Slowing DNA translocation through a nanopore using a functionalized electrode

Recent advances of nanopore technique in single cell analysis

Single cells and their dynamic behavior are closely related to biological research. Monitoring their dynamic behavior is of great significance for disease prevention. How to achieve rapid and non-destructive monitoring of single cells is a major issue that needs to be solved urgently. As an emerging technology, nanopores have been proven to enable non-destructive and label-free detection of single cells. The structural properties of nanopores enable a high degree of sensitivity and accuracy during analysis. In this article, we summarize and classify the different types of solid-state nanopores that can be used for single-cell detection and illustrate their specific applications depending on the size of the analyte. In addition, their research progress in material transport and microenvironment monitoring is also highlighted. Finally, a brief summary of existing research challenges and future trends in nanopore single-cell analysis is tentatively provided.

Formation of Molecular Junctions by Single-Entity Collision Electrochemistry

Controlling and understanding the chemistry of molecular junctions is one of the major themes in various fields ranging from chemistry and nanotechnology to biotechnology and biology. Stochastic single-entity collision electrochemistry (SECE) provides powerful tools to study a single entity, such as single cells, single particles, and even single molecules, in a nanoconfined space. Molecular junctions formed by SECE collision show various potential applications in monitoring molecular dynamics with high spatial resolution and high temporal resolution and in feasible combination with hybrid techniques. This Perspective highlights the new breakthroughs, seminal studies, and trends in the area that have been most recently reported. In addition, future challenges for the study of molecular junction dynamics with SECE are discussed.

Nanopores in Graphene and Other 2D Materials: A Decade's Journey toward Sequencing

Nanopore techniques offer a low-cost, label-free, and high-throughput platform that could be used in single-molecule biosensing and in particular DNA sequencing. Since 2010, graphene and other two-dimensional (2D) materials have attracted considerable attention as membranes for producing nanopore devices, owing to their subnanometer thickness that can in theory provide the highest possible spatial resolution of detection. Moreover, 2D materials can be electrically conductive, which potentially enables alternative measurement schemes relying on the transverse current across the membrane material itself and thereby extends the technical capability of traditional ionic current-based nanopore devices. In this review, we discuss key advances in experimental and computational research into DNA sensing with nanopores built from 2D materials, focusing on both the ionic current and transverse current measurement schemes. Challenges associated with the development of 2D material nanopores toward DNA sequencing are further analyzed, concentrating on lowering the noise levels, slowing down DNA translocation, and inhibiting DNA fluctuations inside the pores. Finally, we overview future directions of research that may expedite the emergence of proof-of-concept DNA sequencing with 2D material nanopores.

Nanopore sensing: A physical-chemical approach

Protein nanopores have emerged as an important class of sensors for the understanding of biophysical processes, such as molecular transport across membranes, and for the detection and characterization of biopolymers. Here, we trace the development of these sensors from the Coulter counter and squid axon studies to the modern applications including exquisite detection of small volume changes and molecular reactions at the single molecule (or reactant) scale. This review focuses on the chemistry of biological pores, and how that influences the physical chemistry of molecular detection.

Nanodiagnostics: A review of the medical capabilities of nanopores

Modern diagnostics strive to be accurate, fast, and inexpensive in addition to properly identifying the presence of a disease, infection, or illness. Early diagnosis is key; catching a disease in its early stages can be the difference between fatality and treatment. The challenge with many diseases is that detectability of the disease scales with disease progression. Since single molecule sensors, e.g., nanopores, can sense biomolecules at low concentrations, they have the potential to become clinically relevant in many of today's medical settings. With nanopore-based sensing, lower volumes and concentrations are required for detection, enabling it to be clinically beneficial. Other advantages to using nanopores include that they are tunable to an enormous variety of molecules and boast low costs, and fabrication is scalable for manufacturing. We discuss previous reports and the potential for incorporating nanopores into the medical field for early diagnostics, therapeutic monitoring, and identifying relapse/recurrence.

On Stochastic Reduction in Laser-Assisted Dielectric Breakdown for Programmable Nanopore Fabrication

The controlled dielectric breakdown emerged as a promising alternative toward accessible solid-state nanopore fabrication. Several prior studies have shown that laser-assisted dielectric breakdown could help control the nanopore position and reduce the possibility of forming multiple pores. Here, we developed a physical model to estimate the probability of forming a single nanopore under different combinations of the laser power and the electric field. This model relies on the material- and experiment-specific parameters: the Weibull statistical parameters and the laser-induced photothermal etching rate. Both the model and our experimental data suggest that a combination of a high laser power and a low electric field is statistically favorable for forming a single nanopore at a programmed location. While this model relies on experiment-specific parameters, we anticipate it could provide the experimental insights for nanopore fabrication by the laser-assisted dielectric breakdown method, enabling broader access to solid-state nanopores and their sensing applications.

Wafer-level fabrication of individual solid-state nanopores for sensing single DNAs

For biomolecule sensing purposes a solid-state nanopore platform based on silicon has certain advantages as compared to nanopores on other substrates such as graphene, silicon nitride, silicon oxide etc Capitalizing on the developed CMOS technology, nanopores on silicon are scalable without any requirement for additional processing, the devices are low cost and the process can be repeatable with a high yield. One of the essential requirements in biomolecule sensing is the ability of the nanopore to interact with the analyte. In this work, we present a method for processing high aspect ratio, single nanopores in the range of 10-30 nm in diameter and approximately 700 nm in length on a silicon-on-insulator (SOI) wafer. The presented method of manufacturing the high aspect ratio individual nanopores combines optical lithography and anisotropic KOH etching with a final electrochemical etching step to form the nanopores and is repeatable and can be processed in batches. We demonstrate electrical detection of dsDNA translocation, where the characteristic time of the process is in the millisecond range. We also analyse the translocation parameters and correlate the enhanced length of the nanopore to a longer translocation time as compared to other substrates.

Tailoring Dielectric Surface Charge via Atomic Layer Thickness

Channel surface property is a crucial factor that affects capture-to-translocation dynamics of single-particles in solid-state pores. Here, we show that atomically-thin dielectrics can be used to finely tune the pore wall surface potential. We isotopically coated alumina of atomically controlled thickness on a Si₃N₄ micropore. The surface zeta-potential in a buffer was found to decrease sharply by 1 nm thick deposition that served as a water-permeable ultra-thin sheet to modulate the effective charge density of the Al₂O₃/Si₃N₄ multilayer structure. Further thickening of the atomic layer enabled to control the zeta potential with a thickness at 3.4 mV/nm resolution. Accordingly, we observed concomitant enhancement in the capture rate and the translocation speed of negatively charged polymeric particles by virtue of the mitigated electroosmotic back flow in the functionalized pore channel. This simple method is widely applicable for tailoring the surface charge properties of essentially any sensors and devices working in aqueous media.

Highly Conductive Nucleotide Analogue Facilitates Base-Calling in Quantum-Tunneling-Based DNA Sequencing

Quantum-tunneling-based DNA sequencing is a single molecular technology that has great potential for achieving facile and high-throughput DNA sequencing. In principle, the sequence of DNA could be read out by the time trace of the tunnel current that can be changed according to molecular conductance of nucleobases passing through nanosized gap electrodes. However, efficient base-calling of four genetic alphabets has been seriously impeded due to the similarity of molecular conductance among canonical nucleotides. In this article, we demonstrate that replacement of canonical 2'-deoxyadenosine (dA) with a highly conductive dA analogue, 7-deaza dA, could expand the difference of molecular conductance between four genetic alphabets. Additionally, systematic evaluation of molecular conductance using a series of dA and dG analogues revealed that molecular conductance of the nucleotide is highly dependent on the HOMO level. Thus, the present study demonstrating that signal characteristics of the nucleotide can be modulated based on the HOMO level provides a widely applicable chemical approach and insight for facilitation of single molecular sensing as well as DNA sequencing based on quantum tunneling.

Selective detections of single-viruses using solid-state nanopores

Rapid diagnosis of flu before symptom onsets can revolutionize our health through diminishing a risk for serious complication as well as preventing infectious disease outbreak. Sensor sensitivity and selectivity are key to accomplish this goal as the number of virus is quite small at the early stage of infection. Here we report on label-free electrical diagnostics of influenza based on nanopore analytics that distinguishes individual virions by their distinct physical features. We accomplish selective resistive-pulse sensing of single flu virus having negative surface charges in a physiological media by exploiting electroosmotic flow to filter contaminants at the Si₃N₄ pore orifice. We demonstrate identifications of allotypes with 68% accuracy at the single-virus level via pattern classifications of the ionic current signatures. We also show that this discriminability becomes >95% under a binomial distribution theorem by ensembling the pulse data of >20 virions. This simple mechanism is versatile for point-of-care tests of a wide range of flu types.

Recent Progress in Solid-State Nanopores

The solid-state nanopore has attracted much attention as a next-generation DNA sequencing tool or a single-molecule biosensor platform with its high sensitivity of biomolecule detection. The platform has advantages of processability, robustness of the device, and flexibility in the nanopore dimensions as compared with the protein nanopore, but with the limitation of insufficient spatial and temporal resolution to be utilized in DNA sequencing. Here, the fundamental principles of the solid-state nanopore are summarized to illustrate the novelty of the device, and improvements in the performance of the platform in terms of device fabrication are explained. The efforts to reduce the electrical noise of solid-state nanopore devices, and thus to enhance the sensitivity of detection, are presented along with detailed descriptions of the noise properties of the solid-state nanopore. Applications of 2D materials including graphene, h-BN, and MoS₂ as a nanopore membrane to enhance the spatial resolution of nanopore detection, and organic coatings on the nanopore membranes for the addition of chemical functionality to the nanopore are summarized. Finally, the recently reported applications of the solid-state nanopore are categorized and described according to the target biomolecules: DNA-bound proteins, modified DNA structures, proteins, and protein oligomers.

Nitrogen Doping of Carbon Nanoelectrodes for Enhanced Control of DNA Translocation Dynamics

Controlling the dynamics of DNA translocation is a central issue in the emerging nanopore-based DNA sequencing. To address the potential of heteroatom doping of carbon nanostructures and for achieving this goal, herein, we carry out atomistic molecular dynamics simulations for single-stranded DNAs translocating between two pristine or doped carbon nanotube (CNT) electrodes. Specifically, we consider the substitutional nitrogen doping of capped CNT (capCNT) electrodes and perform two types of molecular dynamics simulations for the entrapped and translocating single-stranded DNAs. We find that the substitutional nitrogen doping of capCNTs facilitates and stabilizes the edge-on nucleobase configurations rather than the original face-on ones and slows down the DNA translocation speed by establishing hydrogen bonds between the N dopant atoms and nucleobases. Due to the enhanced interactions between DNAs and N-doped capCNTs, the duration time of nucleobases within the nanogap was extended by up to ∼300%. Given the possibility to be combined with the extrinsic light or gate voltage modulation methods, the current work demonstrates that the substitutional nitrogen doping is a promising direction for the control of DNA translocation dynamics through a nanopore or nanogap, based of carbon nanomaterials.

Identification of Individual Bacterial Cells through the Intermolecular Interactions with Peptide-Functionalized Solid-State Pores

Bioinspired pore sensing for selective detection of flagellated bacteria was investigated. The Au micropore wall surface was modified with a synthetic peptide designed from toll-like receptor 5 (TLR5) to mimic the pathogen-recognition capability. We found that intermolecular interactions between the TLR5-derived recognition peptides and flagella induce ligand-specific perturbations in the translocation dynamics of Escherichia coli, which facilitated the discrimination between the wild-type and flagellin-deletion mutant (ΔfliC) by the resistive pulse patterns thereby demonstrating the sensing of bacteria at a single-cell level. These results provide a novel concept of utilizing weak intermolecular interactions as a recognition probes for single-cell microbial identification.

Enhancing the sensitivity of DNA detection by structurally modified solid-state nanopore

Solid-state nanopore is an ionic current-based biosensing platform, which would be a top candidate for next-generation DNA sequencing and a high-throughput drug-screening tool at single-molecular-scale resolution. There have been several approaches to enhance the sensitivity and reliability of biomolecule detection using the nanopores particularly in two aspects: signal-to-noise ratio (SNR) and translocation dwell time. In this study, an additional nano-well of 100-150 nm diameter and the aspect ratio of ∼5 called 'guide structure' was inserted in conventional silicon-substrate nanopore device to increase both SNR and dwell time. First, the magnitude of signals (conductance drop (ΔG)) increased 2.5 times under applied voltage of 300 mV through the guide-inserted nanopore compared to the conventional SiN/Si nanopore in the same condition. Finite element simulation was conducted to figure out the origin of ΔG modification, which showed that the guide structure produced high ΔG due to the compartmental limitation of ion transports through the guide to the sensing nanopore. Second, the translocation velocity decreased in the guide-inserted structure to a maximum of 20% of the velocity in the conventional device at 300 mV. Electroosmotic drag formed inside the guide structure, when directly applied to the remaining segment of translocating DNA molecules in cis chamber, affected the DNA translocation velocity. This study is the first experimental report on the effect of the geometrical confinement to a remnant DNA on both SNR and dwell time of nanopore translocations.

Real-time visualization and sub-diffraction limit localization of nanometer-scale pore formation by dielectric breakdown

Herein, we introduce synchronous, real-time, electro-optical monitoring of nanopore formation by DB. Using the same principle as sub-diffraction microscopy, our nanopore localization platform based on wide-field microscopy and calcium indicators provides nanoscale sensitivity. This enables us to establish critical limitations of the fabrication process and improve its reliability. In particular, we find that under certain conditions, multiple nanopores may form and that nanopores may preferentially localize at the membrane junction, either of which potentially render nanopore sensing ineffective. As the breakdown parameters of silicon materials are highly manufacturer-specific, we anticipate that our visualization platform will enable users to easily optimize DB fabrication according to specific needs. Furthermore, our technique furthers the applicability of DB to more complicated architectures, such as membranes with selectively thinned regions and plasmonic nanowells.

Solid-state nanopore localization by controlled breakdown of selectively thinned membranes

We demonstrate precise positioning of nanopores fabricated by controlled breakdown (CBD) on solid-state membranes by spatially varying the electric field strength with localized membrane thinning. We show 100 × 100 nm² precision in standard SiN _x membranes (30-100 nm thick) after selective thinning by as little as 25% with a helium ion beam. Control over nanopore position is achieved through the strong dependence of the electric field-driven CBD mechanism on membrane thickness. Confinement of pore formation to the thinned region of the membrane is confirmed by TEM imaging and by analysis of DNA translocations. These results enhance the functionality of CBD as a fabrication approach and enable the production of advanced nanopore devices for single-molecule sensing applications.

DNA Origami-Graphene Hybrid Nanopore for DNA Detection

DNA origami nanostructures can be used to functionalize solid-state nanopores for single molecule studies. In this study, we characterized a nanopore in a DNA origami-graphene heterostructure for DNA detection. The DNA origami nanopore is functionalized with a specific nucleotide type at the edge of the pore. Using extensive molecular dynamics (MD) simulations, we computed and analyzed the ionic conductivity of nanopores in heterostructures carpeted with one or two layers of DNA origami on graphene. We demonstrate that a nanopore in DNA origami-graphene gives rise to distinguishable dwell times for the four DNA base types, whereas for a nanopore in bare graphene, the dwell time is almost the same for all types of bases. The specific interactions (hydrogen bonds) between DNA origami and the translocating DNA strand yield different residence times and ionic currents. We also conclude that the speed of DNA translocation decreases due to the friction between the dangling bases at the pore mouth and the sequencing DNA strands.

Nanopore Sensing in Aqueous Two-Phase System: Simultaneous Enhancement of Signal and Translocation Time via Conformal Coating

Nanofluidic resistive pulse sensing (RPS) has been extensively used to measure the size, concentration, and surface charge of nanoparticles in electrically conducting solutions. Although various methods have been explored for improving detection performances, intrinsic problems including the extremely low particle-to-pore volume ratio (<0.01%) and fast nanoparticle translocation (10-1000 µs) still induce difficulties in detection, such as low signal magnitudes and short translocation times. Herein, we present an aqueous two-phase system (ATPS) in a nanofluidic RPS for amplifying translocation signals and decreasing translocation speeds simultaneously. Two immiscible aqueous liquids build a liquid-liquid interface inside nanopores. As particles translocate from a high-affinity liquid phase into a lower-affinity one, the high-affinity liquid forms a conformal coating on the particles, which increases the effective particle size and amplifies the current-blockage signal. The translocation time is also increased, as the ATPS interface impedes the particle translocation. For 20 nm particles, 7.92-fold and 5.82-fold enhancements of signal magnitude and translocation time can be achieved. To our knowledge, this is the first attempt to improve nanofluidic RPS by treating an interface of solution reservoirs for manipulating target particles rather than nanopores. This direct particle manipulation allows us to solve the two intrinsic problems all at once.

Simultaneous Ionic Current and Potential Detection of Nanoparticles by a Multifunctional Nanopipette

Nanopore sensing-based technologies have made significant progress for single molecule and single nanoparticle detection and analysis. In recent years, multimode sensing by multifunctional nanopores shows the potential to greatly improve the sensitivity and selectivity of traditional resistive-pulse sensing methods. In this paper, we showed that two label-free electric sensing modes could work cooperatively to detect the motion of 40 nm diameter spherical gold nanoparticles (GNPs) in solution by a multifunctional nanopipette. The multifunctional nanopipettes containing both nanopore and nanoelectrode (pyrolytic carbon) at the tip were fabricated quickly and cheaply. We demonstrated that the ionic current and local electrical potential changes could be detected simultaneously during the translocation of individual GNPs. We also showed that the nanopore/CNE tip geometry enabled the CNE not only to detect the translocation of single GNP but also to collectively detect several GNPs outside the nanopore entrance. The dynamic accumulation of GNPs near the nanopore entrance resulted in no detectable current changes, but was detected by the potential changes at the CNE. We revealed the motions of GNPs both outside and inside the nanopore, individually and collectively, with the combination of ionic current and potential measurements.

Graphene nanodevices for DNA sequencing

Fast, cheap, and reliable DNA sequencing could be one of the most disruptive innovations of this decade, as it will pave the way for personalized medicine. In pursuit of such technology, a variety of nanotechnology-based approaches have been explored and established, including sequencing with nanopores. Owing to its unique structure and properties, graphene provides interesting opportunities for the development of a new sequencing technology. In recent years, a wide range of creative ideas for graphene sequencers have been theoretically proposed and the first experimental demonstrations have begun to appear. Here, we review the different approaches to using graphene nanodevices for DNA sequencing, which involve DNA passing through graphene nanopores, nanogaps, and nanoribbons, and the physisorption of DNA on graphene nanostructures. We discuss the advantages and problems of each of these key techniques, and provide a perspective on the use of graphene in future DNA sequencing technology.

Click Addition of a DNA Thread to the N-Termini of Peptides for Their Translocation through Solid-State Nanopores

Foremost among the challenges facing single molecule sequencing of proteins by nanopores is the lack of a universal method for driving proteins or peptides into nanopores. In contrast to nucleic acids, the backbones of which are uniformly negatively charged nucleotides, proteins carry positive, negative and neutral side chains that are randomly distributed. Recombinant proteins carrying a negatively charged oligonucleotide or polypeptide at the C-termini can be translocated through a α-hemolysin (α-HL) nanopore, but the required genetic engineering limits the generality of these approaches. In this present study, we have developed a chemical approach for addition of a charged oligomer to peptides so that they can be translocated through nanopores. As an example, an oligonucleotide PolyT20 was tethered to peptides through first selectively functionalizing their N-termini with azide followed by a click reaction. The data show that the peptide-PolyT20 conjugates translocated through nanopores, whereas the unmodified peptides did not. Surprisingly, the conjugates with their peptides tethered at the 5'-end of PolyT20 passed the nanopores more rapidly than the PolyT20 alone. The PolyT20 also yielded a wider distribution of blockade currents. The same broad distribution was found for a conjugate with its peptide tethered at the 3'-end of PolyT20, suggesting that the larger blockades (and longer translocation times) are associated with events in which the 5'-end of the PolyT20 enters the pore first.

Gel mesh as "brake" to slow down DNA translocation through solid-state nanopores

Agarose gel is introduced onto the cis side of silicon nitride nanopores by a simple and low-cost method to slow down the speed of DNA translocation. DNA translocation speed is slowed by roughly an order of magnitude without losing signal to noise ratio for different DNA lengths and applied voltages in gel-meshed nanopores. The existence of the gel moves the center-of-mass position of the DNA conformation further from the nanopore center, contributing to the observed slowing of translocation speed. A reduced velocity fluctuation is also noted, which is beneficial for further applications of gel-meshed nanopores. The reptation model is considered in simulation and agrees well with the experimental results.

Interfacing solid-state nanopores with gel media to slow DNA translocations

We demonstrate the ability to slow DNA translocations through solid-state nanopores by interfacing the trans side of the membrane with gel media. In this work, we focus on two reptation regimes: when the DNA molecule is flexible on the length scale of a gel pore, and when the DNA behaves as persistent segments in tight gel pores. The first regime is investigated using agarose gels, which produce a very wide distribution of translocation times for 5 kbp dsDNA fragments, spanning over three orders of magnitude. The second regime is attained with polyacrylamide gels, which can maintain a tight spread and produce a shift in the distribution of the translocation times by an order of magnitude for 100 bp dsDNA fragments, if intermolecular crowding on the trans side is avoided. While previous approaches have proven successful at slowing DNA passage, they have generally been detrimental to the S/N, capture rate, or experimental simplicity. These results establish that by controlling the regime of DNA movement exiting a nanopore interfaced with a gel medium, it is possible to address the issue of rapid biomolecule translocations through nanopores-presently one of the largest hurdles facing nanopore-based analysis-without affecting the signal quality or capture efficiency.

Physical model for recognition tunneling

Recognition tunneling (RT) identifies target molecules trapped between tunneling electrodes functionalized with recognition molecules that serve as specific chemical linkages between the metal electrodes and the trapped target molecule. Possible applications include single molecule DNA and protein sequencing. This paper addresses several fundamental aspects of RT by multiscale theory, applying both all-atom and coarse-grained DNA models: (1) we show that the magnitude of the observed currents are consistent with the results of non-equilibrium Green's function calculations carried out on a solvated all-atom model. (2) Brownian fluctuations in hydrogen bond-lengths lead to current spikes that are similar to what is observed experimentally. (3) The frequency characteristics of these fluctuations can be used to identify the trapped molecules with a machine-learning algorithm, giving a theoretical underpinning to this new method of identifying single molecule signals.

Slowing DNA Transport Using Graphene-DNA Interactions

Slowing down DNA translocation speed in a nanopore is essential to ensuring reliable resolution of individual bases. Thin membrane materials enhance spatial resolution but simultaneously reduce the temporal resolution as the molecules translocate far too quickly. In this study, the effect of exposed graphene layers on the transport dynamics of both single (ssDNA) and double-stranded DNA (dsDNA) through nanopores is examined. Nanopore devices with various combinations of graphene and Al2O3 dielectric layers in stacked membrane structures are fabricated. Slow translocations of ssDNA in nanopores drilled in membranes with layers of graphene are reported. The increased hydrophobic interactions between the ssDNA and the graphene layers could explain this phenomenon. Further confirmation of the hydrophobic origins of these interactions is obtained through reporting significantly faster translocations of dsDNA through these graphene layered membranes. Molecular dynamics simulations confirm the preferential interactions of DNA with the graphene layers as compared to the dielectric layer verifying the experimental findings. Based on our findings, we propose that the integration of multiple stacked graphene layers could slow down DNA enough to enable the identification of nucleobases.

The evolution of nanopore sequencing

The "$1000 Genome" project has been drawing increasing attention since its launch a decade ago. Nanopore sequencing, the third-generation, is believed to be one of the most promising sequencing technologies to reach four gold standards set for the "$1000 Genome" while the second-generation sequencing technologies are bringing about a revolution in life sciences, particularly in genome sequencing-based personalized medicine. Both of protein and solid-state nanopores have been extensively investigated for a series of issues, from detection of ionic current blockage to field-effect-transistor (FET) sensors. A newly released protein nanopore sequencer has shown encouraging potential that nanopore sequencing will ultimately fulfill the gold standards. In this review, we address advances, challenges, and possible solutions of nanopore sequencing according to these standards.

Label-free optical detection of biomolecular translocation through nanopore arrays

In recent years, nanopores have emerged as exceptionally promising single-molecule sensors due to their ability to detect biomolecules at subfemtomole levels in a label-free manner. Development of a high-throughput nanopore-based biosensor requires multiplexing of nanopore measurements. Electrical detection, however, poses a challenge, as each nanopore circuit must be electrically independent, which requires complex nanofluidics and embedded electrodes. Here, we present an optical method for simultaneous measurements of the ionic current across an array of solid-state nanopores, requiring no additional fabrication steps. Proof-of-principle experiments are conducted that show simultaneous optical detection and characterization of ssDNA and dsDNA using an array of pores. Through a comparison with electrical measurements, we show that optical measurements are capable of accessing equivalent transmembrane current information.

Electrode-embedded nanopores for label-free single-molecule sequencing by electric currents

Electrode-embedded nanopores have been developed to realize label-free, low-cost, and high-throughput DNA sequencers.