Toehold-mediated DNA strand displacement-driven super-fast tripedal DNA walker for ultrasensitive and label-free electrochemical detection of ochratoxin A

A label-free ratiometric homogeneous electrochemical aptasensor based on dual catalytic hairpin self-assembly for rapid and sensitive detection of ochratoxin A in food

The food contamination with Ochratoxin A (OTA) has highlighted the need to create precise, sensitive, and convenient techniques. Herein, we proposed a label-free and immobilization-free ratiometric homogeneous electrochemical aptasensor based on dual catalytic hairpin self-assembly (CHA) for OTA detection. Methylene blue (MB) and ferrocene (Fc) in solution were utilized as label-free signaling molecules, generating a response signal (IMB) and a reference signal (IFc), respectively. The ratio of IMB/IFc was utilized as a measure to quantify OTA. Dual CHA was exploited to increase the ratiometric signal and enhance the amplification efficiency. This aptasensor achieved trace-level detection for OTA over a linear range of lower concentrations (1.0 × 10-3 ng/mL-1.0 × 103 ng/mL) with LOD of 92 fg/mL. The aptasensor was successfully applied to detect OTA in cereal and wine, with comparable results of HPLC-MS/MS. This strategy provided a viable platform for rapid, sensitive, and accurate detection of OTA in food.

Efficient DNA walker guided by ordered cruciform-shaped DNA track for ultrasensitive and rapid electrochemical detection of lead ion

The rational design of DNA tracks is an effective pathway to guide the autonomous movement and high-efficiency recognition in DNA walkers, showing outstanding advantages for the cascade signal amplification of electrochemical biosensors. However, the uncontrolled distance between two adjacent tracks on the electrode could increase the risk of derailment and interruption of the reaction. Hence, a novel four-way balanced cruciform-shaped DNA track (C-DNT) was designed as a structured pathway to improve the effectiveness and stability of the reaction in DNA walkers. In this work, two kinds of cruciform-shaped DNA were interconnected as a robust structure that could avoid the invalid movement of the designed DNA walker on the electrode. When hairpin H2 was introduced onto the electrode, the strand displacement reaction (SDR) effectively triggered movements of the DNA walker along the cruciform-shaped track while leaving ferrocene (Fc) on the electrode, leading to a significant enhancement of the electrochemical signal. This design enabled the walker to move in an excellent organized and controllable manner, thus enhancing the reaction speed and walking efficiency. Compared to other walkers moving on random tracks, the reaction time of the C-DNT-based DNA walker could be reduced to 20 min. Lead ion (Pb2+) was used as a model target to evaluate the analytical performance of this biosensor, which exhibited a low detection limit of 0.033 pM along with a wide detection ranging from 0.1 pM to 500 nM. This strategy presented a novel concept for designing a high-performance DNA walker-based sensing platform for the detection of contaminants.

Host-Guest Recognition-Mediated Supramolecular Aggregation-Induced Electrochemiluminescence of Iridium(III) Complexes for Nucleic Acid Bioassay

Currently reported aggregation-induced electroluminescence (AIECL) is usually based on the electrostatic integration of luminous monomers, and its application is still limited by the low ECL efficiency and poor structural stability of electrostatic integration-based AIECL emitters. Herein, host-guest recognition-mediated supramolecular AIECL was creatively developed to overcome the defects of electrostatic-integration-based AIECL. Cucurbit[8]uril (CB[8]) as the host recognized tris (2-phenylpyridine) iridium(III) [Ir(ppy)3] as the guest to form a novel supramolecular complex Ir-CB[8]. CB[8] can not only provide a large hydrophobic cavity to efficiently load Ir(ppy)3 and enrich coreactant tripropylamine but also utilize its carbonyl-laced portals to form intramolecular hydrogen bonds to stabilize the supramolecular structure, so Ir-CB[8] revealed excellent AIECL performance. The AIECL emitter Ir-CB[8] coupled the efficient DNA walker to construct a sensing system for miRNA-16 detection. Au nanoparticles@norepinephrine (AuNPs@NE) trapped by single-strand S1 was developed to significantly quench the ECL emission of Ir-CB[8]. When the target microRNA-16 (miRNA-16) existed, H1 was opened and the sequential assembly from H2 to H7 was triggered, forming "windmill"-like DNA walker with six Pb2+-dependent leg DNA. The assembled DNA walker, which was centered on DNA structure, had high efficiency and biocompatibility and can cut S1 to keep the DNA fragment-carrying quencher AuNPs@NE away from the electrode surface, thus restoring the ECL emission of Ir-CB[8] and realizing ultrasensitive detection of miRNA-16. Supramolecular AIECL mediated by host-guest recognition provides a new way for constructing AIECL emitters with excellent structural stability and AIECL efficiency, and an Ir-CB[8] coupling "windmill"-like DNA walker builds a promising ECL-sensing system for bioassay.

A novel activation function based on DNA enzyme-free hybridization reaction and its implementation on nonlinear molecular learning systems

With the advent of the post-Moore's Law era, the development of traditional silicon-based computers has reached its limit, and there is an urgent need to develop new computing technologies to meet the needs of science, technology, and daily life. Due to its super-strong parallel computing capability and outstanding data storage capacity, DNA computing has become an important branch and hot research topic of new computer technology. DNA enzyme-free hybridization reaction technology is widely used in DNA computing, showing excellent performance in computing power and information processing. Studies have shown that DNA molecules not only have the computing function of electronic devices, but also exhibit certain human brain-like functions. In the field of artificial intelligence, activation functions play an important role as they enable artificial intelligence systems to fit and predict non-linear and complex variable relationships. Due to the difficulty of implementing activation functions in DNA computing, DNA circuits cannot easily achieve all the functions of artificial intelligence. DNA circuits need to rely on electronic computers to complete the training and learning process. Based on the parallel computing characteristics of DNA computing and the kinetic features of DNA molecule displacement reactions, this paper proposes a new activation function. This activation function can not only be easily implemented by DNA enzyme-free hybridization reaction reactions, but also has good nesting properties in DNA circuits, and can be cascaded with other DNA reactions to form a complete DNA circuit. This paper not only provides the mathematical analysis of the proposed activation function, but also provides a detailed analysis of its kinetic features. The activation function is then nested into a nonlinear neural network for DNA computing. This system is capable of fitting and predicting a certain nonlinear function.

Research progress in the detection of common foodborne hazardous substances based on functional nucleic acids biosensors

With the further improvement of food safety requirements, the development of fast, highly sensitive, and portable methods for the determination of foodborne hazardous substances has become a new trend in the food industry. In recent years, biosensors and platforms based on functional nucleic acids, along with a range of signal amplification devices and methods, have been established to enable rapid and sensitive determination of specific substances in samples, opening up a new avenue of analysis and detection. In this paper, functional nucleic acid types including aptamers, deoxyribozymes, and G-quadruplexes which are commonly used in the detection of food source pollutants are introduced. Signal amplification elements include quantum dots, noble metal nanoparticles, magnetic nanoparticles, DNA walkers, and DNA logic gates. Signal amplification technologies including nucleic acid isothermal amplification, hybridization chain reaction, catalytic hairpin assembly, biological barcodes, and microfluidic system are combined with functional nucleic acids sensors and applied to the detection of many foodborne hazardous substances, such as foodborne pathogens, mycotoxins, residual antibiotics, residual pesticides, industrial pollutants, heavy metals, and allergens. Finally, the potential opportunities and broad prospects of functional nucleic acids biosensors in the field of food analysis are discussed.

A micro-nano interface integrated SERS-based microfluidic sensor for miRNA detection using DNAzyme walker amplification

BACKGROUND

Precise and specific miRNA detection plays a vital role in exploring development mechanisms of cancer disease, thereby it can significantly improve relevant prevention and treatment strategies.

RESULTS

In this work, a surface-enhanced Raman spectroscopy (SERS)-based microfluidic chip has been devised with a microcone array SERS substrate (MCASS) for the miR-141 detection. This substrate excels in unique SERS activity and large surface area for DNA oligonucleotide modification. As the presence of miR-141, the DNAzyme walker induced cleavage reaction took place on the finely designed and prepared dual DNA conjugated SERS nanoprobes. The SERS nanoprobes can anchor on MCASS by the DNA hybridization that achieved an impressive detection limit in the femtomolar level.

SIGNIFICANCE

With this integrated SERS-based microfluidic chip, we provided a miRNA detection strategy using DNAzyme walker amplification technology. It is believed that this strategy could be a powerful tool for miRNA detection and related cancer screening test.

Strategy of functional nucleic acids-mediated isothermal amplification for detection of foodborne microbial contaminants: A review

Foodborne microbial contamination (FMC) is the leading cause of food poisoning and foodborne illness. The foodborne microbial detection methods based on isothermal amplification have high sensitivity and short detection time, and functional nucleic acids (FNAs) could extend the detectable object of isothermal amplification to mycotoxins. Therefore, the strategy of FNAs-mediated isothermal amplification has been emergingly applied in biosensors for foodborne microbial contaminants detection, making biosensors more sensitive with lower cost and less dependent on nanomaterials for signal output. Here, the mechanism of six isothermal amplification technologies and their application in detecting FMC is firstly introduced. Then the strategy of FNAs-mediated isothermal amplification is systematically discussed from perspectives of FNAs' versatility including recognition elements (Aptamer, DNAzyme), programming tools (DNA tweezer, DNA walker and CRISPR-Cas) and signal units (G-quadruplex, FNAs-based nanomaterials). Finally, challenges and prospects are presented in terms of addressing the issue of nonspecific amplification reaction, developing better FNAs-based sensing elements and eliminating food matrix effects.

An accurate and ultrasensitive ratiometric electrochemical aptasensor for determination of Ochratoxin A based on catalytic hairpin assembly

Ochratoxin A (OTA) pollution in agricultural products has raised the pressing to develop sensitive, accurate and convenient detection methods. Herein, an accurate and ultrasensitive ratiometric electrochemical aptasensor was proposed based on catalytic hairpin assembly (CHA) for OTA detection. In this strategy, the target recognition and CHA reaction were both accomplished in the same system, which avoided tedious multi-steps operation and extra reagents, providing the advantage of convenience with only a one-step reaction and without enzyme. The labeled Fc and MB were used as the signal-switching molecules, avoiding various interferences and greatly improving the reproducibility (RSD: 3.197%). This aptasensor achieved trace-level detection for OTA with LOD of 81 fg/mL in the linear range of lower concentration (100 fg/mL-50 ng/mL). Moreover, this strategy was successfully applied to OTA detection in cereals with comparable results of HPLC-MS. This aptasensor provided a viable platform for accurate, ultrasensitive, and one-step detection of OTA in food.

A visual detection strategy for SARS-CoV-2 based on dual targets-triggering DNA walker

SARS-CoV-2, a highly transmissible and mutagenic virus, made huge threats to global public health. The detection strategies, which are free from testing site requirements, and the reagents and instruments are portable, are vital for early screening and play a significant role in curbing the spread. This work proposed a silver-coated glass slide (SCGS)/DNA walker based on a dual targets-triggering mechanism, enzyme-catalyzed amplification, and smartphone data analysis, which build a portable visual detection strategy for the SARS-CoV-2 RNA-dependent RNA polymerase (RdRp) gene. By this method, the detection was reflected by the ultraviolet absorbance changes and visible color changes to the naked eye which was analyzed by Red-Green-Blue (RGB) data analysis via smartphone within 30 min, simplifying the detection process and shortening the detection time. Meanwhile, the dual targets-triggering mechanism and dual signal amplification strategy ensured detection specificity and sensitivity. Further, the practicability was verified by the detection of the real sample which provided this method an application potential in SARS-CoV-2 rapid detection.

Quantitative Determination of Staphylococcus aureus Using Aptamer-Based Recognition and DNA Amplification Machinery

Staphylococcus aureus (S. aureus) is a common foodborne pathogen that threatens human health and safety. It is significant to develop sensitive detection methods for the monitoring of S. aureus contamination in food and environment. Herein, a novel machinery based on aptamer recognition, DNA walker, and rolling circle amplification (RCA) was designed, which can form unique DNA nanoflower and subsequently detect low-level S. aureus contamination in samples. To this end, two rationally designed DNA duplexes were modified on the surface of the electrode to identify S. aureus through the high affinity between aptamers and S. aureus. Combined with the repeated movement of DNA walker machinery on the electrode surface and RCA technology, a unique DNA nanoflower structure was formed. This can effectively transform the biological information of aptamer recognition of S. aureus into a significantly amplified electrochemical signal. Through reasonable design and optimization of the parameters of each part, the linear response range of the S. aureus biosensor is from 60 to 6 × 10⁷ CFU/mL and the detection limit is as low as 9 CFU/mL.

MnO2 nanosheet-mediated generalist probe: Cancer-targeted dual-microRNAs detection and enhanced CDT/PDT synergistic therapy

While integrated nanoplatform for diagnosis and therapy has received much recent interest, its widespread application has been hampered by the complicated preparation process, high-cost and low-efficacy. Herein, we designed a MnO₂ nanosheet-mediated generalist probe (MNSGP), for intracellular dual-microRNAs (miRNAs) imaging and enhanced synergistic therapy of chemodynamic therapy (CDT) and photodynamic therapy (PDT). Because MNSGP can specifically target nucleolin receptor overexpressed on the cancer cell surface, it can be internalized via a receptor-mediated endocytosis pathway. After entering the cells, MnO₂ NS was degraded to Mn²⁺ by the excessive glutathione (GSH), releasing the DNA probes for cyclic amplification detection of miR-155 and miR-21 based on toehold-mediated strand displacement amplification (TSDA). Meanwhile, the produced O₂ by MnO₂ NS catalysis can promote the photosensitizer TMPyP4 to produce singlet oxygen (¹O₂) for PDT. The degraded Mn²⁺, as Fenton reagent, can convert endogenous H₂O₂ to cytotoxic hydroxyl radical (·OH) for CDT. In addition, the depletion of GSH impairs the antioxidant defense system (ADS), enhancing the CDT/PDT synergistic effect. The prepared generalist probe was fully characterized. Accuracy of dual-miRNAs detection and the high curative effect of enhanced CDT/PDT synergistic therapy were attested via in vitro and in vivo experiments. Unarguably, MNSGP broadens new horizons in the design of nucleic acid nanoplatform, cancer-targeted detection and theranostic application.

An ultrasensitive fluorescence detection template of pathogenic bacteria based on dual catalytic hairpin DNA Walker@Gold nanoparticles enzyme-free amplification

Integrating the advantages of catalytic hairpin components and multi-foot DNA walker, we designed a 16S rRNA detection probe template for pathogen bacteria, which utilizes DNA ligation quencher and dual catalytic hairpin@DNA walker to induce signal recovery. The dual catalytic hairpin@DNA walker uses the walking position of the target on the AuNP as a foothold to promote the reaction, so that the biosensing of the low-abundance target sequence can induce signal recovery. During the entire experiment, no enzyme is required, which can avoid the limitation of enzyme degradation under unfavorable conditions and the inability to detect the target. Most importantly, the detection template has the advantages of high sensitivity, and its detection limit is significantly better than that of single hairpin DNA walker probe. As the detection system can sensitively and rapidly detect its targeted bacteria and not rely on any enzyme and sophisticated instrumentation, it has great potential for sensitive and specific pathogenic bacteria detection.

Construction of Fast-Walking Tetrahedral DNA Walker with Four Arms for Sensitive Detection and Intracellular Imaging of Apurinic/Apyrimidinic Endonuclease 1

Herein, a novel tetrahedral DNA walker with four arms was engineered to travel efficiently on the 3D-tracks via catalyzed hairpin assembly autonomously, realizing the sensitive detection and activity assessment as well as intracellular imaging of apurinic/apyrimidinic endonuclease 1 (APE1). In contrast to traditional DNA walkers, the tetrahedral DNA walker with the rigid 3D framework structure and nonplanar multi-sites walking arms endowed with high collision efficiency, showing a fast walking rate and high nuclease resistance. Impressively, the initial rate of the tetrahedral DNA walker with four arms was 4.54 times faster than that of the free bipedal DNA walker and produced a significant fluorescence recovery in about 40 min, achieving a sensitive detection of APE1 with a low detection limit of 5.54× 10^-6 U/μL as well as ultrasensitive intracellular APE1 fluorescence activation imaging. This strategy provides a novel DNA walker for accurate identification of low-abundance cancer biomarker and potential medical diagnosis.

A nonlinear neural network based on an analog DNA toehold mediated strand displacement reaction circuit

The DNA toehold mediated strand displacement reaction is one of the semi-synthetic biology technologies for next-generation computers. In this article, we present a framework for a novel nonlinear neural network based on an engineered biochemical circuit, which is constructed by several reaction modules including catalysis, degradation and adjustment reaction modules. The proposed neural network possesses an architecture that is similar to that of an error back propagation neural network, and is built of an input layer, hidden layer and output layer. As a proof of concept, we utilize this nonlinear neural network based on an analog DNA toehold mediated strand displacement reaction circuit to learn the standard quadratic form function and analyze the robustness of the nonlinear neural network toward DNA strand concentration detection, DNA strand displacement reaction rate and noise. Unlike in error back propagation neural networks, the adaptive behavior of this DNA molecular neural network system endows it with supervised learning capability. This investigation will highlight the potential of analog DNA displacement reaction circuits for implementing artificial intelligence.

Recent Progress in Rapid Determination of Mycotoxins Based on Emerging Biorecognition Molecules: A Review

Mycotoxins are secondary metabolites produced by fungal species, which pose significant risk to humans and livestock. The mycotoxins which are produced from Aspergillus, Penicillium, and Fusarium are considered most important and therefore regulated in food- and feedstuffs. Analyses are predominantly performed by official laboratory methods in centralized labs by expert technicians. There is an urgent demand for new low-cost, easy-to-use, and portable analytical devices for rapid on-site determination. Most significant advances were realized in the field bioanalytical techniques based on molecular recognition. This review aims to discuss recent progress in the generation of native biomolecules and new bioinspired materials towards mycotoxins for the development of reliable bioreceptor-based analytical methods. After brief presentation of basic knowledge regarding characteristics of most important mycotoxins, the generation, benefits, and limitations of present and emerging biorecognition molecules, such as polyclonal (pAb), monoclonal (mAb), recombinant antibodies (rAb), aptamers, short peptides, and molecularly imprinted polymers (MIPs), are discussed. Hereinafter, the use of binders in different areas of application, including sample preparation, microplate- and tube-based assays, lateral flow devices, and biosensors, is highlighted. Special focus, on a global scale, is placed on commercial availability of single receptor molecules, test-kits, and biosensor platforms using multiplexed bead-based suspension assays and planar biochip arrays. Future outlook is given with special emphasis on new challenges, such as increasing use of rAb based on synthetic and naïve antibody libraries to renounce animal immunization, multiple-analyte test-kits and high-throughput multiplexing, and determination of masked mycotoxins, including stereoisomeric degradation products.

Signal enhancing strategies in aptasensors for the detection of small molecular contaminants by nanomaterials and nucleic acid amplification

Small molecular contaminants (such as mycotoxins, antibiotics, pesticide residues, etc.) in food and environment have given rise to many biological and ecological toxicities, which has attracted worldwide attention in recent years. Meanwhile, due to the advantages of aptamers such as high specificity and stability, easy synthesis and modification, as well as low cost and immunogenicity, various aptasensors for the detection of small molecular contaminants have been flourishing. An aptasensor as a whole is composed of an aptamer-based target recognizer and a signal transducer, which are fields of concentrated research. In the practical detection applications, in order to achieve the quantitative detection of small molecular contaminants at low abundance in real samples, a large number of signal enhancing strategies have been utilized in the development of aptasensors. Recent years is a vintage period for efficient signal enhancing strategies of aptasensors by the aid of nanomaterials and nucleic acid amplification that are applied in the elements for target recognition and signal conversion. Therefore, this paper meticulously reviews the signal enhancing strategies based on nanomaterials (including the (quasi-)zero-dimensional, one-dimensional, two-dimensional and three-dimensional nanomaterials) and nucleic acid amplification (including enzyme-assisted nucleic acid amplification and enzyme-free nucleic acid amplification). Furthermore, the challenges and future trends of the abovementioned signal enhancing strategies for application are also discussed in order to inspire the practitioners in the research and development of aptasensors for small molecular contaminants.

Sensitive detection of hepatitis C virus using a catalytic hairpin assembly coupled with a lateral flow immunoassay test strip

Currently, PCR is the gold standard for the detection of hepatitis C virus (HCV). However, the PCR technique is complicated and time-consuming, which prevents its application and, clinical point-of-care testing (POCT). Herein, we report a POCT method with simplicity, high sensitivity and specificity, which consists of a catalytic hairpin assembly (CHA) signal amplification system coupled with a lateral flow immunochromatographic (LFIA) test strip for the detection of HCV. Two ingeniously designed hairpin probes were hybridized to form the H1-H2 duplex in the presence of the target DNA. The catalytic hairpin assembly which was characterized of isothermal and enzyme-free, was accomplished within 40 min and the reaction was then applied to a LFIA test strip. Only the H1-H2 duplex labeled with both digoxin and biotin could be captured by the test strip, and the fluorescence value was determined. In addition, we evaluated the application potential for the detection of clinical samples. The reported method demonstrated high sensitivity with a detectable minimum concentration at 1 fM and showed a good linear range from 10 nM to 10pM, and high specificity for various mismatched sequences. The results demonstrated that clinically positive samples could be successfully detected. In conclusion, the reported method is simple, rapid, and free of large-scale equipment. POCT is expected to be useful for HCV detection in clinic.

3D DNA Walker-Assisted CRISPR/Cas12a Trans-Cleavage for Ultrasensitive Electrochemiluminescence Detection of miRNA-141

In this study, a CRISPR/Cas12a (LbCpf1)-mediated electrochemiluminescence (ECL) paper-based platform on the basis of a three-dimensional (3D) DNA walker was proposed for the ultrasensitive detection of miRNA-141. Initially, 3D-rGO with a tremendous loading space was modified on the paper working electrode (PWE) to construct an excellent conductive substrate and facilitate the growth of AuPd nanoparticles (NPs). Afterward, the AuPd NPs were introduced as the coreaction emitter medium of the 3D-rGO/PWE to provide convenience for the transformation between S₂O₈^2- and SO₄^2-, amplifying the ECL emission of g-C₃N₄ nanosheets (NSs). Meanwhile, with the help of Nt.BsmAI nicking endonuclease, a 3D DNA walker signal amplifier was designed to convert and magnify the target miRNA-141 into a particular trigger sequence, which could act as activator DNA to motivate the trans-acting deoxyribonuclease activity of CRISPR/Cas12a to further achieve efficient annihilation of the ECL signal. Furthermore, the proposed multimechanism-driven biosensor exhibited excellent sensitivity and specificity, with a relatively low detection limit at 0.331 fM (S/N = 3) in the concentration range between 1 fM and 10 nM. Consequently, the designed strategy not only extended the application scope of CRISPR/Cas12a but also devoted a new approach for the clinical diagnosis of modern medicine.

Accurate and Nonpurified Identification of Extracellular Vesicles Using Dual-Binding Recognition Mode

Circulating extracellular vesicles (EVs) are promising biomarkers for the early diagnosis and prognosis of cancer in a non-invasive manner. However, the rapid and accurate identification of EVs in complex biological samples is technically challenging, which is attributed to the requirement of extensive sample purification and unsatisfactory detection accuracy due to the disturbance of interfering proteins. Herein, a simultaneous binding of double-positive EV membrane protein-based recognition mode (DRM) is proposed. By the combination of DRM-mediated toehold activation and G-quadruplex DNAZyme-catalyzed etching of Au@Ag nanorods (Au@Ag NRs), we have developed an accurate, non-purified, low-cost, and visual strategy for EV identification. The synchronous binding of double-positive proteins on EV membranes is validated by confocal laser scanning microscopy analysis. This approach exhibits excellent specificity and sensitivity toward EVs ranging from 1.0 × 10⁵ to 1.0 × 10⁹ particles/mL with a detection limit of 6.31 × 10⁴ particles/mL. Moreover, we have successfully realized non-purified EV quantification in complex biological media. In addition, target-initiated catalyzed hairpin assembly (CHA) is integrated with G-quadruplex DNAZyme-catalyzed color variation of Au@Ag NRs; thus, low-background EV detection can be achieved by the naked eye. Furthermore, our strategy is easy to adapt to high-throughput formats by using an automatic microplate reader, which could be expected to meet the requirements for high-throughput detection of clinical samples. With its capacities of rapidness, portability, affordability, high throughput, non-purification, and visual detection, this strategy could provide a practical tool for accurate identification of EVs and early diagnosis of cancer.

Label-Free and Sensitive Electrochemical Biosensor for Amplification Detection of Target Nucleic Acids Based on Transduction Hairpins and Three-Leg DNAzyme Walkers

Nucleic acids are regarded as reliable biomarkers for the early diagnosis of various diseases. By ingeniously combining a transduction hairpin (THP) with the toehold-mediated strand displacement reaction (TSDR) to form three-leg DNAzyme walkers, for the first time, we constructed a label-free and sensitive electrochemical sensing system for the amplification detection of target nucleic acids. With microRNA-155 (miR-155) as a model target, the feasibility of the biosensing strategy and the conformational states of DNA in the recognition process were studied in detail on the basis of electrochemical and dual polarization interferometry techniques. With the assistance of THP, miR-155 indirectly triggered the TSDR between three hairpins (H1, H2, and H3), then massive Mg2+-dependent three-leg DNAzyme walkers were formed in aqueous solutions. After the binding/cleaving/moving process of three-leg DNAzyme walkers on the electrode surface modified with substrate hairpins (SHPs), a number of single-stranded DNAs (ssDNAs) were generated. Hence, the interaction of methylene blue (MB) with the duplex section of SHPs was impeded, which brought about a decreased electrochemical signal. Benefiting from the cyclic amplification of the TSDR and the higher cleavage activity of three-leg DNAzyme walkers, the proposed sensing strategy showed remarkable improvement in sensitivity with a low detection limit of 0.27 fM for miR-155. Owing to the precise design of the THP, this method exhibited excellent specificity to distinguish miR-155 from the single-base and triplex-base mismatched sequences. This sensing strategy importing the flexible THP can be utilized to detect various nucleic acid biomarkers by only redesigning the THP without changing the main circuit or reporter constructs, showing the great versatility and potential for the early diagnostics and biological analysis.