphasis on the biological, mechanical, and structural properties of the resulting materials. In addition, we will discuss the distinct advantages conferred by self-assembly (compared with traditional covalent materials), and present some of the challenges and opportunities for the next generation of self-assembled biomaterials.

Amplified fluorescence aptamer-based sensors using exonuclease III for the regeneration of the analyte

Quick and easy detection: The Exo III-stimulated regeneration of the analyte by the digestion of supramolecular aptamer-analyte complexes provides a means to develop amplified optical aptasensors (see figure).