Facile One-Step Photochemical Fabrication and Characterization of an Ultrathin Gold-Decorated Single Glass Nanopipette

Monitoring Enzymatic Reaction Kinetics and Activity Assays in Confined Nanospace

Enzyme-mediating biotransformations commonly occur in micro- and nanospace, which is crucial to maintain the essential biochemical processes and physiological functions in living systems. Probing enzyme-catalytic reactions in a biomimetic fashion remains challenging due to the lack of competent tools and methodology. Here, we show that studying enzymatic reaction kinetics can be readily achieved by a well-designed solid-state nanopore. Using tyrosine as a classical substrate, we quantitatively characterize the catalytic activity of tyrosinase (TYR) and tyrosine decarboxylase (TDC) in a nanoconfined space. Tyrosine was first immobilized in the nanopipette, wherein the active sites of tyrosine were left unoccupied. When successively exposed to TYR and TDC, a two-step cascade reaction can spontaneously take place. In this process, the surface wettability and charge of the nanopipette stemming from the catalytic products can sensitively regulate ion transport and ionic current rectification behavior, which were monitored by ionic current signal. In this biomimetic scenario, we obtained the enzymatic reaction kinetics of monophenyl oxidase that were not previously actualized in the conventional macroenvironment. Significantly, TYR showed higher enzyme activity, with a Km value of 1.59 mM, which was lower than that measured in a free and open space (with a Km of 3.01 mM). This suggests that tyrosine should be the most appropriate substrate of TYR, thus improving our understanding of tyrosine-associated biochemical reactions. This work offers an applicable technical platform to mimic enzyme-mediated biotransformations and biometabolisms.

Rectifying artificial nanochannels with multiple interconvertible permeability states

Transmembrane channels play a vital role in regulating the permeation process, and have inspired recent development of biomimetic channels. Herein, we report a class of artificial biomimetic nanochannels based on DNAzyme-functionalized glass nanopipettes to realize delicate control of channel permeability, whereby the surface wettability and charge can be tuned by metal ions and DNAzyme-substrates, allowing reversible conversion between different permeability states. We demonstrate that the nanochannels can be reversibly switched between four different permeability states showing distinct permeability to various functional molecules. By embedding the artificial nanochannels into the plasma membrane of single living cells, we achieve selective transport of dye molecules across the cell membrane. Finally, we report on the advanced functions including gene silencing of miR-21 in single cancer cells and selective transport of Ca2+ into single PC-12 cells. In this work, we provide a versatile tool for the design of rectifying artificial nanochannels with on-demand functions.

In situ monitoring of ROS secretion from single cells with a dual-nanopore biosensor

We report here a dual-nanopore biosensor based on modulation of surface charge density coupled with a microwell array chip for in situ monitoring of ROS secretion from single MCF-7 cells.

Functionalized nanopores based on hybridization chain reaction: Fabrication and microRNA sensing

Enzyme-free hybridization chain reaction (HCR) technology is often used as a signal amplification tool for the detection of different targets. In this study, an ultrasensitive and label-free method for detecting miRNA-21 was developed using the nanopore ionic current rectification (ICR) technology coupled with HCR technology. The probe oligonucleotide (DNA1) was combined with the gold-coated nanopore through the Au-S bond to form a DNA1-functionalized gold-coated nanopore (DNA1-Au-coated nanopore). Since miRNA-21 is partially complementary to DNA1, it can be selectively recognized by DNA1-functionalized gold-coated nanopores. The target (miRNA-21) can induce the opening of hairpin DNA and HCR reaction after the introduction of hairpin DNA H1 and H2. The concentration of miRNA-21 will affect the combination of H1 and H2 on the inner wall of the nanopore, and its surface charge will change with the internal modification, thereby changing the ion current rectification ratio. Under the condition that the concentration of H1, H2 and HCR reaction time are constant, the change of ICR ratio is linearly correlated with the logarithm of miRNA-21 concentration within a certain range, which shows that the sensing strategy we designed can achieve target miRNA-21 detection. This ultrasensitive miRNA holds great promise in the field of cancer diagnosis.

Real-Time Monitoring of Exosomes Secretion from Single Cell Using Dual-Nanopore Biosensors

Exosomes secreted from cells carry rich information from their parent cells, representing a promising biomarker for investigation of diseases. We develop a dual-nanopore biosensor using DNA aptamers to specifically recognize CD63 protein on the exosome's surface, which enables label-free exosome detection based on ionic current change. The sensor allows for sensitive detection of exosomes with a detection limit of 3.4 × 10⁶ particles/mL. The dual-nanopore biosensor was able to form an intrapipette electric circuit for ionic current measurement due to its unique structure, which is crucial to achieve detection of exosome secretion from a single cell. We utilized a microwell array chip to entrap a single cell into a confined microwell with small volume, enabling the accumulation of exosomes with high concentration. The dual-nanopore biosensor was positioned into the microwell with a single cell, and monitoring of exosome secretion from a single cell in different cell lines and under different stimulations has been achieved. Our design may provide a useful platform for developing nanopore biosensors for detecting cell secretions from a single living cell.

G-quadruplex-hemin DNAzyme functionalized nanopipettes: Fabrication and sensing application

Solid-nanopores/nanopipettes have the exquisite ability to reveal the changes in molecular volume due to the advantages of adjustable size, good rigidity and low noise. Herein, a new platform for sensing application was established based on G-quadruplex-hemin DNAzyme (GQH) functionalized gold-coated nanopipettes. In this method, GQH was immobilized on gold-coated nanopipette, which could be used as a catalyst for the reaction of H₂O₂ with 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) to promote the conversion of ABTS to ABTS⁺ ions inside gold-coated nanopipette, and the change of transmembrane ion current could be monitored in real time. At the optimal conditions, there was a correlation between the ion current and the concentration of H₂O₂ in a certain range, which could be used for the hydrogen peroxide sensing. The GQH immobilized nanopipette provides a useful platform to investigate enzymatic catalysis in confined environment, which can be used in electrocatalysis, sensing and fundamental electrochemistry.

Glass Capillary-Based Nanopores for Single Molecule/Single Cell Detection

A glass capillary-based nanopore (G-nanopore), due to its tapered tip, easy tunability in orifice size, and especially its flexible surface modifications that can be tailored to effectively capture and enhance the ionic current signal of single entities (single molecules, single cells, and single particles), offers a powerful and nanoconfined sensing platform for diverse biological measurements of single cells and single molecules. Compared with other artificial two-dimensional solid-state nanopores, its conical tip and high spatial and temporal resolution characteristics facilitate noninvasive single molecule and selected area (subcellular) single cell detections (e.g., DNA mutations, highly expressed proteins, and small molecule markers that reflect the change characteristics of the tumor), as a small G-nanopore (≤100 nm) does negligible damage to cell functions and cell membrane integrity when inserted through the cell membrane. In this brief review, we summarize the preparation of G-nanopores and discuss the advantages of them as solid-state sensing platforms for single molecule and single cell detection applications as well as for cancer diagnosis and treatment applications. We also describe the current bottlenecks that limit the widespread use of G-nanopores in clinical applications and provide an outlook on future developments. The brief review will provide the reader with a quick survey of this field and facilitate the rapid development of a G-nanopore sensing platform for future tumor diagnosis and personalized medicine based on single-molecule/single-cell bioassay.

Electrodeposition of Metal Nanoparticles inside Carbon Nanopipettes for Sensing Applications

Conductive nanopipettes offer promising confined spaces to enable advanced electrochemical sensing applications in small spaces. Herein, a series of metal-decorated carbon nanopipettes (CNPs) were developed, in which Au, Ag, and Pt are modified at the inner walls of CNPs by a simple electrodeposition method. The fabricated tips show good sensing performances for a variety of important analytes, such as glucose, hydrogen peroxide, and chloride and hydrogen ions in biological and catalytic systems. This simple and effective approach can be further extended to prepare other functionalized nanopipette electrodes toward more versatile and powerful measurements in electrochemical sensing and imaging applications.

Glass Nanopore Detection of Copper Ions in Single Cells Based on Click Chemistry

As a common redox metal ion pair in cells, copper ions (Cu²⁺/Cu⁺) often transform between oxidation (Cu²⁺) and reduction (Cu⁺) states. They play important roles in the redox process, so monitoring the change of intracellular copper ions helps understand the redox balance and events in cells. In this study, by self-assembling a thiolated ssDNA (with an alkyne end group) onto a gold-coated glass nanopore (G-nanopore) via the Au-S bond, an alkyne-end single-stranded DNA (ssDNA)-functionalized G-nanopore sensing platform (AG-nanopore) was developed to detect copper ions in cells. In the presence of Cu²⁺ or Cu⁺, the introduction of another ssDNA with an azide group will be ligated with an alkyne group on the functionalized nanopore via a copper-catalyzed azide-alkyne 1,3-cycloaddition (CuAAC) click reaction and hence cause the change of the rectification behavior of the AG-nanopore. The rectification ratio variation of the AG-nanopore had a good response to the intracellular copper ion concentration, and the sensing platform was further applied to the study of the relationship between intracellular oxidative stress and the value of Cu²⁺/Cu⁺.

A highly selective ATP-responsive biomimetic nanochannel based on smart copolymer

ATP-sensitive potassium (K_ATP) channels couple intracellular metabolism to the electrical activity by regulating K⁺ flux across the plasma membrane, thus playing an important role in both normal and pathophysiology. To understand the mechanism of ATP regulating biological ion channels, developing an ATP-responsive artificial nanochannel is an appealing but challenging topic because K_ATP channel is a heteromultimer of two subunits (potassium channel subunit (Kir6.x) and sulfonylurea receptor (SUR)) and exhibit dynamic functions with adjustability and reversibility. Inspired by the structure of K_ATP channels, we designed a smart copolymer modified nanochannel that may address the challenge. In the tricomponent poly(N-isopropylacrylamide) (PNIPAAm, PNI)-based copolymer system, phenylthiourea was used to bind the phosphate units of nucleotides and phenylboronic acid was introduced to combine the pentose ring of the nucleoside unit. Besides, a -COOH group with electron-withdrawing property was added into the phenylthiourea units, which may promote the hydrogen-bond-donating ability of thiourea. Specially, the smart copolymer not only provided static binding sites for recognition but also translated the recognition of ATP into their dynamic conformational transitions by changing the hydrogen-bonding environments surrounding PNIPAAm chains, thus achieving the gating function of nanochannel, which resembled the integration and coordination of Kir6.x and SUR units in active K_ATP. The ATP-regulated ion channel exhibited excellent stability and reversibility. This study is the first example showing how to learn from nature to assemble the ATP-responsive artificial nanochannel and demonstrate the possible mechanism of ATP gating.

Confined Synthesis of Silver Wire at the Nanopipette-Liquid/Liquid Interface

Herein, silver wire is synthesized electrochemically within a nanopipette using the nanopipette-liquid/liquid interface. The i-t curve characterizes the growth state of the silver wire. The higher rate of current increase indicates the faster electron transfer and the faster growth of the silver wire; conversely, when the current does not increase significantly with time, i.e., the rate of increase of the current is small, the growth rate of the silver wire is slow. The main driving force for the growth of silver into a linear structure is the theoretical current differential between the water and oil, caused by the concentration difference between the silver nitrate and ferrocene. The growth of the silver wire is also influenced by the shape of the nanopipette. If the diameter of the pipet increases quickly, silver wire tends to produce multibranched structures, while a smaller diameter makes it easier to obtain silver wire with fewer branches due to the confinement effect. This method is also applicable to the synthesis of gold within a nanopipette. The combination of nanopipette and metallic material using a liquid-liquid interface results in a broader application of nanopipettes for nanopore sensors, nanopore electrodes, bipolar electrodes, etc.

Enzyme-Encapsulated Zeolitic Imidazolate Frameworks Formed Inside the Single Glass Nanopore: Catalytic Performance and Sensing Application

Metal-organic frameworks (MOFs) can improve the stability and activity of enzymes under the MOF encapsulation. However, it remains a challenge to explore the effects of the MOF environment on enzymatic activity in a confined space. In this work, we immobilized the enzyme inside a glass nanopore to study the catalytic activity and stability of the enzyme in the MOF environment. Horseradish peroxidase (HRP) is encapsulated in zeolitic imidazolate framework-90 (ZIF-90) and zeolitic imidazolate framework-8 (ZIF-8), which are used as the catalytic platforms. The HRP can catalyze 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)diammonium salt (ABTS) molecules to generate ABTS⁺ ions, and the change of the transmembrane ion current will be monitored in real time. As the concentration of H₂O₂ increases, the amount of produced ABTS⁺ will increase; thus, the ionic current increases. The effects of the MOF structure on enzyme activity and stability are also investigated. The HRP encapsulated in the MOF and modified inside the nanopore provides a novel and unlabeled design for studying enzymatic catalysis in a confined environment, which should have extensive applications in chemical-/bio-sensing, electrocatalysis, and fundamental electrochemistry.

Electroless deposition of gold nanoparticles on carbon nanopipette electrode for electrochemical detection of catecholamines released from PC12 cells

An electroless deposition method is reported for the fabrication of gold nanoparticles (Au NPs) modified carbon nanopipette electrode (CNPE) for sensitive electrochemical detection of dopamine (DA) in aqueous solution and catecholamines released from PC12 cells. A CNPE is fabricated by chemical vapor deposition with a carbon layer onto nanocapillary and then contacted with copper (Cu) wire. Cu wire of CNPE is able to serve as reducing agent for electroless deposition of Au NPs on the CNPE because the potential of Cu²⁺/Cu is more negative than that of AuCl₄^-/Au. The method is simple, time-saving, and environmentally friendly. Field emission scanning electron microscopy, energy-dispersive X-ray analysis, and electrochemical techniques confirm the successful fabrication of the Au NPs/CNPE. Furthermore, Au NPs/CNPE exhibits a good sensing activity for DA oxidation with a wide linear determination range of 0.1-8 μmol/L and a low detection limit of 6 nmol/L. The Au NPs/CNPE can be potentially applied for measurement of catecholamines released from PC12 cells. This present work is believed to be beneficial to the design and development of active metal catalysts onto nanoelectrodes for the detection of electroactive biological molecules in living cells.Graphical abstract An electroless deposition method was developed for the fabrication of gold nanoparticles onto the carbon nanopipette electrode, which was served as an enhanced electrochemical sensing platform for highly sensitive detection of dopamine with a linear range of 0.1-8 μmol/L and a detection limit of 6 nmol/L, and was also applied in the detection of catecholamines released from PC12 cells.

Analytes Triggered Conformational Switch of i-Motif DNA inside Gold-Decorated Solid-State Nanopores

The nanopore-based technique is a useful tool for single-molecule sensing and characterization. In this work, we have developed a new DNA-functionalized gold-modified nanopore, and analytes can induce the conformational switch of i-motif DNA formed on the inner surface of the nanopore. i-Motif DNA structure can be formed in the presence of silver ions (Ag⁺), which will result in the change in surface charge and structure of the nanopore tip and ion current rectification (ICR) ratio. The i-motif DNA structure on nanopore surface will be destroyed after the addition of glutathione (GSH) due to the strong interaction of Ag-S bond, which results in the recovery of surface charge, steric hindrance, and ICR ratio. This analyte-triggered conformational switch of i-motif DNA can help us deeply understand the DNA technology inside single nanopore and will benefit the possible applications in an ultrasensitive detection and biological/chemical analysis.

Review-Recent Advances in Nanosensors Built with Pre-Pulled Glass Nanopipettes and Their Applications in Chemical and Biological Sensing

Nanosensors built with pre-pulled glass nanopipettes, including bare or chemically modified nanopipettes and fully or partially filled solid nanoelectrodes, have found applications in chemical and biological sensing via resistive-pulse, current rectification, and electrochemical sensing. These nanosensors are easily fabricated and provide advantages through their needle-like geometry with nanometer-sized tips, making them highly sensitive and suitable for local measurements in extremely small samples. The variety in the geometry and layout have extended sensing capabilities. In this review, we will outline the fundamentals in fabrication, modification, and characterization of those pre-pulled glass nanopipette based nanosensors and highlight the most recent progress in their development and applications in real-time monitoring of biological processes, chemical ion sensing, and single entity analysis.

In situ detection of hydroxyl radicals in mitochondrial oxidative stress with a nanopipette electrode

A nanopipette sensor was designed for the in situ detection of ˙OH around mitochondria with high selectivity and sensitivity.

Density Modulation of Embedded Nanoparticles via Spatial, Temporal, and Chemical Control Elements

Nanoparticle polymer composites have enabled material multifunctionalities that are difficult to obtain otherwise. A simple modification to a commercially available resin system enables a universal methodology to embed nanoparticles in resins via spatial, temporal, thermal, concentration, and chemical control parameters. Changes in nanoparticle density distribution are exploited to demonstrate dynamic optical and electronic properties that can be processed on-demand, without the need for expensive equipment or cleanroom facilities. This strategy provides access to the control of optical (cooperative plasmonic effects), electronic (insulator to a conductor), and chemical parameters (multimetal patterning). Using the same composite resin system, the followings are fabricated: i) diffraction gratings with tuneable diffraction efficiencies (10-78% diffraction efficiencies), ii) organic electrochemical transistors with a low drive voltage, and iii) embedded electrodes in confined spaces for potential diagnostic applications.

Rational Design of Stimuli-Responsive Polymers Modified Nanopores for Selective and Sensitive Determination of Salivary Glucose

The great pain and stress from finger-prick glucose measurements have resulted in great motivation to find noninvasive glucose monitoring technologies where salivary glucose measurement is desirable. However, the relative low concentration of glucose and coexisting chemicals in saliva challenges the sensitive and selective salivary glucose detection. In this article, we have rationally designed and constructed a salivary glucose sensor by modifying the inner wall of the Au-decorated glass nanopore with stimuli-responsive copolymer poly(3-(acryloylthioureido) phenylboronic acid-co-N-isopropylacrylamide) (denoted as PATPBA-co-PNIPAAm) via Au-S interaction. Notably, upon recognition of glucose, the copolymer could undergo a wettability switch and pKa shifts in the boronic acid functional groups, which significantly regulated the ion transport through nanopores, thus showing improved sensitivity with the detection limit of 1 nM. Moreover, benefiting from the multivalent boronic acid-glucose interaction and the cooperation of thiourea units, the copolymer exhibited good selectivity for glucose detection against the coexisting saccharides and other biological molecules in saliva. The nanopores with well-demonstrated analytical performance were finally applied for monitoring glucose in saliva. Together, this work unveiled a new platform for glucose detection in saliva, and promised to provide a new strategy for detecting other biomolecules in accessible biofluid involved in physiological and pathological events.

Wireless nanopore electrodes for analysis of single entities

Measurements of a single entity underpin knowledge of the heterogeneity and stochastics in the behavior of molecules, nanoparticles, and cells. Electrochemistry provides a direct and fast method to analyze single entities as it probes electron/charge-transfer processes. However, a highly reproducible electrochemical-sensing nanointerface is often hard to fabricate because of a lack of control of the fabrication processes at the nanoscale. In comparison with conventional micro/nanoelectrodes with a metal wire inside, we present a general and easily implemented protocol that describes how to fabricate and use a wireless nanopore electrode (WNE). Nanoscale metal deposition occurs at the tip of the nanopipette, providing an electroactive sensing interface. The WNEs utilize a dynamic ionic flow instead of a metal wire to sense the interfacial redox process. WNEs provide a highly controllable interface with a 30- to 200-nm diameter. This protocol presents the construction and characterization of two types of WNEs-the open-type WNE and closed-type WNE-which can be used to achieve reproducible electrochemical measurements of single entities. Combined with the related signal amplification mechanisms, we also describe how WNEs can be used to detect single redox molecules/ions, analyze the metabolism of single cells, and discriminate single nanoparticles in a mixture. This protocol is broadly applicable to studies of living cells, nanomaterials, and sensors at the single-entity level. The total time required to complete the protocol is ~10-18 h. Each WNE costs ~$1-$3.

An investigation of solid-state nanopores on label-free metal-ion signalling via the transition of RNA-cleavage DNAzyme and the hybridization chain reaction

Recent advances have proven solid-state nanopores as a powerful analysis platform that enables label-free and separation-free single-molecule analysis. However, the relatively low resolution still limits its application because many chemicals or targets with small sizes could not be recognized in a label-free condition. In this paper, we provide a possible solution that uses solid-state nanopores for small species signaling via the transition of huge DNA assembly products. DNAzyme responding to metal ions and the hybridization chain reaction (HCR) generating nanopore-detectable dsDNA concatamers are used as the transition model set. By the two-step DNAzyme-HCR transition, Pb2+ that was too tiny to be sensed was successfully recognized by the nanopore. The whole process happened in a completely homogeneous solution without any chemical modification. During condition optimization, we also discussed one possible application challenge that may affect the HCR signal-background distinction. Solid-state nanopores provide a potential solution to this challenge due to its ability to profile product length or even 3D structure information.

Surface-Charge Effects on Voltammetry in Carbon Nanocavities

Ion transport controlled by electrostatic interactions is an important phenomenon in biological and artificial membranes, channels, and nanopores. Here, we employ carbon-coated nanopipets (CNPs) for studying permselective electrochemistry in a conductive nanopore. A significant accumulation (up to 2000-fold) of cationic redox species and anion depletion inside a CNP by diffuse-layer and surface-charge effects in a solution of low ionic strength were observed as well as the shift of the voltammetric midpeak potential. Finite-element simulations of electrostatic effects on CNP voltammograms show permselective ion transport in a single conducting nanopore and semiquantitatively explain our experimental data. The reported results are potentially useful for improving sensitivity and selectivity of CNP sensors for ionic analytes.

Amperometric monitoring of vesicular dopamine release using a gold nanocone electrode

We report a facile approach to fabricate a gold nanocone electrode for monitoring dopamine release from individual vesicles.

Exploration of solid-state nanopores in characterizing reaction mixtures generated from a catalytic DNA assembly circuit

Recent advances have proven that using solid-state nanopores is a promising single molecular technique to enrich the DNA assembly signaling library. Other than using them for distinguishing structures, here we innovatively adapt solid-state nanopores for use in analyzing assembly mixtures, which is usually a tougher task for either traditional characterization techniques or nanopores themselves. A trigger induced DNA step polymerization (SP-CHA), producing three-way-DNA concatemers, is designed as a model. Through counting and integrating the translocation-induced current block when each concatemer passes through a glass conical glass nanopore, we propose an electrophoresis-gel like, but homogeneous, quantitative method that can comprehensively profile the "base-pair distribution" of SP-CHA concatemer mixtures. Due to the higher sensitivity, a number of super long concatemers that were previously difficult to detect via gel electrophoresis are also revealed. These ultra-concatemers, longer than 2 kbp, could provide a much enhanced signal-to-noise ratio for nanopores and are thus believed to be more accurate indicators for the existence of a trigger, which may be of benefit for further applications, such as molecular machines or biosensors.

A simple strategy for the fabrication of gold-modified single nanopores and its application for miRNA sensing

A simple strategy was developed for nanopore modification, and was used for miRNA sensing with good sensitivity and selectivity.

The facile approaches to asymmetric modification of glassy biconical microchannel wall with silver, copper or gold

The modification of inner surface has significant influence in the properties of the nano or microchannel based on various materials, especially for the ionic current rectification (ICR) that arises from the selective interaction between ions in solution and the inner surface. Herein, we demonstrate a simple strategy to asymmetrically modify the inner wall of a glassy biconical microchannel with silver, copper or gold by means of silver mirror reaction and polydopamine platform, respectively. And the bidirectional ionic current rectification phenomena were observed in all of the modified biconical microchannels. All of the modification methods are simple, facile and low-cost, and can be applied in the modification of other glassy pipettes.

Fabrication and Use of Nanopipettes in Chemical Analysis

This review summarizes progress in the fabrication, modification, characterization, and applications of nanopipettes since 2010. A brief history of nanopipettes is introduced, and the details of fabrication, modification, and characterization of nanopipettes are provided. Applications of nanopipettes in chemical analysis are the focus in several cases, including recent progress in imaging; in the study of single molecules, single nanoparticles, and single cells; in fundamental investigations of charge transfer (ion and electron) reactions at liquid/liquid interfaces; and as hyphenated techniques combined with other methods to study the mechanisms of complicated electrochemical reactions and to conduct bioanalysis.

Adaption of a Solid-State Nanopore to Homogeneous DNA Organization Verification and Label-Free Molecular Analysis without Covalent Modification

Recent advances have shown increasing designs of nucleic acid organizations via controlling the thermodynamics and kinetics of oligonucleotides. Nevertheless, deeper understanding and further applications of these DNA nanotechnologies are majorly hampered by the lack of effective analytical methodologies that are competent enough to investigate them. To deliver a potential solution, here we developed an innovative exploration that employed the emerging nanopore technique to characterize DNA organization at the single-molecule level and in completely homogeneous condition without covalent modification. With the help of counting and profiling the translocation-induced current drop of a DNA assembly structure passing through a conical glass nanopore (CGN), we have directly verified the formation of the individual double-helix concatemer generated from our model, hybridization chain reaction (HCR). Due to the ultrasensitivity of the nanopore technology, those concatemers that were difficult to observe on a conventional electrophoresis image were brought to light. The translocation duration time also provided the approximate length and folding information for the concatemers. These advantages were proven also applicable to structures with more sophisticated folding behaviors. Eventually, when coupling with an upstream reaction, CGN was further turned to a universal detector that was capable of even detecting other nucleic acid organization behaviors as well as targets that were unable to generate huge products. All of these results are expected to promote deeper study and applications of the nanopore technique in the field of nucleic acid nanotechnology.

Smart Bioinspired Nanochannels and their Applications in Energy-Conversion Systems

Smart bioinspired nanochannels exhibiting ion-transport properties similar to biological ion channels have attracted extensive attention. Like ion channels in nature, smart bioinspired nanochannels can respond to various stimuli, which lays a solid foundation for mass transport and energy conversion. Fundamental research into smart bioinspired nanochannels not only furthers understanding of life processes in living bodies, but also inspires researchers to construct smart nanodevices to meet the increasing demand for the use of renewable resources. Here, a brief summary of recent research progress regarding the design and preparation of smart bioinspired nanochannels is presented. Moreover, representative applications of smart bioinspired nanochannels in energy-conversion systems are also summarized. Finally, an outlook for future challenges in this field is given.

Controllable Shrinking of Glass Capillary Nanopores Down to sub-10 nm by Wet-Chemical Silanization for Signal-Enhanced DNA Translocation

Diameter is a major concern for nanopore based sensing. However, directly pulling glass capillary nanopore with diameter down to sub-10 nm is very difficult. So, post treatment is sometimes necessary. Herein, we demonstrate a facile and effective wet-chemical method to shrink the diameter of glass capillary nanopore from several tens of nanometers to sub-10 nm by disodium silicate hydrolysis. Its benefits for DNA translocation are investigated. The shrinking of glass capillary nanopore not only slows down DNA translocation, but also enhances DNA translocation signal and signal-to-noise ratio significantly (102.9 for 6.4 nm glass nanopore, superior than 15 for a 3 nm silicon nitride nanopore). It also affects DNA translocation behaviors, making the approach and glass capillary nanopore platform promising for DNA translocation studies.

Engineering Single Nanopores on Gold Nanoplates by Tuning Crystal Screw Dislocation

Compared with the large variety of solid gold nanostructures, synthetic approaches for their hollow counterparts are limited, largely confined to chemical and irradiation-based etching of preformed nanostructures. In particular, the preparation of through nanopore structures is extremely challenging. Here, a unique strategy for direct synthesis of gold nanopores in solution without the need for sacrificial templates or postsynthesis processing is reported. By controlling the degree of crystal screw dislocation, a single through pore with diameter ranging from sub-nanometer to tens of nanometers, in the center of large gold nanoplates, can be engineered with precision. Ionic current rectification behaviors are observed using the gold nanopore, potentially enabling new capabilities in biosensing, sequencing, and imaging.

Resistive-pulse and rectification sensing with glass and carbon nanopipettes

Along with more prevalent solid-state nanopores, glass or quartz nanopipettes have found applications in resistive-pulse and rectification sensing. Their advantages include the ease of fabrication, small physical size and needle-like geometry, rendering them useful for local measurements in small spaces and delivery of nanoparticles/biomolecules. Carbon nanopipettes fabricated by depositing a thin carbon layer on the inner wall of a quartz pipette provide additional means for detecting electroactive species and fine-tuning the current rectification properties. In this paper, we discuss the fundamentals of resistive-pulse sensing with nanopipettes and our recent studies of current rectification in carbon pipettes.