Recent advances in cascade isothermal amplification techniques for ultra-sensitive nucleic acid detection

A portable microfluidic chip-based fluorescent and colorimetric aptasensor combining recombinase polymerase amplification for bovine pregnancy-associated glycoproteins detection

A portable dual-mode PDMS-based microfluidic chip aptasensor was developed to detect bovine pregnancy-associated glycoproteins (bPAG) in bovine milk. Reagents within the chip chambers underwent reactions driven by gravity, where pre-encoded rich C sequences on the complementary strand of the aptamer facilitated the generation of abundant G-quadruplexes via subsequent RPA reaction, which activated the chromogenic substrates and fluorogenic precursors in the chip, producing distinct colorimetric and fluorescent signals. These signals were captured by our developed smartphone application and converted into RGB values, further enabling the quantification of bPAG with detection limits of 0.079 ng/mL and 0.024 ng/mL for colorimetric and fluorescent modes, respectively, over a linear range of 0.1-100 ng/mL. Bovine milk and other animal source milk were evaluated in the proposed assay, accurate identification results were obtained, indicating significant potential in bovine milk monitoring. The work further provided a valuable reference for point-of-care testing of non-nucleic acid targets in food samples.

Construction of fluorescent biosensor based on aptamer recognition and enzyme-free nucleic acid signal amplification reaction and its application in cocaine detection

Cocaine is a white crystalline alkaloid extracted from coca leaf. It can block human nerve conduction, produce local anesthetic effect, and has strong addiction. Therefore, the qualitative and quantitative analysis of cocaine is of great significance in forensic toxicology, pharmacy and metabolomics. Cocaine aptamer probe is expected to become a powerful tool for on-site detection of cocaine due to its good stability, fast response speed, and easy preparation of kits for on-site application. In our work, we construct a fluorescent biosensor for the detection of cocaine by using the characteristics of specific binding of nucleic acid aptamers to targets and combining with enzyme-free nucleic acid signal amplification reaction. First, streptavidin-modified magnetic beads (MBs) can specifically bind to biotin-modified cocaine aptamer probe (Aptamer) to form MB-DNA. The nucleic acid aptamer complementary probe (tDNA) can hybridize with the aptamer through base complementary pairing to form a double strand, thereby obtaining the MB-DNA-tDNA complex. When cocaine is present in the system, cocaine specifically binds to aptamer, thereby replacing the probe tDNA. The probe tDNA can undergo hybridization chain reaction with the hairpin probe 1 (HP1) and hairpin probe 2 (HP2), resulting in the opening of the hairpin structure, and the fluorescence signal response of the fluorophore 6-carboxyfluorescein (FAM) modified on the HP1 is turned on, so as to achieve rapid, low-cost and efficient cocaine detection. The establishment of this method can enrich and develop the basic theory of drug analysis and detection, and provide theoretical guidance and technical support for the accurate, efficient and convenient detection of drug analysis methods on site.

New sensing methods using commercially available products: Based on PGM and PTS

In recent years, detection technology has made remarkable progress in the field of food safety, in vitro diagnosis, and environment monitoring under the impetus of trace substances detection requirements. However, in sharp contrast to the rapid development of detection technology, its marketization process is relatively lagging behind. One possible approach is to integrate novel sensing strategies with mature commercial devices, such as personal glucose meters (PGMs) and pregnancy test strips (PTS) to speed up their marketization process. In this review, we systematically summarized design principle, evolution, and application progress for the integration of novel sensing strategies with commercial devices PGMs and PTS. Meanwhile, key factors and difficulties for the integration novel sensing strategies with commercial devices were emphasized. More importantly, the future of prospects and remaining challenges were discussed.

A simple "mix-and-detection" method based on template-free amplification for sensitive measurement of human cellular FEN1

Flap endonuclease 1 (FEN1) is a structure-specific nuclease that can specially identify and cleave 5' flap of branched duplex DNA, and it plays a critical role in DNA metabolic pathways and human diseases. Herein, we propose a simple "mix-and-detection" strategy for sensitive measurement of human cellular FEN1 on basis of template-free amplification. We design a dumbbell probe with 5' flap as a substrate of FEN1 and a NH2-labeled 3' termini to prevent nonspecific amplification. When FEN1 is present, the 5' flap is cleaved to release a free 3'-OH termini, initiating Ribonuclease HII (RNase HII)-assisted terminal deoxynucleotidyl transferase (TdT)-induced amplification for the production of a significant fluorescence signal. Due to the high exactitude of TdT-mediated extension reaction and RNase HII-induced single ribonucleotide excise, this assay shows excellent specificity and high sensitivity with a detection limit of 5.64 × 10-6 U/μL. Importantly, it can detect intracellular FEN1 activity with single-cell sensitivity under isothermal condition in a "mix-and-detection" manner, screen the FEN1 inhibitors, and even discriminate tumor cells from normal cells, offering a new platform for disease diagnosis and drug discovery.

Novel Multimode Assay Based on Asymmetrically Competitive CRISPR and Raman Barcode Spectra for Multiple Hepatocellular Carcinoma Biomarkers Detection

Commercial pregnancy test strips (PTS) possess the advantages of lower price, higher stability, and better repeatability and have been popularized to integrate with novel sensing strategies to detect other disease biomarkers, which accelerates the commercialization process of those novel sensing strategies. However, the current integration of novel sensing strategies into commercial PTS still faced the problems of insufficient quantification, low sensitivity, and lack of multiple detection capabilities. Hence, we proposed the concept of "visual classification recognition, spectral signal subdivision" for multiple hepatocellular carcinoma biomarkers (miRNA122 and miRNA233) detection with dual signals based on asymmetric competitive CRISPR (acCRISPR) and surface-enhanced Raman spectroscopy coupling with PTS, named the acCRISPR-PTS-SERS assay. In this assay, acCRISPR was used as a nonamplified cascaded signal amplification method to improve the sensitivity of detection. Two AuNPs-based core-shell Raman tags, each corresponding to different miRNA biomarkers, were used to achieve both visual recognition and spectral segmentation to enhance the quantification of PTS detection and the capability for multiple detection. Under the optimal conditions, the LOD for miRNA122 and miRNA223 were 10.36 and 4.65 fM, respectively. The sensitivity was enhanced by nearly 2 orders of magnitude. In the future, simultaneous hand-held detection for fingerprint barcodes of different cancers can be achieved with the assistance of a microfluidic chip and smartphone.

Excitation/emission-enhanced heterostructure photonic crystal array synergizing with "DD-A" FRET entropy-driven circuit for high-resolution and ultrasensitive analysis of ctDNA

Circulating tumor DNA (ctDNA) is an emerging biomarker of liquid biopsy for cancer. But it remains a challenge to achieve simple, sensitive and specific detection of ctDNA because of low abundance and single-base mutation. In this work, an excitation/emission-enhanced heterostructure photonic crystal (PC) array synergizing with entropy-driven circuit (EDC) was developed for high-resolution and ultrasensitive analysis of ctDNA. The donor donor-acceptor FÖrster resonance energy transfer ("DD-A" FRET) was integrated in EDC based on the introduction of simple auxiliary strand, which exhibited higher sensitivity than that of traditional EDC. The heterostructure PC array was constructed with the bilayer periodic nanostructures of nanospheres. Because the heterostructure PC has the adjustable dual photonic band gaps (PBGs) by changing nanosphere sizes, and the "DD-A" FRET can offer the excitation and emission peak with enough distance, it helps the successful matches between the dual PBGs of heterostructure PC and the excitation/emission peaks of "DD-A" FRET; thus, the fluorescence from EDC can be enhanced effectively from both of excitation and emission processes on heterostructure PC array. Besides, high-resolution of single-base mutation was obtained through the strict recognition of EDC. Benefiting from the specific spectrum-matched and synergetic amplification of heterostructure PC and EDC with "DD-A" FRET, the proposed array obtained ultrasensitive detection of ctDNA with LOD of 12.9 fM, and achieved the analysis of mutation frequency as low as 0.01%. Therefore, the proposed strategy has the advantages of simple operation, mild conditions (enzyme-free and isothermal), high-sensitivity, high-resolution and high-throughput analysis, showing potential in bioassay and clinical application.

Ultra-sensitive detection of SARS-CoV-2 S1 protein by coupling rolling circle amplification with poly(N-isopropylacrylamide)-based sandwich-type assay

In the past few years, the COVID-19 pandemic, caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) seriously threatens global public health security due to its high contagiousness. It remains of vital importance to develop a rapid and sensitive assay for SARS-CoV-2. In this work, we proposed a sandwich-type assay based on poly(N-isopropylacrylamide) (PNIPAM), allowing efficient detection of the SARS-CoV-2 S1 protein in the homogeneous solution. Firstly, a direct sandwich-type assay was established with a linear range of 0.2-2 μg/mL and a limit of detection (LOD) of 0.11 μg/mL, which could realize rapid detection in about 1 h. Furthermore, the sandwich-type assay coupled with rolling circle amplification (RCA) obtained an increase in sensitivity of 5.9 × 104 folds with a wide linear range of 0.01 - 100 ng/mL and a LOD of 1.88 pg/mL. The average recoveries in unpretreated saliva were 90 %-113.0 %, indicating the potential of the developed method for application in practical samples. Given the high selectivity and sensitivity of the developed method, it has a significant potential for rapid and early detection of SARS-CoV-2.

Rapid and sensitive detection of Mycobacterium tuberculosis using nested multi-enzyme isothermal rapid amplification in a single reaction

Tuberculosis (TB) remains a major global health problem, and there is an urgent need for rapid, sensitive, and easy-to-use diagnostic technologies to improve TB diagnosis. In this study, we developed the nested multi-enzyme isothermal rapid amplification (nestMIRA) assay for TB. We designed several pairs of primers and probes targeting the IS6110 sequence of Mycobacterium tuberculosis (Mtb) and performed combinatorial testing to optimize the performance of the TB nestMIRA assay. The reaction can be performed at a constant temperature of approximately 40°C and completed within 30 minutes in the same tube without opening the central cap. There has been no cross-reactivity with common non-tuberculous mycobacteria (NTB) and respiratory pathogens. The TB nestMIRA assay has a minimum detection limit of 5 copies/μL for H37Rv genomic DNA and a limit of quantification of 100 CFU/ml. To test the diagnostic performance of the TB nestMIRA assay, we conducted a 163-person clinical cohort study using comprehensive reference standards as the gold standard for clinical diagnosis. Our study showed that TB nestMIRA performed slightly better than GeneXpert MTB/RIF (Xpert) (85.27% vs. 82.17%) and significantly better than culture (55.81%) and acid-fast bacillus (AFB) smear (38.76%). The TB nestMIRA assay offers speed, specificity, sensitivity, and convenience. We believe that it has the potential to be a rapid alternative for TB diagnosis, particularly in resource-limited settings.

IMPORTANCE

In this study, we have successfully developed a method called nested multi-enzyme isothermal rapid amplification (nestMIRA) for the detection of Mycobacterium tuberculosis (Mtb). This method involves a two-step thermostatic amplification process in the same tube and can be read using fluorescence and lateral flow dipstick (LFD) assays. It is known to be rapid, specific, and highly sensitive. Our method has shown promising results in the detection of clinical specimens, and we believe that it can be a valuable tool for the rapid detection of Mtb in a clinical setting.

An RPA-Based CRISPR/Cas12a Assay in Combination with a Lateral Flow Assay for the Rapid Detection of Shigella flexneri in Food Samples

Among the pathogens that cause infectious diarrhea in China, Shigella is the most prominent. Shigellosis affects both adults and children, particularly those in developing nations, with nearly 190 million annual cases and a third resulting in fatalities. The recently emerged CRISPR/Cas system has also been increasingly applied for the detection of different biological targets. The lateral flow assay (LFA) has the advantages of short detection time, simple operation, high sensitivity, and low cost, and it provides an ideal platform for on-site detection. In this study, a recombinase polymerase amplification-CRISPR/Cas12a-LFA test for Shigella flexneri was constructed. The established method had good specificity and sensitivity, and the qualitative accuracy of 32 tested strains reached 100%. The detection limit of genomic DNA reached 8.3 copies/μL. With the advantages of high accuracy and portability, this diagnostic apparatus represents a novel method of identification and detection of Shigella flexneri, particularly in settings that lack complex laboratory infrastructure.

Diagnosis of Human Endemic Mycoses Caused by Thermally Dimorphic Fungi: From Classical to Molecular Methods

Human endemic mycoses are potentially fatal diseases caused by a diverse group of fungi that can alter their morphology in response to an increase in temperature. These thermally dimorphic fungi affect both healthy and immunocompromised hosts, causing a substantial health and economic burden. Despite this, the diagnosis of endemic mycoses is still a formidable challenge for several reasons, including similar symptomatology, limited utility of classical diagnostic methods, inaccessibility to reliable molecular approaches in most endemic areas, and a lack of clinical suspicion out of these regions. This review summarizes essential knowledge on thermally dimorphic fungi and the life-threatening diseases they cause. The principle, advantages and limitations of the methods traditionally used for their diagnosis are also described, along with the application status and future directions for the development of alternative diagnostic strategies, which could help to reduce the disease burden in endemic areas.

Hybrid chain reaction nanoscaffold-based functional nucleic acid nanomaterial cascaded with rolling circle amplification for signal enhanced miRNA let-7a detection

A novel functional nucleic acid (FNA) nanomaterial based on hybrid chain reaction (HCR) nanoscaffolds is proposed to solve the problem of time superposition and repeated primer design in sensitive miRND detection using cascade amplification technique. Rolling circle amplification (RCA) was cascaded with the prepared FNA nanomaterials for miRNA let-7a (as a model target) sensitive detection by lateral flow assay (LFA). Under the optimal conditions, the proposed RCA-FNA-LFA assay demonstrated the specificity and accuracy for miRNA let-7a detection with a detection limit of 1.07 pM, which increased sensitivity by nearly 20 times compared with that of RCA -LFA assay. It is worth noting that the non-target-dependent self-assembly process of HCR nanoscaffolds does not take up the whole detection time, thus, less time is taken than that of the conventional cascaded method. Moreover, the proposed assay does not need to consider the system compatibility between two kinds of isothermal amplification techniques. As for detection of different miRNAs, only the homologous arm of the padlock probe of RCA needs to be changed, while the FNA nanomaterial does not need any change, which greatly simplifies the primer design of the cascaded amplification techniques. With further development, the proposed RCA-FNA-LFA assay might achieve more sensitive and faster results to better satisfy the requirements of clinical diagnosis combing with more sensitive labels or small strip reader.

A quadratic isothermal amplification fluorescent biosensor without intermediate purification for ultrasensitive detection of circulating tumor DNA

Circulating tumor DNA (ctDNA) is an auspicious tumor biomarker released into the bloodstream by tumor cells, offering abundant information concerning cancer genes. It plays a crucial role in the early diagnosis of cancer. However, due to extremely low levels in body fluids, achieving a simple, sensitive, and highly specific detection of ctDNA remains challenging. Here, we constructed a purification-free fluorescence biosensor based on quadratic amplification of ctDNA by combining nicking enzyme mediated amplification (NEMA) and catalytic hairpin assembly (CHA) reactions. After double isothermal amplification, this biosensor achieved an impressive signal amplification of nearly 107-fold, enabling it to detect ctDNA with ultra-sensitivity. And the detection limit of this biosensor is as low as 2 aM. In addition, we explored the influence of human serum on the performance of the biosensor and found that it showed favorable sensitivity in the presence of serum. This biosensor eliminates the need for an intermediate purification step, resulting in enhanced sensitivity and convenience. Thus, our purification-free fluorescent biosensor exhibits ultra-high sensitivity when compared to other biosensors and has the potential to serve as an effective diagnostic tool for early detection of cancer.

Triplex DNA-based aggregation-induced emission probe: A new platform for hybridization chain reaction-based fluorescence sensing assay

The hybridization chain reaction (HCR), as one of the nucleic acid amplification technologies, is combined with fluorescence signal output with excellent sensitivity, simplicity, and stability. However, current HCR-based fluorescence sensing methods still have some defects such as the blocking effect of the HCR combination with fluorophores and the aggregation-caused quenching (ACQ) phenomenon of traditional fluorophores. Herein, a triplex DNA-based aggregation-induced emission probe (AIE-P) was designed as the fluorescent signal transduction, which is able to provide a new platform for HCR-based sensing assay. The AIE-P was synthesized by attaching the AIE fluorophores to terminus of the oligonucleotide through amido bond, and captured the products of HCR to form triplex DNA. In this case, the AIE fluorophores were located in close proximity to generate fluorescence. This assay provided turn-on fluorescence efficiency with a high signal-to-noise ratio and excellent amplification capability to solve the shortcoming of HCR-based fluorescence sensing methods. It enabled sensitive detection of Vibrio parahaemolyticus in the range of 102-106 CFU mL-1, and with a low limit of detection down to 39 CFU mL-1. In addition, this assay expressed good specificity and practicability. The triplex DNA-based AIE probe forms a universal molecular tool for developing HCR-based fluorescence sensing methods.

Chemiluminescent plate assay of microRNA-155 coupled with catalytic hairpin assembly with oligonucleotide release (CHAOR)

A heterogeneous sensitive microRNA-155 assay based on a new isothermal amplification method, called catalytic hairpin assembly with oligonucleotide release (CHAOR), was developed. The principle of CHAOR was studied by non-denaturing electrophoresis. To detect the amplification product, a polyperoxidase-streptavidin conjugate (molar ratio 1:80) and an enhanced chemiluminescence reaction were used, which made it possible to increase assay sensitivity. The detection limit of microRNA-155 assay was 0.4 pM. The coefficient of variation of the chemiluminescent signal, formed upon the heterogeneous determination of miRNA-155, was less than 12 % within the working range. The efficiency of CHAOR as an amplification method was similar to that of traditional CHA, as miRNA-155 assays based on CHAOR and CHA had similar analytical parameters. In addition, the proposed assay was highly specific. Contrary to traditional CHA, CHAOR, one of whose products is a single-stranded oligonucleotide, can be used in analytical methods based on cascade amplification.

Multienzymatic disintegration of DNA-scaffolded magnetic nanoparticle assembly for malarial mitochondrial DNA detection

Early diagnosis of malaria can prevent the spread of disease and save lives, which, however, remains challenging in remote and less developed regions. Here we report a portable and low-cost optomagnetic biosensor for rapid amplification and detection of malarial mitochondrial DNA. Bioresponsive magnetic nanoparticle assemblies are constructed by using nucleic acid scaffolds containing endonucleolytic DNAzymes and their substrates, which can be activated by the presence of target DNA and self-disintegrated to release magnetic nanoparticles for optomagnetic quantification. Specifically, target molecules can induce padlock probe ligation and subsequent one-pot homogeneous cascade reactions consisting of nicking-enhanced rolling circle amplification, DNAzyme-assisted nucleic acid recycling, and strand-displacement-driven disintegration of the magnetic assembly. With an optimized magnetic actuation process for reaction acceleration, a detection limit of 1 fM can be achieved by the proposed biosensor with a total assay time of ca. 90 min and a dynamic detection range spanning 3 orders of magnitude. The robustness of the system was validated by testing target molecules spiked in 5% serum samples. Clinical sample validation was conducted by testing malaria-positive clinical blood specimens, obtaining quantitative results concordant with qPCR measurements.

Combination of nucleic acid amplification and CRISPR/Cas technology in pathogen detection

Major health events caused by pathogenic microorganisms are increasing, seriously jeopardizing human lives. Currently PCR and ITA are widely used for rapid testing in food, medicine, industry and agriculture. However, due to the non-specificity of the amplification process, researchers have proposed the combination of nucleic acid amplification technology with the novel technology CRISPR for detection, which improves the specificity and credibility of results. This paper summarizes the research progress of nucleic acid amplification technology in conjunction with CRISPR/Cas technology for the detection of pathogens, which provides a reference and theoretical basis for the subsequent application of nucleic acid amplification technology in the field of pathogen detection.

Target-triggered dual signal amplification based on HCR-enhanced nanozyme activity for the sensitive visual detection of Escherichia coli

The detection of foodborne pathogens is crucial for food hygiene regulation and disease diagnosis. Colorimetry has become one of the main analytical methods in studying foodborne pathogens due to its advantages of visualization, low cost, simple operation, and no complex instrument. However, the low sensitivity limits its applications in early identification and on-site detection for trace analytes. In order to overcome such a limitation, herein we propose a joint strategy featuring dual signal amplification based on the hybridization chain reaction (HCR) and DNA-enhanced peroxidase-like activity of gold nanoparticles (AuNPs) for the sensitive visual detection of Escherichia coli. Target bacteria bound specifically to the aptamer domain in the capture hairpin probe, exposing the trigger domain for HCR and forming the extended double-stranded DNA (dsDNA) structures. The peroxidase-like catalytic capacity of AuNPs can be enhanced significantly by dsDNAs with the sticky ends of dsDNAs being adsorbed on AuNPs and the rigidity of dsDNAs causing the spatial regulation of AuNP concentration. The intensity of the enhancement was linearly related to the number of target bacteria. With the above strategy, the detection limit of our colorimetric method for Escherichia coli was down to 28 CFU mL-1 within a short analytical time (50 min). This study provides a new perspective for the sensitive and visual detection of early bacterial contamination in foods.

DNA Polymerase I Large Fragment from Deinococcus radiodurans, a Candidate for a Cutting-Edge Room-Temperature LAMP

In recent years, the loop-mediated isothermal amplification (LAMP) technique, designed for microbial pathogen detection, has acquired fundamental importance in the biomedical field, providing rapid and precise responses. However, it still has some drawbacks, mainly due to the need for a thermostatic block, necessary to reach 63 °C, which is the BstI DNA polymerase working temperature. Here, we report the identification and characterization of the DNA polymerase I Large Fragment from Deinococcus radiodurans (DraLF-PolI) that functions at room temperature and is resistant to various environmental stress conditions. We demonstrated that DraLF-PolI displays efficient catalytic activity over a wide range of temperatures and pH, maintains its activity even after storage under various stress conditions, including desiccation, and retains its strand-displacement activity required for isothermal amplification technology. All of these characteristics make DraLF-PolI an excellent candidate for a cutting-edge room-temperature LAMP that promises to be very useful for the rapid and simple detection of pathogens at the point of care.

Rapid detection of Mycobacterium tuberculosis in sputum using CRISPR-Cas12b combined with cross-priming amplification in a single reaction

IMPORTANCE

In this study, we successfully established a new One-Pot method, named TB One-Pot, for detecting Mtb in sputum by combining CRISPR-cas12b-mediated trans-cleavage with cross-priming amplification (CPA). Our study evaluated the diagnostic performance of TB One-Pot in clinical sputum samples for tuberculosis. The findings provide evidence for the potential of TB One-Pot as a diagnostic tool for tuberculosis.

Ultrasensitive reporter DNA sensors built on nucleic acid amplification techniques: Application in the detection of trace amount of protein

The detection of protein is of great significance for the study of biological physiological function, early diagnosis of diseases and drug research. However, the sensitivity of traditional protein detection methods for detecting trace amount of proteins was relatively low. By integrating sensitive nucleic acid amplification techniques (NAAT) with protein detection methods, the detection limit of protein detection methods can be substantially improved. The DNA that can specifically bind to protein targets and convert protein signals into DNA signals is collectively referred to reporter DNA. Various NAATs have been used to establish NAAT-based reporter DNA sensors. And according to whether enzymes are involved in the amplification process, the NAAT-based reporter DNA sensors can be divided into two types: enzyme-assisted NAAT-based reporter DNA sensors and enzyme-free NAAT-based reporter DNA sensors. In this review, we will introduce the principles and applications of two types of NAAT-based reporter DNA sensors for detecting protein targets. Finally, the main challenges and application prospects of NAAT-based reporter DNA sensors are discussed.

Highly specific detection of Neisseria gonorrhoeae based on recombinase polymerase amplification-initiated strand displacement amplification

Neisseria gonorrhoeae is the only pathogen that causes gonorrhea, and can have serious consequences if left untreated. A simple and accurate detection method for N. gonorrhoeae is essential for the diagnosis of gonorrhea and the appropriate prescription of antibiotics. The application of isothermal recombinase polymerase amplification (RPA) to detect this pathogen is advantageous because of its rapid performance, high sensitivity, and minimal dependency on equipment. However, this simplicity is offset by the risk of false-positive signals from primer-dimers and primer-probe dimers. In this study, RPA-initiated strand displacement amplification (SDA) was established for the detection of N. gonorrhoeae, and eliminated false-positive signals from primer-dimers and primer-probe dimers. The developed biosensor allows for the reduced generation of nonspecific RPA amplification through the design of enzyme cleavage sites on primers, introduction of SDA, and detection of the final product using a molecular beacon (MB). Using this system, the DNA double strand is transformed into single-stranded DNA following SDA, thereby providing a more suitable binding substrate and improving the efficiency of MB detection. Amplification can be conducted below 37 °C, and the process can be completed within 90 min. The limit of detection was determined to be 0.81 copies/μL. This system is highly specific for N. gonorrhoeae and exhibits no cross-reactivity with other common urogenital pathogens. The results of this study are consistent with those of real-time PCR performed on clinical specimens of urogenital secretions. In summary, the biosensor is a simple and specific detection method for N. gonorrhoeae.

Programmable electrochemical biosensing platform based on catalytic hairpin assembly and entropy-driven catalytic cascade amplification circuit

Herein, powerful DNA strand displacement reaction and sensitive electrochemical analysis method were ingeniously integrated to develop a programmable biosensing platform. Using DNA as the detection model, a cascade amplification system based on catalytic hairpin assembly and entropy-driven catalytic was constructed, and the reaction rate and signal amplification effect were significantly improved. The product of the cascade amplification circuit could undergo strand displacement reaction with the signal probe on the electrode surface to obtain sensitive electrochemical signal changes and realize highly sensitive detection of the target. In addition, without redesigning the DNA sequences in the cascade amplification circuit, the by-product strand typically wasted in traditional entropy-driven catalytic reactions can be fully utilized to construct a single-signal output biosensing system and even a dual-signal output ratiometric biosensing platform, improving the detection repeatability and reliability of the system, and expanding the application of DNA strand displacement reaction in electrochemical biosensing. Furthermore, benefiting from the design flexibility of the DNA molecules, the constructed biosensing platform realized the sensitive detection of aptamer substrate (kanamycin as an example) and certain metal ion (mercury as an example) by simply recoding the corresponding recognition sequence, demonstrating the good versatility of the biosensing platform.