Single Nanochannel Research Articles

Micromachining of Polymeric Microfluidic Micro/Nanoelectroporation Device.

Micro/nanochannel electroporation can deliver gene/drug into single cell with precise dosage control and much higher cell viability compared to traditional bulk electroporation. However, single cell micro/nanochannel electroporation has the problems of low efficiency and complicated operation. By integrating microfluidic with micro/nanochannel electroporation, a large number of cells can be processed within a short time. In this chapter, we provide a detailed protocol of fabrication microfluidic nanochannel electroporation devices. The fabrication of this microfluidic nanochannel electroporation device integrates soft lithography, DNA combing and imprinting, and micromilling. This device is appropriate for gene/drug delivery to a batch of cells. It has the advantages of both the single cell nanochannel electroporation and microfluidic based cell manipulation. The procedures of device fabrication, holder fabrication, cell trapping, and electroporation are included in this protocol.

Automated measuring of mass transport through synthetic nanochannels functionalized with polyelectrolyte porous networks

Here we demonstrate the fabrication of porous networks through self-assembly of polyelectrolytes inside nanoconfined geometries. For this purpose, nanochannel membranes fabricated through ion track-etching technique are decorated with an alternate layer-by-layer (LbL) assembly of cationic blend of poly(allylamine hydrochloride)/poly(4-vinylpyridine) (PAH/PVP) and anionic poly(acrylic acid) (PAA) polyelectrolytes. The porous network is prepared by first cross-linking the electrostatic element (PAH and PAA), followed by the removal of hydrogen-bonded polymer (PVP) from the multilayers. In membranes with a single nanochannel, the modification process is monitored by measuring changes in electrolyte ion flux, while the membrane is separating the two compartments of an electrochemical cell. In case of LbL assemblies on multiporous membranes, changes in analyte permeation are presented using an automated analysis of mass transport. Significant decrease in ion current/analyte diffusion across the membranes is caused by LbL assemblies, while an increase is noticed upon removal of hydrogen-bonded PVP from the multilayers, indicating the formation of porous networks. We believe that our presented method for the automated recording of analyte transport in combination with a new modification procedure can be potentially applicable in ionic/molecular separation, drug delivery processes, and for the monitoring of triggered releases of drugs.

Preparation of Single Cu Nanowire and in-situ Study of Its Electrical Properties

Metal nanowires, as one of the most crucial components of nanoelectronic devices in the future, have attracted enormous attention. Therefore, it is of great significance to investigate the electrical properties of single metal nanowires. Herein, the single Cu nanowire with diameter of 64 nm was successfully prepared by using single-ion track template method combined with electrochemical deposition approach, and its I-V curve was measured. Such a diameter represents the thinnest one as comparing the reported ones obtained by the same method. The results illustrated that the process of formation and growth, as well as the final diameter of single nanochannel in template can be monitored and measured by conductance method. During the electrochemical deposition, the dynamic evolution of the deposition of nanowire can be clearly reflected through the deposition current and deposition time. At the same time, I-V measurements reveal that the Cu nanowire has typical metallic characteristic. For the first time, the resistivity of such a thin nanowire is obtained and its resistivity is 3.46 μΩ·cm which is around twice that of Cu bulk materials. The increase of resistivity is believed coming from finite size effects and may be related to the electrons scattering at the grain boundaries and surfaces.

Effects of ion size, ion valence and pH of electrolyte solutions on EOF velocity in single nanochannels

Electroosmotic flow (EOF) in nanochannels as small as 85 nm and in small microchannels is systematically investigated by using the current-slope method. The effects of ion size, ion valence and pH of electrolyte solutions on the velocity of electroosmotic flow are experimentally studied. The results show that the large size of hydrated ions leads to higher EOF velocity in large nanochannels and microchannels, and, however, lower EOF velocity in small nanochannels with an overlapped electric double layer (EDL). Furthermore, the EOF velocity is proportional to the pH of the electrolyte solution and contrariwise proportional to the valence of counter-ions. It is also observed that the EOF velocity depends on the channel size in nanochannels, even without overlapped EDL. Several models of electric double layer (EDL) are proposed to explain the experimental results and provide an improved understanding of the effects of ion size, ion valence and pH of electrolyte solutions on the EOF velocity in nanochannels in terms of EDL structure.

Polymer in MOF Nanospace: from Controlled Chain Assembly to New Functional Materials

AbstractPreparation of composites by inclusion of polymers inside metal‐organic frameworks (MOFs) is a very powerful strategy to prepare innovative functional materials. MOF's nanosized pores disrupt polymer chains natural coiling and constrain them in an extended conformation, bringing new properties. At the single nanochannel scale, polymerization reactions are significantly modified due to confinement, and control over the primary structure (sequence, tacticity or branching) can be achieved. Because of confinement and chain extension, physical and chemical properties can also be significantly improved compared to the bulk state. Inclusion is also useful to control organization at a higher scale, for instance for precise polymer positioning or by acting as scaffold for an accessible microporous polymer network. Furthermore, the MOF ordering can be maintained in pure polymer systems even after removal of the host.

Engineered Artificial Nanochannels for Nitrite Ion Harmless Conversion.

Inspired by the delicate functions of living organisms to transport or transform nitrite ions (NO2-), a bioinspired smart nanochannel that can realize harmless conversion of NO2- into N2 is developed by immobilizing a NO2--responsive functional molecule, p-phenylenediamine, onto a single conical polyethylene terephthalate nanochannel. Subsequently, the aromatic primary amine groups could be triggered to transform into a phenyldiazonium molecule based on the acid-activated NO2--binding process. The nanochannel exhibits specific selectivity and highly ultratrace recognition of NO2-. Fascinatingly, the transformed phenyldiazonium molecules could be triggered to generate phenol groups and release N2 by ultraviolet light activation, achieving NO2- harmless conversion. This system could provide inspiration to construct artificial nanofluidic devices for ion-sensing and nitrogen cycle fields.

A Direct Sensor to Measure Minute Liquid Flow Rates.

Nanofluidics finds its root in the study of fluids and flows at the nanoscale. Flow rate is a quantity that is both central when dealing with flows and notoriously difficult to measure experimentally at the scale of an individual nanopore or nanochannel. We show in this letter that minute flow rate can be directly measured accumulating liquid over time within the compliant membrane of a commercial piezoresistive pressure sensor. Our flow rate sensor is versatile and can be operated independently of the nature of the liquid, flow profile, and type of nanochannel. We demonstrate this method by measuring the pressure-driven flow of silicon oil in a single nanochannel of average radius 200 nm. This approach gives reliable measurement of the flow rate up to 1 pL/min. Unlike other nanoscale flow measurements methods based, for instance, on particle tracking, our sensor delivers a direct voltage output suitable for nanoflow control applications.

Renormalization of Ionic Solvation Shells in Nanochannels.

Recently, experimental studies on selective ion transport across nanoporous membranes or through single nanochannels have unveiled interesting behaviors of dissolved ions under nanoconfinement. However, the exploration was limited by the resolution of experimental characterization. In this work, we present an atomistic simulation-based study, showing how the nanoconfinement and surface functionalization of graphene and graphene oxide nanochannels renormalize the solvation of ions (Na+, K+, Mg2+, Ca2+, Cl-). We find that the spatial distribution of dissolved ions demonstrates a layered order in nanochannels. The 1st hydration shell structures of cations are well defined in channels with width beyond ∼1.0 nm, although the rotational degree of freedom is constrained, while the 2nd hydration shells could be destructed. In the graphene oxide nanochannels, oxygen-containing functional groups can participate in the hydration shells of univalent ions but not for the divalent ions, and the valence-dependent reduction in the ionic diffusivity offers good selectivity between the divalent and univalent ions with the interlayer spacing of ∼1.0 nm, which is absent in the graphene nanochannels. With these findings, we conclude that the assessment of permeability and selectivity of ions has to take the renormalized nature of ionic solvation shells into account in the design of nanoporous membranes or nanofluidic devices for energy and environmental applications.

Single- to Few-Layered, Graphene-Based Separation Membranes.

Two-dimensional, graphene-based materials have attracted great attention as a new membrane building block, primarily owing to their potential to make the thinnest possible membranes and thus provide the highest permeance for effective sieving, assuming comparable porosity to conventional membranes and uniform molecular-sized pores. However, a great challenge exists to fabricate large-area, single-layered graphene or graphene oxide (GO) membranes that have negligible undesired transport pathways, such as grain boundaries, tears, and cracks. Therefore, model systems, such as a single flake or nanochannels between graphene or GO flakes, have been studied via both simulations and experiments to explore the transport mechanisms and separation potential of graphene-based membranes. This article critically reviews literature related to single- to few-layered graphene and GO membranes, from material synthesis and characteristics, fundamental membrane structures, and transport mechanisms to potential separation applications. Knowledge gaps between science and engineering in this new field and future opportunities for practical separation applications are also discussed.

Single Nanochannel-Aptamer-Based Biosensor for Ultrasensitive and Selective Cocaine Detection.

Ultrasensitive and selective detection of molecules at nano or sub-nanomolar level is very important for many areas such as early diagnosis and drug testing. Herein, we report a high-sensitive cocaine sensor based on a single nanochannel coupled with DNA aptamers. The single nanochannel-aptamer-based biosensor can recognize cocaine molecules with an excellent sensitivity and good selectivity. A linear relationship between target cocaine concentration and output ionic current is obtained in a wide concentration range of cocaine from 1 nM to 10 μM. The cocaine sensor also shows a detection limit down to 1 nM. This study provides a new avenue to develop new nanochannel-aptamer-based biosensors for rapid and ultratrace detection of a variety of illicit drugs.

Fast water transport in graphene nanofluidic channels.

Superfast water transport discovered in graphitic nanoconduits, including carbon nanotubes and graphene nanochannels, implicates crucial applications in separation processes and energy conversion. Yet lack of complete understanding at the single-conduit level limits development of new carbon nanofluidic structures and devices with desired transport properties for practical applications. Here, we show that the hydraulic resistance and slippage of single graphene nanochannels can be accurately determined using capillary flow and a novel hybrid nanochannel design without estimating the capillary pressure. Our results reveal that the slip length of graphene in the graphene nanochannels is around 16 nm, albeit with a large variation from 0 to 200 nm regardless of the channel height. We corroborate this finding with molecular dynamics simulation results, which indicate thatthis wide distribution of the slip length is due to the surface charge of graphene as well as the interaction between graphene and its silica substrate.

Corrigendum: A Sequential Recognition for Zinc Ion and Pyrophosphate Based on a Terpyridine Derivative-Functionalized Single Nanochannel.

Prof. Yuqi Zhang,[a,b] Ru Zhou,[a,b] Dr. Zhiju Zhao,[c] Dr. Xiang-Yu Kong,*[a,b] Ganhua Xie,[d] Dr. Qian Liu,[c] Pei Li,[e] Zhen Zhang,[d] Kai Xiao,[d] Prof. Zhengping Liu,[c] Prof. Liping Wen,*[b] and Prof. Lei Jiang[b,e] [a] College of Chemistry & Chemical Engineering, Shaanxi Key Laboratory of Chemical Reaction Engineering, Yan′an University, Yan′an, Shaanxi, 716000 (P. R. China) Email: [email protected] [b] Key Laboratory of Bio-inspired Materials and Interfacial Science, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing, 100190 (P. R. China) E-mail: [email protected] [c] Beijing Key Laboratory of Energy Conversion and Storage Materials, College of Chemistry, Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, Beijing Normal University, Beijing, 100875 (P. R. China) [d] Key Laboratory of Green Printing, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190 (P. R. China) [e] Key Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education, School of Chemistry and Environment, Beihang University, Beijing, 100191 (P. R. China) In the above article, the institutional affiliations of the authors were incorrectly assigned. The correct affiliations are as given above. The authors apologize for this oversight.

Anomalous Ionic Conductance in Carbon Nanotube Nanochannels

Simulations and experimental studies have reported an unusually high ionic conductance in carbon nanotube (CNT) nanochannels. The origin of this phenomenon is, however, poorly-understood: literature reports often disagree in the magnitude of the different transport mode contributions to the measured ionic current and even in what ions are actually carrying the current; moreover, results obtained with single pore measurements differ frequently from those with membranes containing billions of open CNT channels, i.e. the average CNT behavior. Toward shedding light on these phenomena, we fabricated a novel nanofluidic platform having a >30-nm wide, FIB-nanomachined silicon nitride nanopore (SiNx) in series with vertically-aligned sub-5 nm carbon nanotubes, the number of which can be controlled from one to billions. By employing this platform with only one or a few open CNTs, we observed giant ionic currents in CNT channels and a power-law increase of conductance with KCl concentration (G ∼ cn, n=0.1-0.4), a dependence that seems to be unique of CNT pores. A few literature reports attributed this giant ionic current in CNTs to a strong electro-osmotic flow. To quantify electro-osmosis in CNT pores, we investigated translocation of neutral molecules in a single CNT nanochannel with the resistive pulse technique. Furthermore, we employed finite element analysis to elucidate the relationship between CNT pore characteristics (e.g., size, surface charge, slip length) and the resulting ionic transport and magnitude of the electro-osmotic component. We confirmed computationally that the unusually large conductance in our experimental platform results from the presence of a strong electro-osmotic coupling between the CNT channel and the SiNx nanopore in series with it. Finally, we apply first-principle simulations to show that cation-CNT interactions may help explain the origin of this electro-osmotic flow.

Electrokinetic motion of single nanoparticles in single PDMS nanochannels

Electrokinetic motion of single nanoparticles in single nanochannels was studied systematically by image tracking method. A novel method to fabricate PDMS-glass micro/nanochannel chips with single nanochannels was presented. The effects of ionic concentration of the buffer solution, particle-to-channel size ratio and electric field on the electrokinetic velocity of fluorescent nanoparticles were studied. The experimental results show that the apparent velocity of nanoparticles in single nanochannels increases with the ionic concentration when the ionic concentration is low and decreases with the ionic concentration when the concentration is high. The apparent velocity decreases with the particle-to-channel size ratio (a/b). Under the condition of low electric fields, nanoparticles can hardly move in single nanochannels with a large particle-to-channel size ratio. Generally, the apparent velocity increases with the applied electric field linearly. The experimental study presented in this article is valuable for future research and applications of transport and manipulation of nanoparticles in nanofluidic devices, such as separation of charged nanoparticles and DNA molecules.

Periodic oscillation of ion conduction of nanofluidic diodes using a chemical oscillator.

Periodic ion-conduction oscillation of biological ion channels in a living system is essential for numerous life processes. Here we report an oscillatory nanofluidic system that can self-regulate its ion-conduction states under constant conditions. The oscillatory nanofluidic system is constructed by integrating a chemical oscillator into an artificial single nanochannel system. Oscillating chemical reactions of the pH oscillator carried out inside the nanochannel are used to switch the surface properties of the channel between highly and lowly charged states, thus realizing an autonomous, continuous and periodic oscillation of the ion conductance of the channel between high and low ion-conduction states. The ion-conduction switching is characterized by the periodic ion current oscillation of the nanochannel measured under constant conditions. The oscillation period of the nanofluidic devices decreased gradually with increasing the working temperature. This study is a potential step toward the ability to directly convert chemical energy to ion-conduction oscillation in nanofluidics. On the basis of these findings, we believe that a variety of artificial oscillatory nanofluidic systems will be achieved in future by integrating artificial functional nanochannels with diverse oscillating chemical reactions.

Single Nanochannel Platform for Detecting Chiral Drugs.

Chiral drugs play an essential role in medical and biochemical systems, and thus enantioselective analysis of chiral molecules has become a central focus in chemical, biological, medical, and pharmaceutical research. The design of chiral drug-detecting systems is a long-term and challenging task. Here we report the use of a modification-free nanochannel method for enantioselective recognition of S-naproxen from R-naproxen using N-acetyl-l-cysteine-capped gold nanoparticles as a chiral selector. The chiral discrimination is based on a drug-induced nanoparticle diastereoselective aggregation mechanism that blocks ion transport through the nanochannel. We demonstrated that high S-Npx selectivity in both water and biological samples can be achieved. This simple method has potential applications as a general platform for the detection of chiral molecules.

Sequential Recognition of Zinc and Pyrophosphate Ions in a Terpyridine-Functionalized Single Nanochannel.

A highly selective recognition system for zinc(II) and pyrophosphate ions is constructed using a single conical nanochannel covalently functionalized with N'-{4-[(2,2':6',2''-terpyridine)-4-yl]benzyl}ethane-1,2-diamine (TPYD). The immobilized TPYD acts as a specific coordination site for Zn2+ to form TPYD-Zn2+ complexes in preference over other metal ions, and subsequently, the resulting Zn2+ -coordinated nanochannel can be used as a selective recognition element for the pyrophosphate ion based on the coordination reaction between hydroxyl oxygen atoms of pyrophosphate and Zn2+ . Ion recognition is monitored by measuring the current-voltage curves of the solutions. The ionic current of the TPYD-functionalized system at -2.0 V undergoes a clear decrease after exposure to Zn2+ ions and is followed with an obvious increase after subsequent treatment with a pyrophosphate solution. The change of ionic current can be primarily attributed to the variation of charge density of the nanochannel. This functionalized single nanochannel might provide a simple and universal means to recognize other targets by modifying different functional molecules onto the inner surfaces of nanochannels.

Supramolecular Self-Assembly Induced Adjustable Multiple Gating States of Nanofluidic Diodes.

Artificial nanochannels, inheriting smart gating functions of biological ion channels, promote the development of artificial functional nanofluidic devices for high-performance biosensing and electricity generation. However, gating states of the artificial nanochannels have been mainly realized through chemical modification of the channels with responsive molecules, and their gating states cannot be further regulated once the nanochannel is modified. In this work, we employed a new supramolecular layer-by-layer (LbL) self-assembly method to achieve reversible and adjustable multiple gating features in nanofluidic diodes. Initially, a self-assembly precursor was modified into a single conical nanochannel, then host molecule-cucurbit[8]uril (CB[8]) and guest molecule, a naphthalene derivative, were self-assembled onto the precursor through an LbL method driven by host-enhanced π-π interaction, forming supramolecular monolayer or multilayers on the inner surface of the channel. These self-assemblies with different layer numbers possessed remarkable charge effects and steric effects, exhibiting a capability to regulate the surface charge density and polarity, the effective diameter, and the geometric asymmetry of the single nanochannel, realizing reversible gating of the single nanochannel among multiple rectification and ion-conduction states. As an example of self-assembly of supramolecular networks in nanoconfinements, this work provides a new approach for enhancing functionalities of artificial nanochannels by LbL supramolecular self-assemblies. Meanwhile, since the host molecule, CB[8], used in this work can interact with different kinds of biomolecules and stimuli-responsive chemical species, this work can be further extended to build a novel stable multiple-state research platform for a variety of uses such as sensing and controllable release.

Single Particle Nanoplasmonic Sensing in Individual Nanofluidic Channels.

Nanoplasmonics allows label-free optical sensing and spectroscopy at the single nanoparticle level by exploiting plasmonic excitations in metal nanoparticles. Nanofluidics offers exclusive possibilities for applying and controlling fluid flow and mass transport at the nanoscale and toward nanosized objects. Here, we combine these two concepts in a single device, by integrating single particle nanoplasmonic sensing with nanofluidics using advanced nanofabrication. The developed devices enable on-chip referenced parallel single particle nanoplasmonic sensing inside multiple individual nanofluidic channels with dimensions down to the 100 nm range. Beyond detailed discussion of the nanofabrication, general device characterization, and parallelized single particle plasmonic readout concepts, we demonstrate device function on two examples: (i) in situ measurements of local buffer concentrations inside a nanofluidic channel; (ii) real time binding kinetics of alkanethiol molecules to a single plasmonic nanonatenna sensor in a single nanochannel. Our concept thus provides a powerful solution for controlling mass transport to and from individual (plasmonic) nanoparticles, which in a long-term perspective offers unique opportunities for label-free detection of analyte molecules at low concentrations and for fundamental studies of fluids in extreme confinement.

Accurate measurement of liquid transport through nanoscale conduits.

Nanoscale liquid transport governs the behaviour of a wide range of nanofluidic systems, yet remains poorly characterized and understood due to the enormous hydraulic resistance associated with the nanoconfinement and the resulting minuscule flow rates in such systems. To overcome this problem, here we present a new measurement technique based on capillary flow and a novel hybrid nanochannel design and use it to measure water transport through single 2-D hydrophilic silica nanochannels with heights down to 7 nm. Our results show that silica nanochannels exhibit increased mass flow resistance compared to the classical hydrodynamics prediction. This difference increases with decreasing channel height and reaches 45% in the case of 7 nm nanochannels. This resistance increase is attributed to the formation of a 7-angstrom-thick stagnant hydration layer on the hydrophilic surfaces. By avoiding use of any pressure and flow sensors or any theoretical estimations the hybrid nanochannel scheme enables facile and precise flow measurement through single nanochannels, nanotubes, or nanoporous media and opens the prospect for accurate characterization of both hydrophilic and hydrophobic nanofluidic systems.