Large Nanopores Research Articles

Direct Electrochemistry of Glucose Oxidase on a Three-Dimensional Porous Zirconium Phosphate–Carbon Aerogel Composite

Biocompatible materials with large specific surface areas can play a crucial role in direct electron transfer between redox proteins and an electrode surface. Here, we report zirconium phosphate–carbon aerogel (ZrP-CA) composites with a large specific surface area and uniform nanopore distributions as matrix for glucose oxidase immobilization. The immobilized glucose oxidase displays two stable, well-defined redox peaks with an electron transfer rate constant of 9.34 s−1 in nitrogen-saturated phosphate-buffered saline (PBS) solution (0.1 M, pH 7.0), at a scan rate of 100 mV s−1. The modified electrode was also used as a glucose biosensor, which was found to exhibit a linear calibration range of 0.12–2.0 mM, sensitivity of 5.56 μA mM−1 cm−2 at an applied potential of −0.5 V, and detection limit of 34 μM based on a signal-to-noise ratio of 3. After 80 scan cycles, the decreases in the peak current were less than 8 %, indicating good stability of the as-prepared ZrP-CA. The unique characteristics of the ZrP-CA nanocomposite make it a good matrix for protein immobilization and biosensor preparation.

Multiscale characterization of arabinoxylan and β-glucan composite films

Composite films made with Arabinoxylans (AXs) (with high, middle and low level of substitution by arabinose) and (1→3)(1→4)-β-d-glucans (BGs) extracted from cereal cell walls have been prepared and analyzed using microscopy (SEM and LSCFM), DSC, mechanical tests and TD-NMR spectroscopy. The objectives were to correlate molecular and physico-chemical properties of films with mechanical and hydration properties of wheat cell walls. A phase separation phenomenon was observed for films made with highly substituted AXs and BGs at a ratio AX/BG of 60/40. This phase separation was correlated with lower dipolar interactions between polysaccharide chains and a decrease of ultimate strain and stress of films. Highly substituted AX and BG composite films exhibited very weak mechanical properties in agreement with weaker interactions between the polymer chains. This effect was supported by NMR results showing that interactions between AXs and BGs decreased with increased substitution of AXs in composite films. Lower dipolar interactions between polysaccharides favored the water mobility in relation with a higher specific surface area of polysaccharides in films but also higher distances between polysaccharide chains so larger nanopores in composite films made within highly substituted AXs. These multiscale characterizations agreed with the structural changes observed in wheat grain during its development.

KF promoted mesoporous γ-Al2O3 with strong basicity: Preparation, characterization and catalytic activitiy for transesterification to biodiesel

The present paper describes the preparation of KF/M-γ-Al2O3, efficient mesoporous solid bases. The procedure involves loading KF into a crystalline mesoporous γ-Al2O3 that was synthesized by the self-assembly of poly-4-vinylpyridine (P4VP) with Al3+ species. The synthesis is based on the strong acid-base interaction, hydrothermal treatment at 180°C and calcination at 550°C. Characterizations using XRD analysis and low temperature N2 adsorption indicated that different amounts of KF could be introduced into crystalline mesoporous γ-Al2O3 to obtain catalysts with high BET surface areas, large pore volumes and uniform pore size distribution. Based on SEM images, KF/M-γ-Al2O3 catalysts have rough surface character and a large nanopore volume. CO2-TPD curves registered for KF/M-γ-Al2O3 contain high temperature peaks, indicating strong basicity of the catalysts. Under the same reaction conditions KF/M-γ-Al2O3 catalysts exhibit much better activities for transesterification to biodiesel than KOH, NaOH, H2SO4, hydrotalcite and CaO. Enhanced activities appear to arise from strong basisity and large BET surface areas.

Electrically facilitated translocation of protein through solid nanopore

Nanopores have been proven as versatile single-molecule sensors for individual unlabeled biopolymer detection and characterization. In the present work, a relative large nanopore with a diameter of about 60 nm has been used to detect protein translocation driven by a series of applied voltages. Compared with previous studied small nanopores, a distinct profile of protein translocation through a larger nanopore has been characterized. First, a higher threshold voltage is required to drive proteins into the large nanopore. With the increase of voltages, the capture frequency of protein into the nanopore has been markedly enhanced. And the distribution of current blockage events is characterized as a function of biased voltages. Due to the large dimension of the nanopore, the adsorption and desorption phenomenon of proteins observed with a prolonged dwell time has been weakened in our work. Nevertheless, the protein can still be stretched into an unfolded state by increased electric forces at high voltages. In consideration of the high throughput of the large nanopore, a couple of proteins passing through the nanopore simultaneously occur at high voltage. As a new feature, the feasibility and specificity of a nanopore with distinct geometry have been demonstrated for sensing protein translocation, which broadly expand the application of nanopore devices.

Fabrication of Graphene Nanopores and a Preliminary Study onλ-DNA Translocation

Nanopore sequencing is among the most promising technologies to achieve the goals of the "$1,000 Genome." Two major types of nanopores have been extensively investigated, protein and silicon-based solid-state nanopores. However, protein pores are short-lived and the length of solid-state nanopores is much larger than the distance between adjacent bases, resulting in incapability to discriminate individual bases along the single-stranded DNA molecules. In this paper, we report λ-DNA translocations through graphene nanopore. A large nanopore with diameter of about 30 nm on silicon nitride substrates were first fabricated using focused ion beam(FIB) system under the beam current of 2 pA, accelerating voltage of 30 kV and sculpting time of 1 s. Individual graphene membranes were suspended onto the substrates to cover the large pore, and nanopores with a diameter less than 10 nm are sculpted in the graphene sheet by focused electron beam(FEB) from a transmission electron microscope(TEM) under a 400 kx magnification times and 300 kV accelerating voltage at 1×105~5×105A/m2 current density for 2~3 min. The edges of these graphene nanopores became smoother and sharper when the temperature was increased to about 450 ℃, which might help to lower interactions between graphene nanopores and the analytes. The signals of DNA translocation through graphene nanopores had been recorded using a patch clamp amplifier at 10 kHz sampling frequency filtered at 5 kHz via an integrated four-pole low-pass Bessel filter. Analyses of the DNA translocation current traces indicated that different conformations of DNA molecules may exist during entrance into nanopores. In addition, our overall detection platform had a low noise amplitude of around 10 pA, which allowed more sensitive signal detection. Taken together, our observations demonstrate that graphene nanopores are feasible for DNA sensing, leading a forward step towards single-molecule DNA sequencing using monolayered graphene nanopores.

Nanotubes Complexed with DNA and Proteins for Resistive-Pulse Sensing

We use a resistive-pulse technique to analyze molecular hybrids of single-wall carbon nanotubes (SWNTs) wrapped in either single-stranded DNA or protein. Electric fields confined in a glass capillary nanopore allow us to probe the physical size and surface properties of molecular hybrids at the single-molecule level. We find that the translocation duration of a macromolecular hybrid is determined by its hydrodynamic size and solution mobility. The event current reveals the effects of ion exclusion by the rod-shaped hybrids and possible effects due to temporary polarization of the SWNT core. Our results pave the way to direct sensing of small DNA or protein molecules in a large unmodified solid-state nanopore by using nanofilaments as carriers.

Ion selection of charge-modified large nanopores in a graphene sheet

Water desalination becomes an increasingly important approach for clean water supply to meet the rapidly growing demand of population boost, industrialization, and urbanization. The main challenge in current desalination technologies lies in the reduction of energy consumption and economic costs. Here, we propose to use charged nanopores drilled in a graphene sheet as ion exchange membranes to promote the efficiency and capacity of desalination systems. Using molecular dynamics simulations, we investigate the selective ion transport behavior of electric-field-driven KCl electrolyte solution through charge modified graphene nanopores. Our results reveal that the presence of negative charges at the edge of graphene nanopore can remarkably impede the passage of Cl(-) while enhance the transport of K(+), which is an indication of ion selectivity for electrolytes. We further demonstrate that this selectivity is dependent on the pore size and total charge number assigned at the nanopore edge. By adjusting the nanopore diameter and electric charge on the graphene nanopore, a nearly complete rejection of Cl(-) can be realized. The electrical resistance of nanoporous graphene, which is a key parameter to evaluate the performance of ion exchange membranes, is found two orders of magnitude lower than commercially used membranes. Our results thus suggest that graphene nanopores are promising candidates to be used in electrodialysis technology for water desalinations with a high permselectivity.

Copolymer—homopolymer mixtures in a nanopore

We have performed the cell dynamics simulation with the time-dependent Ginzburg—Landau theory to study the self-assembled morphology of A—B diblock copolymers and C homopolymers in a neutral nanopore. The nanopore diameter and length are systematically varied to examine their effects on the structures of various morphologies and their phase transition. From the simulation, it is observed that the equilibrium morphology of the confined system is sensitive to pore diameter D and pore length Lpore, the phase behavior in neutral nanopores is due to an interplay of two factors: the surface effect and the extension effect. When the nanopore length and the lamellae spacing are not commensurate, the surface effect prevails at small nanopores (small diameters or short lengths), the extension effect takes over at larger nanopores (large diameters or long lengths). When the nanopore length and the lamellae spacing are commensurate, the surface effect dominates. Furthermore, the interactions between different monomers are also discussed and we obtain a transition from a tilted pancakes/cylinder structure (Ltilted⊥) to a concentric cylindrical structure with defects and to a concentric cylindrical structure (L‖). We also investigate the effect of the relative concentrations of diblock copolymer—homopolymer and obtain a transition in which the position of the C blocks changes from the outer of the cylinder to the middle of the cylinder and then to the inner of the cylinder with the concentration of the C blocks decreasing.

Highly Selective Macrocycle Formations by Metathesis Catalysts Fixated in Nanopores

Ruthenium-based metathesis catalysts immobilized on mesocellular siliceous foam (MCF) bearing large nanopores proved highly efficient and selective for macrocyclic ring-closing metathesis (RCM). Kinetic studies revealed that the homogeneous counterpart exhibited far higher activity that accounted for more oligomerization pathways and resulted in less macrocyclization products. Meanwhile, the immobilized catalysts showed lower conversion rates leading to higher yields of macrocyclic products in a given reaction time, with conversion rates and yields dependent upon pore size, catalyst loading density, and linker length. The macrocycle formations via RCM were accelerated by increasing the pore size and decreasing the catalyst loading density while retaining the comparably high yield. The catalysts immobilized on MCF, of which silica surface is rigid and pores are relatively large, showed high conversion rates and yields compared with an analogue immobilized on TentaGel resins, of which backbone becomes flexible upon swelling in the reaction medium. It is noteworthy that the selectivity for the macrocyclic RCM can be significantly improved by tuning the catalyst initiation rates via immobilization onto the support materials in which well-defined three-dimentional network of large nanopores are deployed.

Yttrium-modified Li4Ti5O12as an effective anode material for lithium ion batteries with outstanding long-term cyclability and rate capabilities

Yttrium-modified Li4Ti5O12 (YLTO) was fabricated by a coprecipitation method using tetrabutyl titanate, Y(NO3)3·6H2O and LiOH·H2O as reactants, followed by simply sintering the dried mixture at 600 °C. The products and their lithiation–delithiation process were characterized by a combination of electrochemical measurements, X-ray diffraction, transmission electron microscopy and nitrogen adsorption. The YLTO exhibits excellent long-term cycling stability (over 1000 cycles) at a high current rate of 10 C and outstanding rate capabilities. Particularly, the YLTO demonstrates remarkable cyclability even if directly cycled at a rate of 10 C without low-rate activation and with no relaxation between charge and discharge. Even without utilizing carbon black as conductive material, the YLTO still shows prominent rate capabilities and long-term cyclic performance at a rate of 5 C. The excellent performance is ascribed to the increased lattice constant, improved electronic and ionic conductivities, refined grains with large surface area and uniform nanopores resulting from the Y-modification.

Reverse-biomineralization assembly of acid-sensitive biomimetic fibers for hard tissue engineering and drug delivery.

Biomimetic design and fabrication of tissue-engineered bone scaffolds that not only resemble natural bone in structure and performance, but also are endowed with specific functions, e.g., for drug delivery, are always an exciting research area. Herein, we report a kind of doxorubicin hydrochloride-loaded biomimetic ultrathin fiber, which is synthesized by preparing a kind of nanoporous bioactive glass fiber as a drug/protein carrier and bio-template and combining them in a reverse-biomineralization reaction. Protein adsorption experiments demonstrate that bovine serum albumin can be hosted in open large nanopores of bioactive glass fibers and the adsorption mechanism follows the intraparticle diffusion process. Biomineralization shows that proteins and drugs can be integrated at the nanoscale into minerals to form biomimetic and drug-loaded fibers, and the formation of such fibers depends on the functional ion (Ca, P, and Si) release of bioactive glass fibers and electrostatic interaction among bioactive glass fibers, proteins, and drugs. The drug-loaded composite fibers demonstrate bare homogeneous solid matrices in the fiber interior and surfaces upon which amorphous carbonated apatite resides. The drug release profiles show that the as-synthesized fibers are acid-sensitive and drugs can be released at pH 5, but not at neutral pH 7.4. Because of their structural advantages and the characteristics of acid-sensitive drug release, the biomimetic fibers have potential applications for repairing the bone defects resulting from tumour extirpation.

An Electron Paramagnetic Resonance Spectroscopy Investigation of the Retention Mechanisms of Mn and Cu in the Nanopore Channels of Three Zeolite Minerals

AbstractThe adsorption mechanisms of divalent cations in zeolite nanopore channels can vary as a function of their pore dimensions. The nanopore inner-sphere enhancement (NISE) theory predicts that ions may dehydrate inside small nanopore channels in order to adsorb more closely to the mineral surface if the nanopore channel is sufficiently small. The results of an electron paramagnetic resonance (EPR) spectroscopy study of Mn and Cu adsorption on the zeolite minerals zeolite Y (large nanopores), ZSM-5 (intermediate nanopores), and mordenite (small nanopores) are presented. The Cu and Mn cations both adsorbed via an outer-sphere mechanism on zeolite Y based on the similarity between the adsorbed spectra and the aqueous spectra. Conversely, Mn and Cu adsorbed via an inner-sphere mechanism on mordenite based on spectrum asymmetry and peak broadening of the adsorbed spectra. However, Mn adsorbed via an outer-sphere mechanism on ZSM-5, whereas Cu adsorbed on ZSM-5 shows a high degree of surface interaction that indicates that it is adsorbed closer to the mineral surface. Evidence of dehydration and immobility was more readily evident in the spectrum of mordenite than in that of ZSM-5, indicating that Cu was not as close to the surface on ZSM-5 as it was when adsorbed on mordenite. Divalent Mn cations are strongly hydrated and are held strongly only in zeolites with small nanopore channels. Divalent Cu cations are also strongly hydrated, but can dehydrate more easily, presumably due to the Jahn-Teller effect, and are held strongly in zeolites with medium-sized nanopore channels or smaller.

Fabrication and characterization of nanopores with insulated transverse nanoelectrodes for DNA sensing in salt solution

We report on the fabrication, simulation, and characterization of insulated nanoelectrodes aligned with nanopores in low-capacitance silicon nitride membrane chips. We are exploring these devices for the transverse sensing of DNA molecules as they are electrophoretically driven through the nanopore in a linear fashion. While we are currently working with relatively large nanopores (6-12 nm in diameter) to demonstrate the transverse detection of DNA, our ultimate goal is to reduce the size sufficiently to resolve individual nucleotide bases, thus sequencing DNA as it passes through the pore. We present simulations and experiments that study the impact of insulating these electrodes, which is important to localize the sensing region. We test whether the presence of nanoelectrodes or insulation affects the stability of the ionic current flowing through the nanopore, or the characteristics of DNA translocation. Finally, we summarize the common device failures and challenges encountered during fabrication and experiments, explore the causes of these failures, and make suggestions on how to overcome them in the future.

Voltage-Driven Translocation of DNA through a High Throughput Conical Solid-State Nanopore

Nanopores have become an important tool for molecule detection at single molecular level. With the development of fabrication technology, synthesized solid-state membranes are promising candidate substrates in respect of their exceptional robustness and controllable size and shape. Here, a 30–60 (tip-base) nm conical nanopore fabricated in 100 nm thick silicon nitride (Si3N4) membrane by focused ion beam (FIB) has been employed for the analysis of λ-DNA translocations at different voltage biases from 200 to 450 mV. The distributions of translocation time and current blockage, as well as the events frequencies as a function of voltage are investigated. Similar to previously published work, the presence and configurations of λ-DNA molecules are characterized, also, we find that greater applied voltages markedly increase the events rate, and stretch the coiled λ-DNA molecules into linear form. However, compared to 6–30 nm ultrathin solid-state nanopores, a threshold voltage of 181 mV is found to be necessary to drive DNA molecules through the nanopore due to conical shape and length of the pore. The speed is slowed down ∼5 times, while the capture radius is ∼2 fold larger. The results show that the large nanopore in thick membrane with an improved stability and throughput also has the ability to detect the molecules at a single molecular level, as well as slows down the velocity of molecules passing through the pore. This work will provide more motivations for the development of nanopores as a Multi-functional sensor for a wide range of biopolymers and nano materials.

Preparing graphene with notched edges and nanopore defects by γ-ray etching of graphite oxide

Graphene nanostructures with notched edges and nanopore defects were produced by the γ-ray irradiation of the graphite oxide in polar solvents. Because of the grafting of the long polymer chains, the thickness of the graphene monolayers is shown to be significantly increased. In addition, the graphitization degree got increased in unetched regions of the irradiated graphene due to the annealing effect induced by irradiation from the Raman investigation. Spontaneously interlocking between the etching graphene and polymer matrix will be arisen with the formation of these nanostructures. The development of graphene with large contact area and nanopore volume may be of use in composites and sensors.

In situ studies on the shrinkage and expansion of graphene nanopores under electron beam irradiation at temperatures in the range of 400–1200 °C

We report in situ studies on the shrinkage and expansion of graphene nanopores under electron beam irradiation at temperatures of 400–1200°C using a thermal specimen holder in a transmission electron microscope. The shrinkage of nanopores of various sizes is observed. At all temperatures studied in the present work, nanopores with relatively small diameters could be fully closed. And at the low end of our temperature range, 400°C, larger nanopores (those with a diameter of 10nm) could also be closed completely. The nanopore shrinking process can be stopped by blocking the electron beam. We demonstrate an approach for tailoring the size of the graphene nanopore through a combination of electron beam irradiation and controlled heat.

Shale Gas-in-Place Calculations Part I: New Pore-Scale Considerations

SummaryUsing focused-ion-beam (FIB)/scanning-electron-microscope (SEM) imaging technology, a series of 2D and 3D submicroscale investigations revealed a finely dispersed porous organic (kerogen) material embedded within an inorganic matrix. The organic material has pores and capillaries having characteristic lengths typically less than 100 nm. A significant portion of total gas in place appears to be associated with interconnected large nanopores within the organic material.Thermodynamics (phase behavior) of fluids in these pores is quite different; gas residing in a small pore or capillary is rarefied under the influence of organic pore walls and shows a different density profile. This raises serious questions related to gas-in-place calculations: Under reservoir conditions, what fraction of the pore volume of the organic material can be considered available as free gas, and what fraction is taken up by the adsorbed phase? How accurately is the shale-gas storage capacity estimated using the conventional volumetric methods? And finally, do average densities exist for the free and the adsorbed phases?We combine the Langmuir adsorption isotherm with the volumetrics for free gas and formulate a new gas-in-place equation accounting for the pore space taken up by the sorbed phase. The method yields a total-gas-in-place prediction. Molecular dynamics simulations involving methane in small carbon slit-pores of varying size and temperature predict density profiles across the pores and show that (a) the adsorbed methane forms a 0.38-nm monolayer phase and (b) the adsorbed-phase density is 1.8–2.5 times larger than that of bulk methane. These findings could be a more important consideration with larger hydrocarbons and suggest that a significant adjustment is necessary in volume calculations, especially for gas shales high in total organic content. Finally, using typical values for the parameters, calculations show a 10–25% decrease in total gas-storage capacity compared with that using the conventional approach. The role of sorbed gas is more important than previously thought. The new methodology is recommended for estimating shale gas in place.

Magnetic silica spheres with large nanopores for nucleic acid adsorption and cellular uptake

Template assisted fabrication of magnetic silica nanospheres with large nanopores (MSNLP) and their adsorption and delivery of nucleic acids are reported in this paper. Silica spheres with controlled particle diameter (∼400 nm) and large nanopore size (13–24 nm) are prepared by using Brij56 as a template of mesopore, enabling incorporation of magnetic nanocrystals into the particles under mild neutral synthesis conditions. High resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and field-dependent magnetisation measurements confirm that the magnetic nanocrystals have been encapsulated into the silica spheres. The saturation magnetisation values of the resulted magnetic-silica nanocomposites are tunable by adjusting the amount of Fe 3O 4 magnetic nanocrystals used in the synthesis process. The nitrogen sorption analysis reveals that mesopores with large pore size exist in the silica matrix. After functionalisation of the silica surface with poly-( l-lysine) (PLL), the nanoparticles show strong adsorption capacity (q m ranging from 10 to 22.5 μg/mg) for CpG DNA. We have further demonstrated successful delivery of miRNA into rat proximal tubular epithelial cells, facilitated by efficient cellular uptake of the nanocomposites. This work provides a convenient strategy to prepare MSNLP which can offer a versatile platform for biological applications such as simultaneous drug delivery and magnetic resonance imagining under external magnetic field.

Synthesis of mesostructured polyaniline using mixed surfactants, anionic sodium dodecylsulfate and non-ionic polymers and their applications in H2O2 and glucose sensing

Mesostructured polyaniline was prepared by the self-assembly of a mixture of an anionic surfactant, sodium dodecylsulfate and a non-ionic polymeric surfactant (polyethylene glycol, and block-co-polymers such as Pluronic P123 and Brij-35). Materials were characterized by a complementary combination of X-ray diffraction, Scanning electron microscopy, Fourier-transform infrared spectrometer and UV-visible spectrophotometer. Mesostructured polyaniline was used for construction of biosensor, which displayed excellent electrocatalytic response for the detection of H2O2 and glucose compared to conventional polyaniline. The electrocatalytic response observed in the case of mesostructured polyaniline can be correlated with the large surface area and nanopores which enhances the accessibility of H2O2/glucose molecule to the active site that result in high observed current. The methodology adopted in the present study provides a new platform for the fabrication of polyaniline based high-performance glucose and other biosensors.

The Nanopore Inner Sphere Enhancement Effect on Cation Adsorption: Sodium, Potassium, and Calcium

Nanopores in minerals can have a significant impact on cation adsorption, known as the nanopore inner‐sphere enhancement (NISE) effect. Four zeolites representing three size classes of nanoporosity were used in this study to further elucidate the NISE phenomenon and describe its effects on the adsorption of Na, K, and Ca. Sodium and K ions have the same charge, but different ionic diameters. Sodium and Ca ions have similar ionic diameters, but different charges. Adsorption envelopes were created for these three cations on the four zeolites: zeolite Y, ZSM‐5, ferrierite, and mordenite. Comparisons of the magnitudes of the adsorption of Na, K, and Ca on the four zeolites indicated that all cations adsorbed weakly on zeolite Y (large nanopores), Na and K adsorbed strongly on ZSM‐5 and ferrierite (medium nanopores) while Ca adsorbed weakly, and all three cations adsorbed strongly on mordenite (small nanopores). It is noteworthy that in the medium nanopores, the two monovalent cations Na and K adsorbed more strongly than Ca, a divalent cation. The NISE effect is responsible for the changes in the relative strength of each cation's adsorption. This is an unusual adsorption mechanism and is counter to the traditional understanding of ion exchange reactions.