The single strand template shortening strategy improves the sensitivity and specificity of solid-state nanopore detection.

Through controlling the ssDNA product length of rolling circle amplification with AcyNTP, here we develop a nanopore signal enhancement strategy (STSS), which can successfully transfer the short oligonucleotide targets into long ssDNAs with appropriate lengths that can generate significant translocation currents. By labelling the RCA product with tags such as tetrahedral structures and isothermal amplicons, the resolution, signal specificity, and target range of the STSS can be further extended.

Nanopore sensitization based on a double loop hybridization chain reaction and G-quadruplex.

The widespread implementation of solid-state nanopores faces challenges such as lower resolution and increased electrical noise when compared to biological nanopores. Incorporating specific nucleic acid reactions can enhance resolution. In this study, we've developed a nucleic acid amplifier to enhance the sensitivity of solid-state nanopores, utilizing a G-rich sequence and hybridization chain reaction. This amplifier improves target concentration and volume amplification, showing promise in nanopore sensitivity tests.

A Duplex Polymerization Strategy for General, Programmable and High-Resolution Nanopore-Based Sensing.

Nanopore sensing is highly promising in single molecular analysis but their broad applications have been challenged by the limited strategies that can transduce a target-of-interest into a specific and anti-false/inference signal, especially for solid-state nanopores with relatively lower resolution and higher noise. Here we report a high-resolution signal-production concept named target-induced duplex polymerization strategy (DPS). Through linking the same or different duplex substrates (DSs) with a special linker (L) and an optional structure tag (ST), the DPS can generate target-specific DS polymers with highly controllable duration times, duration intervals and even distinguished secondary tagging currents. Experimentally, DPS mono-polymerization of single DS and co-polymerization of multiple DSs has verified the duration time of a DPS product is the sum of those for each DS monomer. Tetrahedron-DNA structures with different sizes are used as the STs to provide needle-like secondary peaks for further resolution enhancement and multiplex assay. With these examples DPS represents a general, programmable and advanced strategy that may simultaneously provide size-amplification, concentration amplification, and signal-specificity for molecular recognition. It is also promisingly in various applications regarding to single molecular investigation, such as polymerization degree, structure/side chain conformation, programmable multiplex decoding and information index.

Single Molecular Nanopores as a Label-Free Method for Homogeneous Conformation Investigation and Anti-Interference Molecular Analysis.

In this paper, we propose a "reciprocal strategy" that, on the one hand, explores the ability of solid-state nanopores in a homogeneous high-fidelity characterization of nucleic acid assembly and, on the other hand, the formed nucleic acid assembly with a large size serves as an amplifier to provide a highly distinguished and anti-interference signal for molecular sensing. Four-hairpin hybridization chain reaction (HCR) with G-rich tail tags is taken as the proof-of-concept demonstration. G-rich tail tags are commonly used to form G-quadruplex signal probes on the side chain of HCR duplex concatemers. When such G-tailed HCR concatemers translocate the nanopore, abnormal, much higher nanopore signals over normal duplexes can be observed. Combined with atomic force microscopy, we reveal the G-rich tail may easily induce the "intermolecular interaction" between HCR concatemers to form "branched assembly structure (BAS)". To the best of our knowledge, this is the first evidence for the formation BAS of the G tailed HCR concatemers in a homogeneous solution. Systematic nanopore measurements further suggest the formation of these BASs is closely related to the types of salt ions, the amount of G, the concentration of substrate hairpins, the reaction time, and so forth. Under optimized conditions, these BASs can be grown to just the right size without being too large to block the pores, while producing a current 14 times that of conventional double-stranded chains. Here, these very abnormal large current blockages have, in turn, been taken as an anti-interference signal indicator for small targets in order to defend the high noises resulting from co-existing big species (e.g., enzymes or other long double-stranded DNA).

Lego-Like Catalytic Hairpin Assembly Enables Controllable DNA-Oligomer Formation and Spatiotemporal Amplification in Single Molecular Signaling.

While the solid-state nanopore shows increasing potential during sensitive and label-free single molecular analysis, target concentration and signal amplification method is in urgent need. In this article, a solution via designing a model nucleic acid circuit reaction that can produce "Y" shape-structure three-way DNA oligomers with controllable size and polymerization degree is proposed. Such a so-called lego-like three-way catalytic hairpin assembly (LK-3W-CHA) can provide both concentration amplification (via CHA circuit) and programmable size control (via lego-like building mode) to enhance spatiotemporal resolution in single molecular sensing of solid-state nanopore. Oligomers containing 1-4 DNA three-way junctions (Y monomers, Y1-Y4) are designed in proof-of-concept experiments and applications. When the oligomers are applied to direct translocation measurements, Y2-Y4 can significantly increase the signal resolution and stability than that of Y1. Meanwhile, Y1 to Y4 can be used as the tags on the long DNA carrier to provide very legible secondary signals for specific identification, multiple assays, and information storage. Compared with other possible tags, Y1-Y4 provides higher signal density and amplitude, and quasi-linear "inner reference" for each other, which may provide more systematic, reliable, and controllable experimental results.

Impact of the national hepatitis B immunization program in China: a modeling study.

BACKGROUND: Elimination of hepatitis B virus (HBV) is a striking challenge for countries with high or moderate disease burden. Therefore, using China as a practical case to share experiences for similar countries may accelerate the achievement of the WHO 2030 target of 90% reduction in HBV-related incidence. We aim to evaluate the impact of national HBV immunization strategies in China; and the feasibility to achieve WHO 2030 targets under different scenarios. METHODS: We constructed an expanded Susceptible-Exposed-Infectious-Recovered (SEIR) model and decision tree-Markov model to estimate the epidemic of HBV in China, assess the feasibility of 2030 Elimination Goals through the projections and conduct the economic analysis. Least square method was used to calibrate the expanded SEIR model by yearly data of laboratory-confirmed HBV cases from 1990 to 2018. Two models were separately used to evaluate the impact and cost-effectiveness of HBV vaccine by comparing prevalence of chronic HBV infections, quality-adjusted life-years (QALYs), incremental cost effectiveness ratio and benefit-cost ratio (BCR) under various intervention options, providing a basis for exploring new containment strategies. RESULTS: Between 1990 and 2020, the number of chronic HBV infections decreased by 33.9%. The current status quo would lead to 55.73 million infections (3.95% prevalence) in 2030, compared to 90.63 million (6.42% prevalence) of the "Without the NIP" scenario (NIP: National Immunization Program), 114.78 million (8.13% prevalence) without any interventions. The prevention of mother to child transmission (PMTCT) strategy showed a net benefit as 12,283.50 dollars per person, with BCR as 12.66, which is higher than that of universal vaccination at 9.49. Compared with no screening and no vaccination, the PMTCT strategy could save 7726.03 dollars for each QALY increase. CONCLUSIONS: Our findings proved the HBV vaccination has demonstrated a substantial positive impact on controlling the epidemic of HBV in terms of effectiveness and economy after about 30 years of implementation of the national hepatitis B immunization program which also provided containment experience for high or medium burden countries. As for China, the next step should focus on exploring strategies to improve diagnosis and treatment coverage to reduce the burden of HBV-related deaths and ultimately eliminate HBV.

CircPCBP2 promotes the stemness and chemoresistance of DLBCL via targeting miR-33a/b to disinhibit PD-L1.

Diffuse large B-cell lymphoma (DLBCL) is the most common lymphoid malignancy with a high relapse rate of up to 40%. The prognosis of the disease needs improvement and requires a understanding of its molecular mechanism. We investigated the mechanisms of DLBCL development and its sensitivity to chemotherapy by focusing on circPCBP2/miR-33a/b/PD-L1 axis. Human DLBCL specimens and cultured cancer cell lines were used. Features of circPCBP2 were systematically characterized through Sanger sequencing, Actinomycin D, RNase R treatment, and FISH. The expression levels of circPCBP2, miR-33a/b, PD-L1, stemness-related markers, ERK/AKT and JAK2/STAT3 signaling were measured using qRT-PCR, western blotting, and immunohistochemistry. Stemness of DLBCL cells was assessed through spheroid formation assay and flow cytometry. Cell viability and apoptosis upon cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) treatment were determined using MTT assay and flow cytometry, respectively. Interactions of circPCBP2-miR-33a/b and miR-33a/b-PD-L1 were validated using dual luciferase activity assay and RNA-RIP. Nude mouse xenograft model was used to assess the function of circPCBP2 in DLBCL growth in vivo. circPCBP2 was upregulated in human DLBCL specimens and cultured DLBCL cells while miR-33a/b was reduced. Knockdown of circPCBP2 or miR-33a/b overexpression inhibited the stemness of DLBCL cells and promoted cancer cell apoptosis upon CHOP treatment. circPCBP2 directly bound with miR-33a/b while miR-33a/b targeted PD-L1 3'-UTR. circPCBP2 disinhibited PD-L1 signaling via sponging miR-33a/b. miR-33a/b inhibitor and activating PD-L1 reversed the effects of circPCBP2 knockdown and miR-33a/b mimics, respectively. circPBCP2 knockdown restrained DLBCL growth in vivo and potentiated the anti-tumor effects of CHOP. In conclusion, circPCBP2 enhances DLBCL cell stemness but suppresses its sensitivity to CHOP via sponging miR-33a/b to disinhibit PD-L1 expression. circPCBP2/miR-33a/b/PD-L1 axis could serve as a diagnosis marker or therapeutic target for DLBCL.

Atomic-precision Pt6 nanoclusters for enhanced hydrogen electro-oxidation.

The discord between the insufficient abundance and the excellent electrocatalytic activity of Pt urgently requires its atomic-level engineering for minimal Pt dosage yet maximized electrocatalytic performance. Here we report the design of ultrasmall triphenylphosphine-stabilized Pt6 nanoclusters for electrocatalytic hydrogen oxidation reaction in alkaline solution. Benefiting from the self-optimized ligand effect and atomic-precision structure, the nanocluster electrocatalyst demonstrates a high mass activity, a high stability, and outperforms both Pt single atoms and Pt nanoparticle analogues, uncovering an unexpected size optimization principle for designing Pt electrocatalysts. Moreover, the nanocluster electrocatalyst delivers a high CO-tolerant ability that conventional Pt/C catalyst lacks. Theoretical calculations confirm that the enhanced electrocatalytic performance is attributable to the bifold effects of the triphenylphosphine ligand, which can not only tune the formation of atomically precise platinum nanoclusters, but also shift the d-band center of Pt atoms for favorable adsorption kinetics of *H, *OH, and CO.

Polycyclic Aromatic Hydrocarbons as a New Class of Promising Cathode Materials for Aluminum-Ion Batteries.

As an emerging post-lithium battery technology, aluminum ion batteries (AIBs) have the advantages of large Al reserves and high safety, and have great potential to be applied to power grid energy storage. But current graphite cathode materials are limited in charge storage capacity due to the formation of stage-4 graphite-intercalated compounds (GICs) in the fully charged state. Herein, we propose a new type of cathode materials for AIBs, namely polycyclic aromatic hydrocarbons (PAHs), which resemble graphite in terms of the large conjugated π bond, but do not form GICs in the charge process. Quantum chemistry calculations show that PAHs can bind AlCl4 - through the interaction between the conjugated π bond in the PAHs and AlCl4 - , forming on-plane interactions. The theoretical specific capacity of PAHs is negatively correlated with the number of benzene rings in the PAHs. Then, under the guidance of theoretical calculations, anthracene, a three-ring PAH, was evaluated as a cathode material for AIBs. Electrochemical measurements show that anthracene has a high specific capacity of 157 mAh g-1 (at 100 mA g-1 ) and still maintains a specific capacity of 130 mAh g-1 after 800 cycles. This work provides a feasible "theory guides practice" research model for the development of energy storage materials, and also provides a new class of promising cathode materials for AIBs.

Chitosan and κ-carrageenan-derived nitrogen and sulfur co-doped carbon dots "on-off-on" fluorescent probe for sequential detection of Fe3+ and ascorbic acid.

This study develops a high sensitive and selective "on-off-on" fluorescent probe for sequential detection of iron ion (Fe3+) and ascorbic acid (AA) based on nitrogen and sulfur co-doped carbon dots (N, S-CDs), which were synthesized by using chitosan and κ-carrageenan as raw materials through one-step hydrothermal protocol. The synthesized N,S-CDs possess particularly high quantum yield (QY = 59.31%), excellent stability and excitation dependent behavior, showing great potential for practical applications. Furthermore, N,S-CDs provided high selectivity and strong anti-interference to Fe3+ due to its fluorescence quenching performance, revealing a wide linear concentration range from 1 to 100 µM for the detection of Fe3+ ion with an extremely low limit of detection of 57 nM, and presented reliable and accurate results in actual sample detection of Fe3+. The overall fluorescence quenching mechanism of N,S-CDs with Fe3+ was due to the formation of N,S-CDs/Fe3+ initiated to the aggregation and electron transfer of N,S-CDs, resulting in the static quenching of fluorescence. More interestingly, AA could reduce Fe3+ to Fe2+ and efficaciously recover the quenched fluorescence of N,S-CDs/Fe3+. N,S-CDs/Fe3+ as "turn-on" fluorescent probe was further applied for detecting AA in a linear range of 0.5-90 µM with a detection limit of 38 nM.

Impact of immunization programs on 11 childhood vaccine-preventable diseases in China: 1950-2018.

To evaluate the achievements of China's immunization program between 1950 and 2018, we chose 11 vaccine-preventable diseases (VPDs) as representative notifiable diseases and used annual surveillance data obtained between 1950 and 2018 to derive disease incidence and mortality trends. Quasi-Poisson and polynomial regression models were used to estimate the impacts of specific vaccine programs, and life-table methods were used to calculate the loss of life expectancy, years of life lost, and loss of working years. The total notification number for the 11 VPDs was 211,866,000 from 1950 to 2018. The greatest number occurred in 1959, with a total incidence of 1,723 per million persons. From 1978 to 2018, a substantial decline was observed in the incidence of major infectious diseases. The incidence of pertussis fell 98% from 126.35 to 1.58 per million, and the incidences of measles, meningococcal meningitis, and Japanese encephalitis fell 99%, 99%, and 98%, respectively. The regression models showed that most of the 11 diseases exhibited dramatic declines in morbidity after their integration into the Expanded Program on Immunization (EPI), while varicella and paratyphoid fever, which were not integrated into the EPI, showed increased morbidity. From 1978 to 2018, the total life expectancy for the 11 VPDs increased by 0.79 years, and similar results were obtained for different age groups. China has had great success in controlling VPDs in recent decades, and improving vaccination coverage is a key aspect of controlling VPDs in China.

miR-486 Promotes the Invasion and Cell Cycle Progression of Ovarian Cancer Cells by Targeting CADM1.

OBJECTIVE: To explore the role and possible underlying mechanism of miR-486 in ovarian cancer (OC) cells. METHODS: The expression of miR-486 and CADM1 was detected by qRT-PCR in OC tissues and adjacent nontumor tissues and OC cell lines. The dual-luciferase reporter gene system was used to determine the targeting relationship between miR-486 and CADM1. CCK-8, colony formation assay, Transwell, and flow cytometry were performed to detect cell proliferation, cell invasion, cell cycle progression, and the apoptotic cell death, respectively. Western blot was carried out to detect the expression of CADM1 protein and the proteins associated with cell cycle progression. RESULTS: miR-486 was significantly upregulated in OC tissues and cells, while CADM1 expression was significantly downregulated. Dual-luciferase reporter assays further confirmed that CADM1 was a target gene of miR-486. Interference with miR-486 could inhibit the proliferation and invasion and promoted the apoptosis of SKOV3 cells. Knocking down both miR-486 and CADM1 significantly increased the SKOV3 cell proliferation, invasion, and the number of cells transitioning from the G0/G1 phase into the S phase of cell cycle and reduced the cellular apoptosis. Western blot analysis revealed that the expression of cell cycle progression-related proteins (CyclinD1, CyclinE, and CDK6) was significantly reduced, and the p21 expression was increased when interfering with both miR-486 and CADM1 expression. CONCLUSION: Our results suggested that miR-486 could act as a tumor promoter by targeting CADM1 and be a potential therapeutic target for the treatment of OC.

Changes in newly notified cases and control of tuberculosis in China: time-series analysis of surveillance data.

BACKGROUND: China has made progress in tuberculosis control, but this disease remains a burden in many regions of China. We performed time-series analysis to examine changes in the rates of newly notified and newly smear-positive cases of tuberculosis in different regions of China from 1997 to 2018 and assessed the effect of the current control program. METHODS: National and provincial notification data on tuberculosis from 1997 to 2018, which covers 31 provinces in the mainland of China, were extracted from the Chinese public health science data center. The annual percentage changes in newly notified and smear-positive cases were analyzed using a joinpoint regression method. RESULTS: There were 18 646 672 newly notified tuberculosis cases from 1997 to 2018, with the greatest number in 2005. A total of 6 605 414 of these cases (35.42%) were smear-positive cases. The number of newly notified cases in China overall decreased (96.88-59.27 cases per 100 000) significantly during the most recent years. The decline during this period ranged from -3.9% (95% CI -5.7 to -2.9) in the western region to -4.3% (95% CI -4.8 to -3.7) in the eastern region. Most provinces had significant declines in newly notified and smear-positive cases, whereas the decline of newly smear-positive cases in Xinjiang was about half of that observed during the same period in China overall (-4.1% vs -9.9%). In addition to disparities in annual percentage changes, the rate of newly notified cases was higher in the western region than in the eastern and central regions. CONCLUSIONS: The burden of tuberculosis has been on declining throughout China during recent years, but tuberculosis in western China continues to be a public health emergency that needs to be urgently addressed. Effective prevention and control strategies are needed for regions with high disease burdens and those with increasing or unchanging numbers of newly notified and smear-positive cases of tuberculosis.

Gap to End-TB targets in eastern China: A joinpoint analysis from population-based notification data in Zhejiang Province, China, 2005-2018.

BACKGROUND: Zhejiang is a southeastern province of China with middle level notification rates of tuberculosis in China, but more than 27,000 pulmonary tuberculosis (PTB) cases are still reported annually in this province. We aimed to analyze the time trends of PTB cases and bacteriologically confirmed cases notification rates at the province and city levels of Zhejiang during 2005-2018. METHODS: Data from the web-based TB Information Management System of Zhejiang Province were used to calculate annual notification rates per 100,000 population of PTB cases and bacteriologically confirmed cases for Zhejiang Province and its 11 cities. The joinpoint regression method was used to analyze the time trends and calculate the annual percentage change of notification rates. RESULTS: There were 480,668 notified PTB cases in Zhejiang Province during 2005-2018, 38.78% of which were bacteriologically confirmed cases. Both the PTB cases and bacteriologically confirmed cases notification rates of Zhejiang Province have declined since 2007. Most of the cities' time trends were the same as Zhejiang Province. The PTB cases and bacteriologically confirmed cases notification rates of males and elderly people are the highest in both sexes and among the four age groups, but the decline speeds of the two groups were slowest. CONCLUSIONS: With the effective implementation of TB control measures and projects, the PTB cases notification rates of Zhejiang Province have declined. In order to reach the target in 2035 of the End TB Strategy, additional efforts should be made in the diagnosis and treatment of TB patients, particularly with regard to males and older adult people.

Chitosan-derived N-doped carbon dots for fluorescent determination of nitrite and bacteria imaging.

N-doped carbon dots (N-CDs) were successfully synthesized via simple one-step hydrothermal carbonization using chitosan as carbon and nitrogen sources. The obtained N-CDs contained a variety of functional groups on the NCDs surface, and exhibited excitation-independent behavior and strong blue fluorescence with a relatively higher fluorescence quantum yield (QY = 35%). It also presented excellent water solubility, resistance to pH change, high ion strength and UV irradiation. Since the fluorescence of the N-CDs could be selectively quenched by NO2-, they could act as a fluorescent sensor for the determination of NO2- in real tap water and lake water samples with a wide linear range (1-500 µM) and low detection limit (0.1 µM). They could also be used for bacterial imaging as multicolor fluorescent probes. The results indicated that N-CDs could be a promising candidate material for biomedical applications.

Low-Noise Solid-State Nanopore Enhancing Direct Label-Free Analysis for Small Dimensional Assemblies Induced by Specific Molecular Binding.

Solid-state nanopores show special potential as a new single-molecular characterization for nucleic acid assemblies and molecular machines. However, direct recognition of small dimensional species is still quite difficult due the lower resolution compared with biological pores. We recently reported a very efficient noise-reduction and resolution-enhancement mechanism via introducing high-dielectric additives (e.g., formamide) into conical glass nanopore (CGN) test buffer. Based on this advance, here, for the first time, we apply a bare CGN to directly recognize small dimensional assemblies induced by small molecules. Cocaine and its split aptamer (Capt assembly) are chosen as the model set. By introducing 20% formamide into CGN test buffer, high cocaine-specific distinguishing of the 113 nt Capt assembly has been realized without any covalent label or additional signaling strategies. The signal-to-background discrimination is much enhanced compared with control characterizations such as gel electrophoresis and fluorescence resonance energy transfer (FRET). As a further innovation, we verify that low-noise CGN can also enhance the resolution of small conformational/size changes happening on the side chain of large dimensional substrates. Long duplex concatamers generated from the hybridization chain reaction (HCR) are selected as the model substrates. In the presence of cocaine, low-noise CGN has sensitively captured the current changes when the 26 nt aptamer segment is assembled on the side chain of HCR duplexes. This paper proves that the introduction of the low-noise mechanism has significantly improved the resolution of the solid-state nanopore at smaller and finer scales and thus may direct extensive and deeper research in the field of CGN-based analysis at both single-molecular and statistical levels, such as molecular recognition, assembly characterization, structure identification, information storage, and target index.

Study on the Functionalization and Signaling Efficiency of the Hybridization Chain Reaction Using Traditional and Single Molecular Characterizations.

As an important enzyme-free amplifier, the hybridization chain reaction (HCR) uses an ssDNA to trigger cycled displacement interactions between substrate hairpins and finally form elongated dsDNA concatamer mixtures. In many cases, to provide a signal probe or advanced function, additional oligonucleotides (named hairpin tails) have to be extended upon classic HCR hairpin substrates, but by doing so the HCR assembly efficiency and signal-to-noise ratio (SNR) may get seriously reduced. In this Article, a rational and general model that may guide the study on HCR functionalization and signaling efficiency is provided. We rationally design a four-hairpin model HCR system (4H-HCR) in which one or more hairpin substrates are appended with additional tails as a signaling probe. After HCR assembly, two adjacent tails are supposedly integrating into a full G-quadruplex structure to provide the evidence or signal for the assembly. A systematic study has been applied to reveal the relationship between the "tail-design" with assembly efficiency and SNR. A clear design rule-set guiding the optimized assembly and signal has been provided for traditional electrophoresis and G-quadruplex-enhanced fluorescence signal. Importantly, solid-state nanopore single molecular detection has been innovatively introduced and recommended as an "antirisk" and "mutual benefit" readout to traditional G-quadruplex signaling. Nanopore detection can provide a clear signal distinguished before and after the HCR reaction, especially when the traditional G-quadruplex-enhanced signal only provides low SNR. The G-quadruplex, in turn, may enhance the nanopore signal amplitude via increasing the diameter of the HCR products.

Corrigendum to "miR-486 Promotes the Invasion and Cell Cycle Progression of Ovarian Cancer Cells by Targeting CADM1".

[This corrects the article DOI: 10.1155/2021/7407086.].

Risk assessment and evaluation of China's policy to prevent COVID-19 cases imported by plane.

As of October 5, 2020, China has reported 2,921 cases imported from overseas. Assessing the effectiveness of China's current policies on imported cases abroad is very important for China and other countries that are facing or will face overseas imported cases. In April, we used a susceptible-exposed-infectious-recovered metapopulation model to simulate the epidemic in seven foreign countries, China and the three Chinese key cities. Based on the model outside China, we estimated the proportion of people in incubation period and calculated the risk indexes for Chinese cities through analyzing aviation traffic data from these countries. Based on the model in China and the three key cities, we collected information on control measures and quantified the effectiveness of implementing the current policies at different times and intensities. Our model results showed that Shanghai, Beijing, Qingdao, Guangzhou, and Tianjin have the top five risk indexes. As of April 20, 2020, under current measures, the number of confirmed cases could be reduced by 99% compared with no air traffic restrictions and isolation measures; the reduction could be 93% with isolation of passengers only from key countries. If the current policy were postponed for 7, 10, or 20 days, the increase in the number of confirmed cases would be 1,329, 5,524, and 779,245 respectively, which is 2.1, 5.7, and 662.9 times the number of confirmed cases under current measures. Our research indicates that the importation control measures currently taken by China were implemented at an appropriate time to prevent the epidemic spreading and have achieved relatively good control results. However, it is necessary to remain vigilant; otherwise, another outbreak peak could occur.

Low-Noise Nanopore Enables In-Situ and Label-Free Tracking of a Trigger-Induced DNA Molecular Machine at the Single-Molecular Level.

Solid-state nanopores have shown special high potential in a label-free molecular assay, structure identification, and target-index at the single-molecular level, even though frustrating electrical baseline noise is still one of the major factors that limit the spatial resolution and signaling reliability of solid-state nanopores, especially in small target detection. Here we develop a significant and easy-operating noise-reduction approach via mixing organic solvents with high dielectric constants into a traditional aqueous electrolyte. The strategy is generally effective for pores made of different materials, such as the most commonly used conical glass (CGN) or SiNx. While the mechanism should be multisourced, MD simulations suggest the noise reduction may partially arise from the even ionic distribution caused by the addition of higher dielectric species. Among all solvents experimentally tested, the two with the highest dielectric constants, formamide and methylformamide, exhibit the best noise reduction effect for target detection of CGN. The power spectral density at the low-frequency limit is reduced by nearly 3 orders with the addition of 20% formamide. Our work qualifies the reliability of solid-state nanopores into much subtler scales of detection, such as dsDNAs under 100 bp. As a practical example, bare CGN is innovatively employed to perform in-situ tracking of trigger-responsive DNA machine forming oligomers.