Ultrasensitive and Label-Free Detection of Multiple DNA Methyltransferases by Asymmetric Nanopore Biosensor

CRISPR/Cas12a Protein Switch Powered Label-Free Electrochemical Biosensor for Sensitive Viral Protease Detection

Viral proteases are critical molecular targets in viral pathogenesis, representing pivotal biomarkers for understanding viral infection mechanisms and developing antiviral therapeutics. This study introduces a label-free electrochemical biosensor that enables sensitive viral protease detection by integrating protease-responsive CRISPR/Cas protein switches (CasPSs) with a hemin aptamer-functionalized electrochemical interface. The biosensor's mechanism relies on viral protease-mediated proteolysis, which leads to the release of active Cas12a proteins from CasPSs and generates amplified electrochemical responses through continuous cleavage of immobilized redox-active hemin/aptamer complexes. This biosensor achieved specific hepatitis C virus NS3/4A protease sensing with femtomolar sensitivity and could be readily expanded to other viral proteases by replacing the CasPS module. The feasibility of this biosensor was demonstrated by monitoring enterovirus 71 3C protease activities in virus-infected cell samples with different viral loads and postinfection times. This study provides a promising strategy for integrating CRISPR biosensing with electrochemical platforms, offering a helpful analytical tool for viral infection monitoring and antiviral drug screening.

Nanopipettes for Chemical Analysis in Life Sciences

Nanopipette-based assays have gained widespread applications in electrochemical and analytical technologies, achieving significant advancements over the past decade in DNA sequencing, biosensing, targeted delivery, and bioimaging. The ultrasmall tip size of nanopipettes bridges the gap between the macro- and nano worlds, which can be attributed to the capability of nanopipettes to transport ultrasmall volumes of liquids, ions, and solutes. In this review, we discuss the fabrication, characterization, and modification of nanopipettes to provide an overview of the recent developments of nanopipette-based sensors and strategies. We also introduce the recent studies developed by our group and other groups using nanopipettes for chemical analysis of life science. Finally, we discuss the future development of nanopipette-based strategies and their exciting potential for studying bioscience and biomedical engineering.

DNAzyme-assisted the detection of rps27l mRNA in protein nanopores

Quantifying mRNA is crucial for elucidating the physiological condition of organisms in life science research and clinical diagnostics. Recently, nanopore technology has been demonstrated as a versatile tool with a myriad of applications and successful implementations for genomic analyte identification. However, its application in mRNA quantification encounters challenges such as the presence of numerous background species, low expression levels, and complex mRNA structures. Herein, we propose the implementation of a DNAzyme-assisted approach for rp27l mRNA quantification in MspA protein nanopores. The strategy involves converting the quantification of mRNA through a DNAzyme reaction, where the sequence of GR-5 DNAzyme is integrated into Probe 2 (P2). The sandwich structure (P1-T-P2) is constructed between the target molecules and two types of probes, enabling the identification of target molecules and the retention of the enzyme strand in magnetic fields. As a result, GR-5 DNAzyme not only effectively hydrolyzes the corresponding substrates to yield external probes for subsequent nanopore analysis but also functions as an ingenious molecular amplification method by persistently digesting excess substrates to produce abundant external probes. This sensor acquires the amplification capability and attains a high sensitivity with a detection limit of 40 pM within 15-min measurements, improving the sensitivity of protein nanopores for nucleic acid detection. Thus, the proposed DNAzyme-based protein nanopore sensor for rp27l mRNA quantification demonstrates remarkable advantages in its label-free, rapid, and sensitive nature, which promotes the performance of protein nanopores in genomic analyte detection. Moreover, this sensor may open a novel approach for mRNA quantification, significantly impacting disease diagnosis, customized treatment, and metabolic studies.

Ultrasensitive COFs Functionalized Electrochemical Biosensor for DNA Methyltransferase Activity Detection by DNA Walking and Rolled Circular Strand Displacement Amplification

Assessing the activity of DNA methyltransferases (MTases) and screening for methyltransferase inhibitors not only allow for a deep exploration of the role of methylation regulation in disease initiation and progression but also provide an important experimental and clinical basis for the diagnosis and treatment of diseases. Herein, a new COFs functionalized electrochemical biosensor has been developed to detect DNA adenine methylation (Dam) MTase activity with high sensitivity and rapidity by taking advantage of the DNA walker and rolled circular strand displacement amplification (RC-SDA) reaction. Specifically, hairpin probe H1 was methylated by Dam MTase, followed by methylation site-specific cleavage of DpnI enzyme to generate the S5 probe. The padlock probes with two nucleic acid endonuclease sites were introduced to trigger the RC-SDA reaction under the action of the primer, releasing a large number of single-stranded S6 probes. The released probe worked synergistically with the Exo III enzyme to trigger DNA walking, which exposed the binding sites to enable the Au-COF-MB signal probes to bind effectively to the electrode surface, and the electrochemical signals were thus generated. The result showed that the designed electrochemical biosensor demonstrated excellent sensitivity and specificity in detecting the activity of Dam MTase, with the detection limit (LOD) of 6.85 × 10-5 U/mL. This method provides support for the development of new treatment strategies for methylation related diseases.

Specific Response Assembly of 3D Space-Confined DNA Nanoaggregates for Rapid and Sensitive Detection of DNA Methyltransferase

Rapid and sensitive detection of DNA adenine methyltransferase (Dam) activity is crucial for both research and clinical applications. Herein, we utilize two types of spherical nucleic acids (SNAs) to specific response assemble into 3D space-confined DNA nanoaggregates that enable the rapid and sensitive detection of Dam activity. The SNAs feature 3D order DNA scaffolds that serve as cores for anchoring signal hairpin probes (S-HPs) and target hairpin probes (T-HPs). Specifically, two distinct S-HPs are labeled with FAM fluorophores and BHQ1 quenchers and share identical hairpin sequences, while two types of T-HPs are designed with different linking sequences and specific recognition regions, resulting in the formation of two types of SNAs (SNA1 and SNA2). In the presence of Dam, the recognition region of the T-HPs is methylated and subsequently cleaved by auxiliary endonuclease, releasing the loop of the T-HP as a walking strand and exposing the linking sequence on the SNAs. Notably, the prior design of complementary linking sequences in the two types of SNAs facilitates their assembly into 3D DNA nanoaggregates, creating a confined space for walking strands to recover fluorescent signals. The 3D DNA nanoaggregate system not only provides highly ordered tracks but also enhances the spatial continuity of the walking strands, greatly improving the reaction kinetics for detecting Dam activity. This strategy enables the rapid and sensitive detection of Dam activity within 105 min, achieving a limit of detection of 2.9 × 10-4 U mL-1, demonstrating significant potential for advancing research in DNA methylation.

Asymmetric Nanopore Sensor for Logic Detection of Dam and M.SssI Methyltransferases in Combination of DNA Walker and Autocatalytic Hybridization Reaction

The detection of DNA methyltransferase (MTase) was crucial for understanding gene expression regulation, cancer mechanisms, and various biological processes, contributing significantly to disease diagnosis and drug development. Herein, a nanopore sensor based on cascaded signal amplification of DNA walker and autocatalytic hybridization reaction (AHR) was developed for the ultrasensitive determination of various MTases. In the presence of Dam MTase, the hairpin structure HD underwent methylation and cleavage by DpnI endonuclease, forming T-DNA fragments. These T-DNA fragments were used to activate the DNA walker, which moved across the surface of magnetic beads step by step, generating a large quantity of initiator I by cleaving the substrate. The initiator I subsequently activated the AHR. The AHR included a hybridization chain reaction (HCR) amplifier and a catalytic hairpin assembly (CHA) convertor. The HCR amplifier generated multiple novel CHA triggers, which activated the CHA convertor. This, in turn, stimulated the HCR amplifier, creating an AHR circuit that resulted in the formation of numerous DNA nanowires. These DNA nanowires were adsorbed onto the G4-PAMAM-modified nanopore surface under the influence of an electric field, thereby altering the surface charge of the nanopore and changing the ionic rectification curve. The detection limit of the Dam MTase nanopore sensor reached 0.0002 U/mL. By modification of the recognition sites of the probes, this nanopore system could also be used for the detection of M.SssI MTase. Moreover, a four-input parallel concatenated logic circuit (AND//INHIBIT-OR) had been constructed and applied for the multivariate detection of Dam MTase and M.SssI MTase, presenting a novel conceptual model for advancing the construction of nanopore logic gate systems and their applications in biosensing.

SERS biosensors based on catalytic hairpin self-assembly and hybridization chain reaction cascade signal amplification strategies for ultrasensitive microRNA-21 detection

A highly sensitive surface-enhanced Raman scattering (SERS) biosensor has been developed for the detection of microRNA-21 (miR-21) using an isothermal enzyme-free cascade amplification method involving catalytic hairpin assembly (CHA) and hybridization chain reaction (HCR). The CHA reaction is triggered by the target miR-21, which causes hairpin DNA (C1 and C2) to self-assemble into CHA products. After AgNPs@Capture captures the resulting CHA product, the HCR reaction is started, forming long-stranded DNA on the surface of AgNPs. A strong SERS signal is generated due to the presence of a large amount of the Raman reporter methylene blue (MB) in the vicinity of the SERS "hot spot" on the surface of AgNPs. The monitoring of the SERS signal changes of MB allows for the highly sensitive and specific detection of miR-21. In optimal conditions, the biosensor exhibits a satisfactory linear range and a low detection limit for miR-21 of 42.3 fM. Additionally, this SERS biosensor shows outstanding selectivity and reproducibility. The application of this methodology to clinical blood samples allows for the differentiation of cancer patients from healthy controls. As a result, the CHA-HCR amplification strategy used in this SERS biosensor could be a useful tool for miRNA detection and early cancer screening.

Selective Activation of Cascade Assembly Amplification for DNA Methyltransferase Detection Using a Double-Loop Interlocked DNA Circuit

Precise and reliable monitoring of DNA adenine methyltransferase (Dam) activity is essential for disease diagnosis and biological analysis. However, existing techniques for detecting Dam activity often rely on specific DNA recognition probes that are susceptible to DNA degradation and exhibit limited target sensitivity and specificity. In this study, we designed and engineered a stable and dynamic DNA nanodevice called the double-loop interlocked DNA circuit (DOOR) that enables the sensitive and selective monitoring of Dam activity in complex biological environments. The DOOR incorporates two interlocked specialized sequences: a palindromic sequence for Dam identification and an initiator sequence for signal amplification. In the presence of Dam, the DOOR is cleaved by double-stranded DNA phosphodiesterase I endonuclease, generating massive double-stranded DNA (dsDNA) units. These units can self-assemble into a long dsDNA scaffold, thereby enhancing the subsequent reaction kinetics. The dsDNA scaffold further triggers a hyperbranched hybrid chain reaction to produce a fluorescent 3D DNA nanonet, enabling more precise monitoring of the Dam activity. The DOOR device exhibits excellent sensitivity, specificity, and stability, rendering it a powerful tool for studying DNA methylation in various biological processes and diseases.

Research progress of human key DNA and RNA methylation-related enzymes assay

Gene methylation-related enzymes (GMREs) are disfunction and aberrantly expressed in a variety of cancers, such as lung, gastric, and pancreatic cancers and have important implications for human health. Therefore，it is critical for early diagnosis and therapy of tumor to develop strategies that allow rapid and sensitive quantitative and qualitative detection of GMREs. With the development of modern analytical techniques and the application of various biosensors, there are numerous methods have been developed for analysis of GMREs. Therefore, this paper provides a systematic review of the strategies for level and activity assay of various GMREs including methyltransferases and demethylase. The detection methods mainly involve immunohistochemistry, colorimetry, fluorescence, chemiluminescence, electrochemistry, etc. Then, this review also addresses the coordinated role of various detection probes, novel nanomaterials, and signal amplification methods. The aim is to highlight potential challenges in the present field, to expand the analytical application of GMREs detection strategies, and to meet the urgent need for future disease diagnosis and intervention.

Solid-State Glass Nanopipettes: Functionalization and Applications

Solid-state glass nanopipettes provide a promising confined space that offers several advantages such as controllable size, simple preparation, low cost, good mechanical stability, and good thermal stability. These advantages make them an ideal choice for various applications such as biosensors, DNA sequencing, and drug delivery. In this review, we first delve into the functionalized nanopipettes for sensing various analytes and the methods used to develop detection means with them. Next, we provide an in-depth overview of the advanced functionalization methodologies of nanopipettes based on diversified chemical kinetics. After that, we present the latest state-of-the-art achievements and potential applications in detecting a wide range of targets, including ions, molecules, biological macromolecules, and single cells. We examine the various challenges that arise when working with these targets, as well as the innovative solutions developed to overcome them. The final section offers an in-depth overview of the current development status, newest trends, and application prospects of sensors. Overall, this review provides a comprehensive and detailed analysis of the current state-of-the-art functionalized nanopipette perception sensing and development of detection means and offers valuable insights into the prospects for this exciting field.

Importance of DNA nanotechnology for DNA methyltransferases in biosensing assays

DNA methylation is the process by which specific bases on a DNA sequence acquire methyl groups under the catalytic action of DNA methyltransferases (DNMT). Abnormal changes in the function of DNMT are important markers for cancers and other diseases; therefore, the detection of DNMT and the selection of its inhibitors are critical to biomedical research and clinical practice. DNA molecules can undergo intermolecular assembly to produce functional aggregates because of their inherently stable physical and chemical properties and unique structures. Conventional DNMT detection methods are cumbersome and complicated processes; therefore, it is necessary to develop biosensing technology based on the assembly of DNA nanostructures to achieve rapid analysis, simple operation, and high sensitivity. The design of the relevant program has been employed in life science, anticancer drug screening, and clinical diagnostics. In this review, we explore how DNA assembly, including 2D techniques like hybridization chain reaction (HCR), rolling circle amplification (RCA), catalytic hairpin assembly (CHA), and exponential isothermal amplified strand displacement reaction (EXPAR), as well as 3D structures such as DNA tetrahedra, G-quadruplexes, DNA hydrogels, and DNA origami, enhances DNMT detection. We highlight the benefits of these DNA nanostructure-based biosensing technologies for clinical use and critically examine the challenges of standardizing these methods. We aim to provide reference values for the application of these techniques in DNMT analysis and early cancer diagnosis and treatment, and to alert researchers to challenges in clinical application.

Bridging Ionic Current Rectification and Resistive-Pulse Sensing for Reliable Wide-Linearity Detection

As two mainstream ionic detection techniques, ionic current rectification (ICR) suffers from large fluctuations in trace level detection, while resistive-pulse sensing (RPS) encounters easy clogs in high-concentration detection. By rationally matching the nanopore size with the DNA tetrahedron (TDN), this work bridges the two techniques to achieve reliable detection with wide linearity. As a representative analyte, miRNA-10b could specifically combine with and release TDN from the interior wall, which thus induced the simultaneous generation of distinct ICR and RPS signals. The ICR signals could be attributed to the balance between the effective orifice and surface charge density of the inner wall, while the RPS signals were induced by the complex of miRNA-10b and TDN passing through the nanopore. Such an operation contributed to a wide detection range of 1 fM-1 nM with a good linearity. The feasibility of this method is also validated in single-cell and real plasma detection.

Plasmonic Gold Nanostar-Based Probes with Distance-Dependent Plasmon-Enhanced Fluorescence for Ultrasensitive DNA Methyltransferase Assay

The ultrasensitive DNA methyltransferase (Dam MTase) assay is of high significance for biomedical research and clinical diagnosis because of its profound effect on gene regulation. However, detection sensitivity is still limited by shortcomings, including photobleaching and weak signal intensities of conventional fluorophores at low concentrations. Plasmonic nanostructures with ultrastrong electromagnetic fields and fluorescence enhancement capability that can overcome these intrinsic defects hold great potential for ultrasensitive bioanalysis. Herein, a silica-coated gold nanostars (Au NSTs@SiO2)-based plasmon-enhanced fluorescence (PEF) probe with 20 "hot spots" was developed for ultrasensitive detection of Dam MTase. Here, the Dam Mtase assay was achieved by detecting the byproduct PPi of the rolling circle amplification reaction. It is worth noting that, benefiting from the excellent fluorescence enhancement capability of Au NSTs originating from their 20 "hot spots", the detection limit of Dam Mtase was reduced by nearly 105 times. Moreover, the proposed Au NST-based PEF probe enabled versatile evaluation of Dam MTase inhibitors as well as endogenous Dam MTase detection in GW5100 and JM110 Escherichia coli cell lysates, demonstrating its potential in biomedical analysis.

Portable Sensor for Aflatoxin B1 Based on the Regulation of Resistance of a Microchannel Using a Multimeter as Readout

Changes in the charge density on the inner surface of the microchannel can modulate the ion concentration at the tip, thus causing changes in the resistance of the system. In this study, this property is adopted to construct a portable sensor using a multimeter and aflatoxin B1 (AFB1) is used as the model target. Initially, the cDNA/aptamer complex is modified in the microchannel. The inner microchannel surface's charge density is then altered by the recognition of the target, leading to a change in the system's resistance, which can be conveniently monitored using a multimeter. Critical parameters influencing the performance of the system are optimized. Under optimum conditions, the resistance is linearly related to the logarithm of AFB1 concentration in the range of 100 fM-10 nM and the detection limit is 46 fM (S/N = 3). The resistive measurement is separated from the recognition reaction of the target, reducing the matrix interference during the detection process. This sensor boasts high sensitivity and specificity coupled with commendable reproducibility and stability. It is applied to assay the AFB1 content successfully in an actual sample of corn. Moreover, this approach is cost-effective, user-friendly, and highly accurate.

Solid-State Nanopores for Biomolecular Analysis and Detection

Advances in nanopore technology and data processing have rendered DNA sequencing highly accessible, unlocking a new realm of biotechnological opportunities. Commercially available nanopores for DNA sequencing are of biological origin and have certain disadvantages such as having specific environmental requirements to retain functionality. Solid-state nanopores have received increased attention as modular systems with controllable characteristics that enable deployment in non-physiological milieu. Thus, we focus our review on summarizing recent innovations in the field of solid-state nanopores to envision the future of this technology for biomolecular analysis and detection. We begin by introducing the physical aspects of nanopore measurements ranging from interfacial interactions at pore and electrode surfaces to mass transport of analytes and data analysis of recorded signals. Then, developments in nanopore fabrication and post-processing techniques with the pros and cons of different methodologies are examined. Subsequently, progress to facilitate DNA sequencing using solid-state nanopores is described to assess how this platform is evolving to tackle the more complex challenge of protein sequencing. Beyond sequencing, we highlight the recent developments in biosensing of nucleic acids, proteins, and sugars and conclude with an outlook on the frontiers of nanopore technologies.

Solid-State Nanopore Sensors with Enhanced Sensitivity through Nucleic Acid Amplification

Solid-state nanopores have wide applications in DNA sequencing, energy conversion and storage, seawater desalination, sensors, and reactors due to their high stability, controllable geometry, and a variety of pore-forming materials. Solid-state nanopore sensors can be used for qualitative and quantitative analyses of ions, small molecules, proteins, and nucleic acids. The combination of nucleic acid amplification and solid-state nanopores to achieve trace detection of analytes is gradually attracting attention. This review outlines nucleic acid amplification strategies for enhancing the sensitivity of solid-state nanopore sensors by summarizing the articles published in the past 10 years. The future development prospects and challenges of nucleic acid amplification in solid-state nanopore sensors are discussed. This review helps readers better understand the field of solid-state nanopore sensors. We believe that solid-state nanopore sensors will break through the bottleneck of traditional detection and become a powerful single-molecule detection platform.

Nanofluidic sensing platform for PNK assay using nonlinear hybridization chain reaction and its application in DNA logic circuit

In this study, a polyethyleneimine (PEI)/Zr4+-functionalized nanofluidic sensing platform based on nonlinear hybridization chain reaction (NHCR) was developed for PNK activity assay. With the existence of PNK, the hairpin HPNK was cleaved by λ exonuclease, liberating the initiator T-DNA. Then T-DNA triggered the nonlinear HCR in solution and the reaction products were absorbed onto the nanopore, which changed the surface charge of nanofluidic device and could be detected by current-voltage characteristic curves. Compared to traditional linear HCR, the nonlinear HCR exhibits a higher sensitivity and order of growth kinetics, making it a powerful signal amplifier in bioanalysis. Due to the powerful amplification efficiency of nonlinear HCR, high sensitivity of the nanopore and specific recognition site of PNK/λ-Exo, an ultrasensitive and selective PNK sensing approach had been developed and applied to precisely quantitate the PNK activity with a LOD of 0.0001 U/mL. Moreover, utilizing this nanofluidic system as a foundation, we constructed a logic circuit that utilized PNK, adenosine diphosphate (ADP), and (NH4)2SO4 as input elements. ADP and (NH4)2SO4 had a crucial function in facilitating the PNK to regulate the DNA logic gate. By modifying the target and inhibitors, the nanofluidic device could detect a variety of stimuli and execute more advanced logical operations.

Fluorescence turn-off strategy for sensitive detection of DNA methyltransferase activity based on DNA-templated gold nanoclusters

DNA methylation results in a variety of human diseases and the DNA methylation process is mediated by DNA methyltransferases, which have therefore become potential targets for disease treatment. In this study, a turn-off nanogold biological probe system was successfully created for determining the activity of DNA methyltransferases (M.SssI MTase). A dumbbell-shaped DNA probe with a site-recognizable region of M. SssI MTase and a fluorescent signal probe based on a DNA-templated gold nanocluster (DNA-AuNC) probe combined for the quantitative detection of M. SssI MTase. This dumbbell-shaped DNA probe was methylated by M. SssI MTase, and the dumbbell-shaped DNA probe with a methyl group was recognized by an endonuclease (GlaI) and cleaved into hairpin DNA. The dGTP was added to the 3'-OH terminus of hairpin DNA fragments in the presence of terminal deoxynucleotidyl transferase (TdT), and the hairpin DNA was extended with a G-rich sequence that can be used as an inactivation probe. When the inactivation probe was combined with the signal probe, the fluorescent signal disappeared due to the photoinduced electron transfer effect. Methyltransferase activity was then detected based on the turn-off principle of the fluorescence signal from the DNA-AuNCs. The bioprobe enabled sensitive detection of M. SssI MTase with a detection limit of 0.178 U mL^-1 and good specificity. The bioprobe demonstrated good detection efficiency in both human serum and cell lysates, and its unique fluorescence turn-off mechanism provided good resistance to interference, thus increasing its potential application in complex biological samples. Moreover, it is suitable for screening and assessing the inhibitory activity of M. SssI MTase inhibitors, and therefore has significant potential for disease diagnosis and drug discovery.

Nanopore Single-molecule Analysis of Biomarkers: Providing Possible Clues to Disease Diagnosis

Biomarker detection has attracted increasing interest in recent years due to the minimally or non-invasive sampling process. Single entity analysis of biomarkers is expected to provide real-time and accurate biological information for early disease diagnosis and prognosis, which is critical to the effective disease treatment and is also important in personalized medicine. As an innovative single entity analysis method, nanopore sensing is a pioneering single-molecule detection technique that is widely used in analytical bioanalytical fields. In this review, we overview the recent progress of nanopore biomarker detection as new approaches to disease diagnosis. In highlighted studies, nanopore was focusing on detecting biomarkers of different categories of communicable and noncommunicable diseases, such as pandemic Covid-19, AIDS, cancers, neurologic diseases, etc. Various sensitive and selective nanopore detecting strategies for different types of biomarkers are summarized. In addition, the challenges, opportunities, and direction for future development of nanopore-based biomarker sensors are also discussed.

Ultrasensitive fluorescence detection of multiple DNA methyltransferases based on DNA walkers and hyperbranched rolling circle amplification

The accurate and ultrasensitive detection of multiple methyltransferases was in great request for clinical diagnosis and epigenetic therapy. Here, a novel fluorescence assay was proposed for ultrasensitive CpG methyltransferase (M.SssI) and DNA adenine methyltransferase (Dam) activity detection based on hyperbranched rolling circle amplification (HRCA) and DNA walkers. The biosensor showed an extremely high sensitivity due to the dual-amplification strategy of HRCA and DNA walker. The LOD of the biosensor for M.SssI and Dam methyltransferase was estimated at 0.0004 U/mL and 0.001 U/mL, respectively. Without the presence of M.SssI methyltransferase, the corresponding recognition site of hairpin H_M was cleaved by HpaII endonuclease, generating a DNA fragment (T-DNA) and inducing the DNA walker-HRCA reaction. Since the HRCA products contained numerous double-strand DNA (dsDNA), SYBR Green I could be embedded in the dsDNA, leading to a high fluorescent signal. In the presence of M.SssI methyltransferase, the corresponding recognition site of hairpin H_M was methylated and the HpaII endonuclease-catalyzed stem of hairpin H_M dissociation was hindered, leading to no DNA fragment (T-DNA) present. Hence, the DNA walker-HRCA reaction was not initiated and the fluorescent signal of SYBR Green I remained at a low level. Similarly, DNA adenine methyltransferase (Dam) and its inhibitors could also be detected by redesigning hairpin H_D with the Dam recognition sequences. Furthermore, the sensing system was applied to analyze the endogenic Dam methyltransferase in the real samples such as E. coli cell lysate.

Solid-State Nanopore/Nanochannel Sensing of Single Entities

Solid-state nanopores/nanochannels, with their high stability, tunable geometry, and controllable surface chemistry, have recently become an important tool for constructing biosensors. Compared with traditional biosensors, biosensors constructed with solid-state nanopores/nanochannels exhibit significant advantages of high sensitivity, high specificity, and high spatiotemporal resolution in the detection single entities (such as single molecules, single particles, and single cells) due to their unique nanoconfined space-induced target enrichment effect. Generally, the solid-state nanopore/nanochannel modification method is the inner wall modification, and the detection principles are the resistive pulse method and the steady-state ion current method. During the detection process, solid-state nanopore/nanochannel is easily blocked by single entities, and interfering substances easily enter the solid-state nanopore/nanochannel to generate interference signals, resulting in inaccurate measurement results. In addition, the problem of low flux in the detection process of solid-state nanopore/nanochannel, these defects limit the application of solid-state nanopore/nanochannel. In this review, we introduce the preparation and functionalization of solid-state nanopore/nanochannel, the research progress in the field of single entities sensing, and the novel sensing strategies on solving the above problems in solid-state nanopore/nanochannel single-entity sensing. At the same time, the challenges and prospects of solid-state nanopore/nanochannel for single-entity electrochemical sensing are also discussed.

An ultrasensitive aptasensor of SARS-CoV-2 N protein based on ion current rectification with nanopipettes

Since the outbreak of COVID-19 in the world, it has spread rapidly all over the world. Rapid and effective detection methods have been a focus of research. The SARS-CoV-2 N protein (NP) detection methods currently in use focus on specific recognition of antibodies, but the reagents are expensive and difficult to be produced. Here, aptamer-functionalized nanopipettes utilize the unique ion current rectification (ICR) of nanopipette to achieve rapid and highly sensitive detection of trace NP, and can significantly reduce the cost of NP detection. In the presence of NP, the surface charge at the tip of the nanopipette changes, which affects ion transport and changes the degree of rectification. Quantitative detection of NP is achieved through quantitative analysis. Relying on the high sensitivity of nanopipettes to charge fluctuations, this sensor platform achieves excellent sensing performance. The sensor platform exhibited a dynamic working range from 10²-10⁶ pg/mL with a detection limit of 73.204 pg/mL, which showed great potential as a tool for rapidly detecting SARS-CoV-2. As parallel and serial testing are widely used in the clinic to avoid missed diagnosis or misdiagnosis, we hope this platform can play a role in controlling the spread and prevention of COVID-19.