Ultrasensitive and selective detection of nicotinamide adenine dinucleotide by target-triggered ligation-rolling circle amplification

Design of supramolecular hybrid nanomaterials comprising peptide-based supramolecular nanofibers and in situ generated DNA nanoflowers through rolling circle amplification

The artificial construction of multicomponent supramolecular materials comprising plural supramolecular architectures that are assembled orthogonally from their constituent molecules has attracted growing attention. Here, we describe the design and development of multicomponent supramolecular materials by combining peptide-based self-assembled fibrous nanostructures with globular DNA nanoflowers constructed by the rolling circle amplification reaction. The orthogonally constructed architectures were dissected by fluorescence imaging using the selective fluorescence staining procedures adapted to this study. The present, unique hybrid materials developed by taking advantage of each supramolecular architecture based on their peptide and DNA functions may offer distinct opportunities to explore their bioapplications as a soft matrix.

A trifunctional split dumbbell probe coupled with ligation-triggered isothermal rolling circle amplification for label-free and sensitive detection of nicotinamide adenine dinucleotide

The nicotinamide adenine dinucleotide (NAD⁺) is an important small biomolecule that participates in a variety of physiological functions, and it has been regarded as a potential biomarker for disease diagnosis and a promising target for disease treatment. The conventional methods for NAD⁺ assay often suffer from complicated procedures, expensive labeling, poor selectivity, and unsatisfactory sensitivity. Herein, we develop a label-free and sensitive method for NAD⁺ assay based on the integration of a trifunctional split dumbbell probe with ligation-triggered isothermal rolling circle amplification (RCA). We design a trifunctional split dumbbell probe that can act as a probe for NAD⁺ recognition, a template for RCA reaction, and a substrate for SYBR Green I binding. In the presence of target NAD⁺, it can serve as a cofactor to active E. coli DNA ligase which subsequently catalyzes the ligation of split dumbbell probe to form a circular template for RCA reaction, generating numerous dumbbell probe amplicons which can be easily and label-free monitored by using SYBR Green I as the fluorescent indicator. Due to the high fidelity of NAD⁺-dependent ligation and high amplification efficiency of RCA amplification, this method exhibits high sensitivity with a detection limit of 85.6 fM and good selectivity with the capability of discriminating target NAD⁺ from its analogs. Moreover, this method can be applied for accurate and sensitive detection of NAD⁺ in complex biological samples and cancer cells, holding great potential in NAD⁺-related biological researches and clinical diagnosis.

A rapidly self-assembling soft-brush DNA hydrogel based on RCA products

A rapid self-assembly strategy was developed for fabricating a novel soft-brush DNA hydrogel in one minute by introducing a pair of L-type probes into the RCA products. The L-type probes with universality achieved a controllable size and morphology of the DNA hydrogel, providing deeper insight into variability and probability in functional biomaterials.

Rational construction of a DNA nanomachine for HIV nucleic acid ultrasensitive sensing

HIV nucleic acids, one kind of significant biomarker, play an important role in fundamental studies and clinical diagnosis. Importantly, the early accurate diagnosis for HIV nucleic acids at ultralow concentrations can potentially extend the life of patients. In the current work, we developed a DNA nanomachine on gold nanoparticles (AuNPs) coupling rolling circle amplification and DNA walker cascade amplification for ultrasensitive detection of HIV nucleic acids. This DNA nanomachine sensing strategy exhibits a significantly low detection limit down to 1.46 fM. Furthermore, this DNA nanomachine biosensor is capable of detecting target DNA in real samples because of its high selectivity and sensitivity. Moreover, the DNA nanomachine biosensor is capable of discriminating single-base mismatch lower than 3.5 pM. The results showed that this DNA nanomachine biosensor has the potential for biomedical studies and clinical applications.

Highly Stable Mesoporous Luminescence-Functionalized MOF with Excellent Electrochemiluminescence Property for Ultrasensitive Immunosensor Construction

In this work, a novel mesoporous luminescence-functionalized metal-organic framework (Ru-PCN-777) with high stability and excellent electrochemiluminescence (ECL) performance was synthesized by immobilizing Ru(bpy)₂(mcpbpy)²⁺ on the Zr₆ cluster of PCN-777 via a strong coordination bond between Zr⁴⁺ and -COO^-. Consequently, the Ru(bpy)₂(mcpbpy)²⁺ could not only cover the surface of PCN-777 but also graft into the interior of PCN-777, which greatly increased the loading amount of Ru(bpy)₂(mcpbpy)²⁺ and effectively prevented the leaching of the Ru(bpy)₂(mcpbpy)²⁺ resulting in a stable and high ECL response. Considering the above merits, we utilized the mesoporous Ru-PCN-777 to construct an ECL immunosensor to detect mucin 1 (MUC1) based on proximity-induced intramolecular DNA strand displacement (PiDSD). The ECL signal was further enhanced by the enzyme-assisted DNA recycling amplification strategy. As expected, the immunosensor had excellent sensitivity, specificity, and responded wide linearly to the concentration of MUC1 from 100 fg/mL to 100 ng/mL with a low detection limit of 33.3 fg/mL (S/N = 3). It is the first time that mesoporous Zr-MOF was introduced into ECL system to assay biomolecules, which might expand the application of mesoporous metal-organic frameworks (MOFs) in bioanalysis. This work indicates that the use of highly stable mesoporous luminescence-functionalized MOFs to enhance the ECL intensity and stability is a feasible strategy for designing and constructing high-performance ECL materials, and therefore may shed light on new ways to develop highly sensitive and selective ECL sensors.

A pure DNA hydrogel with stable catalytic ability produced by one-step rolling circle amplification

A rolling-circle-amplification method was developed to produce DNA hydrogels with horseradish-peroxidase-like catalytic capability. The catalytic hydrogel exhibits highly improved stability at elevated temperatures or during a long-term storage. Integrated with glucose oxidase, the complex hydrogel can be applied to the sensitive and reliable detection of glucose.

An ultrasensitive electrochemical biosensor for the detection of mecA gene in methicillin-resistant Staphylococcus aureus

Electrochemical DNA biosensor has unique advantages for on-site pathogenic microorganism detection, yet the detection of long DNA towards genome DNA (gDNA) analysis remains challenge. In this work, we report a novel electrochemical biosensor for the ultrasensitive analysis of mecA DNA on methicillin-resistant Staphylococcus aureus (MRSA) genome, using a multi-signal probes (MSP) system. The MSP consists of 7 biotin-labelled signal probes that will combine to the target DNA in a prehybridization step, and then the complex will be captured by a DNA tetrahedron structure probe (TSP) on the electrode surface. Then, after the introduction of the streptavidin-labelled HRP enzyme, a catalysis current signal is detected that is found to be corresponding to the concentration of the target DNA. MSP in this work plays a critical role not only for the signal amplification through bringing 7 biotins, but also dramatically improves the accessibility of the target sequence embedded in the double-strand DNA molecules and complex second structures. The 3-D DNA TSP here provides steady support and optimized surface density for the very "large" complex of MSP system and gDNA, as a base of the capture probe. Finally, as low as 10fM synthetic target DNA was successfully detected, which is at least 3 magnitudes lower than that using single signal probe. Most importantly, we demonstrated the practicability of our analysis method by analyzing a 57fM MRSA gDNA sample showing excellent selectivity, and the reliability of the analysis was also demonstrated by digital PCR.

Nicotinamide adenine dinucleotide detection based on silver nanoclusters stabilized by a dumbbell-shaped probe

We have developed a novel method for detecting nicotinamide adenine dinucleotide (NAD⁺) based on fluorescent silver nanoclusters (AgNCs) stabilized by a dumbbell-shaped DNA template containing two cytosine-loops joined in a dsDNA stem. The design involves two types of components: a dumbbell-shaped DNA template and three enzymes. In the presence of NAD⁺ as a cofactor, Escherichia coli DNA ligase (E.coli DNA ligase) catalyzes template ligation to generate a sealed (no terminal nucleotides) dumbbell-shaped structure, preventing digestion by exonuclease III (Exo III) and exonuclease I (Exo I). The loop regions of the intact template serve as sites for the deposition of highly fluorescent AgNCs. In the absence of NAD⁺, the ligation reaction does not occur, and the unsealed dumbbell-shaped template is digested into mononucleotides via cooperation of Exo III and Exo I. The destruction of the DNA template results in the agglomeration of AgNCs into silver nanoparticles with low fluorescence. The fluorescence enhancement depends on the ligation and digestion of the DNA template, allowing quantitative detection of NAD⁺ in the range of 0.5 nM-5000 nM with a detection limit of ∼0.25 nM.

Hairpin stabilized fluorescent silver nanoclusters for quantitative detection of NAD+ and monitoring NAD+/NADH based enzymatic reactions

A set of 90 mer long ssDNA candidates, with different degrees of cytosine (C-levels) (% and clusters) was analyzed for their function as suitable Ag-nanocluster (AgNC) nucleation scaffolds. The sequence (P4) with highest C-level (42.2%) emerged as the only candidate supporting the nucleation process as evident from its intense fluorescence peak at λ_{660 nm}. Shorter DNA subsets derived from P4 with only stable hairpin structures could support the AgNC formation. The secondary hairpin structures were confirmed by PAGE, and CD studies. The number of base pairs in the stem region also contributes to the stability of the hairpins. A shorter 29 mer sequence (Sub 3) (ΔG = -1.3 kcal/mol) with 3-bp in the stem of a 7-mer loop conferred highly stable AgNC. NAD⁺ strongly quenched the fluorescence of Sub 3-AgNC in a concentration dependent manner. Time resolved photoluminescence studies revealed the quenching involves a combined static and dynamic interaction where the binding constant and number of binding sites for NAD⁺ were 0.201 L mol^-1 and 3.6, respectively. A dynamic NAD⁺ detection range of 50-500 μM with a limit of detection of 22.3 μM was discerned. The NAD⁺ mediated quenching of AgNC was not interfered by NADH, NADP⁺, monovalent and divalent ions, or serum samples. The method was also used to follow alcohol dehydrogenase and lactate dehydrogenase catalyzed physiological reactions in a turn-on and turn-off assay, respectively. The proposed method with ssDNA-AgNC could therefore be extended to monitor other NAD⁺/NADH based enzyme catalyzed reactions in a turn-on/turn-off approach.

Synthesis and sensing integration: A novel enzymatic reaction modulated Nanoclusters Beacon (NCB) "Illumination" strategy for label-free biosensing and logic gate operation

A novel fluorescent label-free "turn-on" NAD(+) and adenosine triphosphate (ATP) biosensing strategy is proposed by fully exploiting ligation triggered Nanocluster Beacon (NCB). In the presence of the target, the split NCB was brought to intact, which brought the C-rich sequence and enhancer sequence in close proximity resulting in the lightening of dark DNA/AgNCs ("On" mode). Further application was presented for logic gate operation and aptasensor construction. The feasibility was investigated by Ultraviolet-visible spectroscopy (UV-vis), Fluorescence, lifetime and High Resolution Transmission Electron Microscopy (HRTEM) etc. The strategy displayed good performance in the detection of NAD(+) and ATP, with the detection limit of 0.002nM and 0.001mM, the linear range of 10-1000nM and 0.003-0.01mM, respectively. Due to the DNA/AgNCs as fluorescence reporter, the completely label-free fluorescent strategy boasts the features of simplicity and low cost, and showing little reliance on the sensing environment. Meanwhile, the regulation by overhang G-rich sequence not relying on Förster energy transfer quenching manifests the high signal-to-background ratios (S/B ratios). This method not only provided a simple, economical and reliable fluorescent NAD(+) assay but also explored a flexible G-rich sequence regulated NCB probe for the fluorescent biosensors. Furthermore, this sensing mode was expanded to the application of a logic gate design, which exhibited a high performance for not only versatile biosensors construction but also for molecular computing application.

Zero-Background Helicase-Dependent Amplification and Its Application to Reliable Assay of Telomerase Activity in Cancer Cell by Eliminating Primer-Dimer Artifacts

Primer-dimer artifacts resulting from unintended template-independent primer-primer interactions often hinder the specific amplification of nucleic acids. We demonstrate, for the first time, zero-background helicase-dependent amplification (HDA), with low concentrations of both ATP and dNTPs. This strategy achieved the reliable evaluation of telomerase activity in cancer cells by eliminating primer-dimer artifacts, which have plagued many previous methods with reduced specificity. We found that the performance of the telomerase assay by zero-background HDA was negatively affected by highly concentrated cellular proteins. This inhibitory effect is attributed to the binding of DNA templates to proteins, thus making them unavailable for polymerases. However, gold nanoparticles were demonstrated to highly attenuate such inhibition by abundant proteins, and to enhance the assay sensitivity and reliability when the reaction was performed with concentrated cell extracts.

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.

A label-free fluorescence strategy for selective detection of nicotinamide adenine dinucleotide based on a dumbbell-like probe with low background noise

In this work we developed a novel label-free fluorescence sensing approach for the detection of nicotinamide adenine dinucleotide (NAD(+)) based on a dumbbell-like DNA probe designed for both ligation reaction and digestion reaction with low background noise. SYBR Green I (SG I), a double-helix dye, was chosen as the readout fluorescence signal. In the absence of NAD(+), the ligation reaction did not occur, but the probe was digested to mononucleotides after the addition of exonuclease I (Exo I) and exonuclease I (Exo III), resulting in a weak fluorescence intensity due to the weak interaction between SG I and mononucleotides. In the presence of NAD(+), the DNA probe was ligated by Escherichia coli DNA ligase, blocking the digestion by Exo I and Exo III. As a result, SG I was intercalated into the stem part of the DNA dumbbell probe and fluorescence enhancement was achieved. This method was simple in design, fast to operate, with good sensitivity and selectivity which could discriminate NAD(+) from its analogs.

A novel strategy to analyze L-tryptophan through allosteric Trp repressor based on rolling circle amplification

Rolling circle amplification (RCA) has been considered as a powerful tool for nucleic acids detection. Here, a novel repressor-RCA-based method for L-tryptophan (L-Trp) detection was developed. This method utilizes the specific interaction between the RCA circular template and the Trp repressor protein (TrpR) involved in trp operon of Escherichia coli (E. coli). In the absence of L-Trp, the TrpR protein could not bind to the RCA template, and the RCA process can be continued. When L-Trp is present, the activated TrpR will bind to the operon sequence on the RCA template and inhibit the RCA reaction. Thus, the concentration of L-Trp is correlated directly with the fluorescent RCA signals. We succeeded in detecting L-Trp in a single step in simple homogeneous reaction system. The detection limit was estimated to be 0.77 μM (S/N=3) with good linearity. The method can unambiguously distinguish L-Trp from other 19 standard amino acids and L-Trp analogs. This strategy is also promising for detecting many small molecules such as other amino acids and carbohydrates.

A linear DNA probe as an alternative to a molecular beacon for improving the sensitivity of a homogenous fluorescence biosensing platform for DNA detection using target-primed rolling circle amplification

Linear single-labeled DNA probes are used in this RCA-based fluorescence strategy for DNA detection, which could effectively avoid the fluorescence quenching between neighboring signal probes using hairpin probe as signal probe.

Ligation-triggered fluorescent silver nanoclusters system for the detection of nicotinamide adenine dinucleotide

Herein, we demonstrate a novel silver nanocluster-based fluorescent system for the detection of nicotinamide adenine dinucleotide (NAD(+)), an important biological small molecule involved in a wide range of biological processes. A single-stranded dumbbell DNA probe was designed and used for the assay, which contained a nick in the stem, a poly-cytosine nucleotide loop close to 5' end as the template for the formation of highly fluorescent silver nanoclusters (Ag NCs) and another loop close to 3' end. Only in the presence of NAD(+), the probe was linked at 5' and 3' ends by Escherichia coli DNA ligase, which blocked the DNA polymerase-based extension reaction, ensuring the formation of fluorescent Ag NCs. This technique provided a logarithmic linear relationship in the range of 1 pM-500 nM with a detection limit of as low as 1 pM NAD(+), and exhibited high selectivity against its analogues, and was then successfully used for the detection of NAD(+) level in four kinds of cell homogenates. In addition, this new approach was conducted in an isothermal and homogeneous condition without the need of any thermal cycling, washing, and separation steps, making it very simple. Overall, this label-free protocol offers a promising alternative for the detection of NAD(+), taking advantage of specificity, sensitivity, cost-efficiency, and simplicity.

Target-responsive dumbbell probe-mediated rolling circle amplification strategy for highly sensitive Hg2+ detection

A novel label-free amplified fluorescent sensing scheme based on target-responsive dumbbell probe-mediated rolling circle amplification (D-RCA) has been developed for sensitive and selective detection of mercuric ions.

A novel label-free cascade amplification strategy based on dumbbell probe-mediated rolling circle amplification-responsive G-quadruplex formation for highly sensitive and selective detection of NAD+ or ATP

A novel label-free fluorescent sensing scheme for sensitive and selective detection of NAD(+) and ATP has been developed based on dumbbell probe-mediated rolling circle amplification (D-RCA)-responsive G-quadruplex formation. This approach can detect 0.5 pM for ATP and 100 fM for NAD(+), much lower than those of previously reported biosensors, and exhibits high discrimination ability.

Inhibition of G-quadruplex assembling by DNA ligation: a versatile and non-covalent labeling strategy for bioanalysis

Through tuning relative thermodynamic stabilities (I, II and III), DNA ligation was coupled to split G-quadruplex probes and a versatile, non-covalent labelling and fluorescent strategy was constructed based on inhibition of template-directed G-quadruplex assembling by ligation reaction. The non-covalent complex between G-quadruplex and fluorescent probe was employed as signalling label and thus covalent modification of DNA probes with fluorescent probes was avoided. Selective detection of small biomolecules (ATP and NAD(+)) in the nanomolar range was realized due to the cofactor-dependent activity of DNA ligases (T4 and Escherichia coli DNA ligase). By virtue of the simple strategy, the effect of mismatch position of single-base mismatched template DNA on the ligation efficiency was validated. Meanwhile, highly mismatch-influenced ligation efficiency of ligase endows the cost-effective strategy great potential for single-nucleotide polymorphism (SNP) analysis. The non-covalent labeling strategy provides a versatile and cost-effective platform for monitor of DNA ligation, cofactor detection, SNP analysis and other ligase-based assays.

3-Hydroxybutyrate methyl ester as a potential drug against Alzheimer's disease via mitochondria protection mechanism

Alzheimer's disease (AD) is induced by many reasons, including decreased cellular utilization of glucose and brain cell mitochondrial damages. Degradation product of microbially synthesized polyhydroxybutyrate (PHB), namely, 3-hydroxybutyrate (3HB), can be an alternative to glucose during sustained hypoglycemia. In this study, the derivative of 3HB, 3-hydroxybutyrate methyl ester (HBME), was used by cells as an alternative to glucose. HBME inhibited cell apoptosis under glucose deprivation, rescued activities of mitochondrial respiratory chain complexes that were impaired in AD patients and decreased the generation of ROS. Meanwhile, HBME stabilized the mitochondrial membrane potential. In vivo studies showed that HBME crossed the blood brain barrier easier compared with charged 3HB, resulting in a better bioavailability. AD mice treated with HBME performed significantly better (p < 0.05) in the Morris water maze compared with other groups, demonstrating that HBME has a positive in vivo pharmaceutical effect to improve the spatial learning and working memory of mice. A reduced amyloid-β deposition in mouse brains after intragastric administration of HBME was also observed. Combined with the in vitro and in vivo results, HBME was proposed to be a drug candidate against AD, its working mechanism appeared to be mediated by various effects of protecting mitochondrial damages.

Additional molecular biological amplification strategy for enhanced sensitivity of monitoring low-abundance protein with dual nanotags

A new signal-on immunoassay protocol for sensitive electronic detection of alpha-fetoprotein (AFP) was developed by coupling with metal sulfide nanolabels and a silver nanocluster (AgNC)-based rolling circle amplification (RCA) strategy. Initially, a sandwiched immunocomplex was formed on a primary antibody-coated microplate using a PbS nanoparticle-labeled polyclonal anti-AFP antibody (PbS-pAb2) as the detection antibody, and then the carried PbS-pAb2 was dissolved by acid to release a large number of lead ions, which could induce the cleavage of lead-specific DNAzyme immobilized on the electrode. The residual single-stranded DNA on the electrode could be used as the primer to produce numerous repeated oligonucleotide sequences via the RCA reaction for the hybridization with many AgNC-labeled detection probes, resulting in the amplification of the electronic signal due to the unique properties of silver nanoclusters. Under optimal conditions, the developed immunoassay exhibited high sensitivity for the detection of AFP with a dynamic range of 0.001-200 ng mL(-1) and a detection limit (LOD) of 0.8 pg mL(-1). Intra-assay and interassay coefficients of variation were below 8.0% and 10%, respectively. Importantly, the methodology was evaluated by analyzing 12 clinical serum specimens, and no significant differences were encountered in comparison with the conventional enzyme-linked immunosorbent assay (ELISA) method.

Few-layer graphene sheets with embedded gold nanoparticles for electrochemical analysis of adenine

This work describes the synthesis of few-layer graphene sheets embedded with various amounts of gold nanoparticles (Gr-Au-x) over an Au_x/MgO catalytic system (where × = 1, 2, or 3 wt%). The sheet-like morphology of the Gr-Au-x nanostructures was confirmed by transmission electron microscopy and high resolution transmission electron microscopy, which also demonstrated that the number of layers within the sheets varied from two to seven. The sample with the highest percentage of gold nanoparticles embedded within the graphitic layers (Gr-Au-3) showed the highest degree of crystallinity. This distinct feature, along with the large number of edge-planes seen in high resolution transmission electron microscopic images, has a crucial effect on the electrocatalytic properties of this material. The reaction yields (40%–50%) and the final purity (96%–98%) of the Gr-Au-x composites were obtained by thermogravimetric analysis. The Gr-Au-x composites were used to modify platinum substrates and subsequently to detect adenine, one of the DNA bases. For the bare electrode, no oxidation signal was recorded. In contrast, all of the modified electrodes showed a strong electrocatalytic effect, and a clear peak for adenine oxidation was recorded at approximately +1.05 V. The highest increase in the electrochemical signal was obtained using a platinum/Gr-Au-3-modified electrode. In addition, this modified electrode had an exchange current density (I₀, obtained from the Tafel plot) one order of magnitude higher than that of the bare platinum electrode, which also confirmed that the transfer of electrons took place more readily at the Gr-Au-3-modified electrode.

One-step highly sensitive florescence detection of T4 polynucleotide kinase activity and biological small molecules by ligation-nicking coupled reaction-mediated signal amplification

DNA phosphorylation, catalyzed by polynucleotide kinase (PNK), plays significant regulatory roles in many biological events. Herein, using T4 PNK as a model target, we describe a one-step, highly sensitive, simple and rapid fluorescence approach for monitoring its activity and inhibition. This innovative strategy is inspired by the great amplification capability of ligation-nicking coupled reaction-mediated signal amplification. In the presence of T4 PNK, one of two short oligonucleotides complementary to the loop sequence of molecular beacon (MB) are phosphorylated, and then ligated with the other by DNA ligase. Upon formation of the stable duplex between the ligated DNA and MB, the fluorescence is restored and further significantly amplified through nicking endonuclease assisted cleavage of multiple MBs. Meanwhile, the cleavage of MBs will also generate new nicks to initiate the ligation reaction. Eventually, a maximum fluorescence enhancement is obtained when the ligation and nicking process reached a dynamic equilibrium. As compared to those of the existing approaches except for the assay based on single nanoparticle counting, all limited to 1:1 signal transduction function, the sensitivity (0.00001U/mL) of the proposed strategy is 100-1700 times higher. The application of the sensing system in complex biological matrix and screening of T4 PNK inhibition are demonstrated with satisfactory results. Moreover, this approach is also successfully used to detect biological small molecules such as adenosine triphosphate (ATP), and can be further extended for nicotinamide adenine dinucleotide (NAD(+)) detection.

A target-activated autocatalytic DNAzyme amplification strategy for the assay of base excision repair enzyme activity

Based on a target-activated autocatalytic DNAzyme amplification strategy, novel fluorescence sensing platforms were constructed for highly sensitive and selective assay of base excision repair enzyme activity. By using a rolling circle amplification (RCA)-coupled amplification cascade, an extremely low detection limit (0.002 U mL(-1)) was achieved.