Molecular dynamics simulations of carbon nanotube oscillators deformed by encapsulated copper nanowires

Pure carbon nanotube (CNT) oscillators are compared to the corresponding CNT oscillators encapsulating copper nanowires (Cu@CNTs) by molecular dynamics simulations. The classical oscillation theory provides a fairly good estimate of the mass dependence of the operating frequency when the CNT surface is not deformed by the Cu nanowire. The structural deformations of the CNT induced by the encapsulated copper nanowire have a greater effect on the oscillation frequency than the mass of the copper nanowire. The excess forces of the Cu@CNT oscillator are slightly higher than those of the CNT oscillator and the excess van der Waals forces induced by the inter-wall interactions are 17 times higher than the excess forces induced by the Cu nanowire–CNT interactions.     

Ferritin in the field of nanodevices

Biomineralization of ferritin core has been extended to the artificial synthesis of homogeneous metal complex nanoparticles (NPs) and semiconductor NPs. The inner cavity of apoferritin is an ideal spatially restricted chemical reaction chamber for NP synthesis. The obtained ferritin (biocomplexes, NP and the surrounding protein shell) has attracted great interest among researchers in the field of nanodevices. Ferritins were delivered onto specific substrate locations in a one-by-one manner or a hexagonally close-packed array through ferritin outer surface interactions. After selective elimination of protein shells from the ferritin, bare NPs were left at the positions where they were delivered. The obtained NPs were used as catalysts for carbon nanotube (CNT) growth and metal induced lateral crystallization (MILC), charge storage nodes of floating gate memory, and nanometer-scale etching masks, which could not be performed by other methods.     

Electrochemical behavior of L-cysteine and its detection at carbon nanotube electrode modified with platinum

The electrochemical behavior of L-cysteine (CySH) on platinum (Pt)/carbon nanotube (CNT) electrode was investigated by cyclic voltammetry. CNTs used in this study were grown directly on graphite disk by chemical vapor deposition. Pt was electrochemically deposited on the activated CNT/graphite electrode by electroreduction of Pt(IV) complex ion on the surface of CNTs. Among graphite, CNT/graphite, and Pt/CNT electrodes, improved electrochemical behavior of CySH oxidation was found with Pt/CNT electrode. On the other hand, a sensitive CySH sensor was developed based on Pt/CNT/graphite electrode. A linear calibration curve can be observed in the range of 0.5 microM-0.1 mM. The detection limit of the Pt/CNT electrode is 0.3 microM (signal/nose=3). Effects of pH, scan rate, and interference of other oxidizable amino acids were also investigated and discussed. Additionally, the reproducibility, stability, and applicability of the Pt/CNT electrode were evaluated.     

Carbon Nanotube-Encapsulated Drug Penetration Through the Cell Membrane: An Investigation Based on Steered Molecular Dynamics Simulation

Understanding the penetration mechanisms of carbon nanotube (CNTs)-encapsulated drugs through the phospholipid bilayer cell membrane is an important issue for the development of intracellular drug delivery systems. In the present work, steered molecular dynamics (SMD) simulation was used to explore the possibility of penetration of a polar drug, paclitaxel (PTX), encapsulated inside the CNT, through a dipalmitoylphosphatidylcholine bilayer membrane. The interactions between PTX and CNT and between PTX and the confined water molecules inside the CNT had a significant effect on the penetration process of PTX. The results reveal that the presence of a PTX molecule increases the magnitude of the pulling force. The effect of pulling velocity on the penetration mechanism was also investigated by a series of SMD simulations, and it is shown that the pulling velocity had a significant effect on pulling force and the interaction between lipid bilayer and drug molecule.     

Tungsten–Carbon Nanotube Composite Photonic Crystals as Thermally Stable Spectral‐Selective Absorbers and Emitters for Thermophotovoltaics

Thermophotovoltaics (TPVs) is a promising energy conversion technology which can harvest wide‐spectrum thermal radiation. However, the manufacturing complexity and thermal instability of the nanophotonic absorber and emitter, which are key components of TPV devices, significantly limit their scalability and practical deployment. Here, tungsten–carbon nanotube (W‐CNT) composite photonic crystals (PhCs) exhibiting outstanding spectral and angular selectivity of photon absorbance and thermal emission are presented. The W‐CNT PhCs are fabricated by nanoscale holographic interferometry‐based patterning of a thin‐film catalyst, modulated chemical vapor deposition synthesis of high‐density CNT forest nanostructures, and infiltration of the CNT forests with tungsten via atomic layer deposition. Owing to their highly stable structure and composition, the W‐CNT PhCs exhibit negligible degradation of optical properties after annealing for 168 hours at 1273 K, which exceeds all previously reported high‐temperature PhCs. Using the measured spectral properties of the W‐CNT PhCs, the system efficiency of a GaSb‐based solar TPV (STPV) that surpasses the Shockley–Queisser efficiency limit at modest operating temperatures and input powers is numerically predicted. These findings encourage further practical development of STPVs, and this scalable fabrication method for composite nanostructures could find other applications in electromagnetic metamaterials.     

Comparative prediction of binding affinity of Hydroxyurea anti-cancer to boron nitride and carbon nanotubes as smart targeted drug delivery vehicles

Abstract

In this study, the adsorption of Hydroxyurea (HU) onto the inner and outer surfaces of boron nitride and carbon nanotubes (CNTs) was investigated using the density functional theory calculations and molecular dynamics (MDs) simulations in aqueous solution. The values of the adsorption energy show that HU molecule is preferentially adsorbed inside of boron nitride and CNTs with the molecular axis parallel to the tubes axis, which means that the cavity of nanotubes is favorable for encapsulation of this drug. Also, it was found that the HU/boron nitride nanotube (BNNT) system is more stable than the HU/CNT system. The stability of the complexes of HU/ BNNT attributed to the formation of the intermolecular hydrogen bonds between the H atoms of HU molecule and the N atoms of BNNT, which is confirmed by Bader’s quantum theory of atoms in molecules. The natural bond orbital analysis shows the charge transfers occur from HU molecule to nanotubes in all complexes. Moreover, the adsorption of HU molecule on the surfaces of the nanotubes was investigated by explicit water models. Also, the adsorption behavior of HU on the functionalized boron nitride and CNTs is investigated to design and develop new nanocarriers for biomedical applications. Furthermore, MDs simulations are examined in the presence of one and two drug molecules. The obtained results illustrate that the lowest value of Lennard–Jones (L–J) energy between drug and nanotubes exist in the simulation system with two drug molecules.     

The influence of nicotine on pioglitazone encapsulation into carbon nanotube: the investigation of molecular dynamic and density functional theory

In this work, molecular dynamics simulations of the insertion of pioglitazone into the nanotube with chirality (10, 10) at 400 K and 1 bar in the presence and absence of nicotine molecules and in different drug concentrations have been studied. The main aim is consideration of the effect of nicotine in the drug encapsulation process. The results indicate that encapsulation of pioglitazone could be attributed to the water flow via van der Waals and hydrophilic interactions. Because of the existence of the partial π–π interactions between aromatic rings of pioglitazone and the conjugated aromatic rings of nanotube, pioglitazone molecule can enter inside the nanotube. Some physical properties such as hydrogen bonding, number of contacts, also, the diffusion coefficient of the pioglitazone and water molecules, and variation of the center of mass have been calculated during the simulation. Furthermore, computing the electronic structure has also been done on model systems for quantitative determination of the adsorption energy (E_ads). The B3LYP/6-31G* level calculations on four different configurations of pioglitazone/carbon nanotube (CNT) and nicotine/CNT show that the interaction of drug with the inside of the nanotube is stronger than the other forms.     

Noncovalent and covalent functionalization of a (5, 0) single-walled carbon nanotube with alanine and alanine radicals

We have systematically investigated the noncovalent and covalent adsorption of alanine and alanine radicals, respectively, onto a (5, 0) single-walled carbon nanotube using first-principles calculation. It was found that XH···π (X = N, O, C) interactions play a crucial role in the non-ovalent adsorption and that the functional group close to the carbon nanotube exhibits a significant influence on the binding strength. Noncovalent functionalization of the carbon nanotube with alanine enhances the conductivity of the metallic (5, 0) nanotube. In the covalent adsorption of each alanine radical onto a carbon nanotube, the binding energy depends on the adsorption site on CNT and the electronegative atom that binds with the CNT. The strongest complex is formed when the alanine radical interacts with a (5, 0) carbon nanotube through the amine group. In some cases, the covalent interaction of the alanine radical introduces a half-filled band at the Fermi level due to the local sp ³ hybridization, which modifies the conductivity of the tube.     

Giant and flux controllable pumping of water molecules in a double-walled carbon nanotube

We designed a water pumping system based on double-walled carbon nanotube. In this system, the inner tube was fixed as the water channel, while the exterior was moved similarly to the piston motion along the axial direction to induce pumping force. Molecular dynamics simulations confirmed that the water flux is sensitive to the motion velocity of the outer tube so that giant and controllable unidirectional water flow can be achieved in this system by varying the velocity. The enhancement of the pumping ability mainly results from the carbon–water van der Waals driving forces of the exterior tube and the osmosis pressure of the water reservoir. This design may open a new way for water pumping in the field of nanodevices.     

Anatomy of the renal pelvis in the hamster.

The hamster renal pelvis has been studied by means of low-power light microscopy, scanning electron microscopy and morphometric analyses. The results of this study are highly suggestive that the contact of pelvic urine with the other medulla as well as with the inner medulla may be an important aspect of final urine formation. The outer medulla constituted nearly 50% of the total pelvic surface area, with the inner stripe of the outer medulla more than twice the pelvic surface area of the outer stripe of the outer medulla. The large outer medullary pelvic surface area was accounted for by the elaboration of the upper pelvic walls into peripelvic columns, opercula ("secondary pyramids"), fornices and secondary pouches. A thin simple-squamous to low cuboidal pelvic epithelium separated pelvic urine from outer medullary parenchyma. The inner medulla which constituted about one quarter of the total pelvic surface area was covered by a cuboidal to columnar pelvic epithelium which appeared morphologically similar to the papillary collecting duct epithelium. Tubules and capillaries of the inner medulla did not appear as closely juxtaposed to the pelvic epithelium as did those of the outer medulla. Cortical tissue comprised only 11.7% of the total pelvic surface area and was covered by transitional epithelium similar to that of ureter and bladder. The previously reported impermeability of this epithelium suggests that pelvic urine contact with the cortex is unimportant in final urine formation. The rich layer of smooth muscle under the transitional epithelium probably functions to move urine into and out of the pelvis during pelvic peristalsis, which has been observed in vivo.     

下挖式日光温室土墙温度和热流的变化规律

2011年12月-2012年3月,在山东寿光对下挖式日光温室土质后墙不同厚度层的温度、热流进行连续测试,分析了下挖式日光温室土墙温度和热流的变化规律,确定了土墙的合理厚度.结果表明: 冬季,研究区温室墙体内侧表面、外侧覆盖层表面温度、热流的变化幅度较大,且与室内外气温的变化趋势相同.墙体温度总体上由内侧表面到外侧表面呈不断降低的趋势,墙体内侧温度、热流变化幅度较大的层次多于外侧.墙体温度、热流的变化幅度从浅层到深层依次减小.连阴天条件下,墙体内侧各层温度都有不同程度的下降,向室内放热的层次不断加深,而外侧各层次以向室外放热为主.根据墙体温度和热流的变化规律,在墙体外侧有覆盖层的情况下,把墙体从内到外划分为蓄热层、过渡层和御冷层,其厚度分别为0.8～1.0 m、2.2～2.6 m和0.4～0.6 m.在不考虑过渡层的条件下,寿光日光温室土墙厚度以1.4～1.6 m为宜.     

Molecular dynamics simulation studies of mechanical properties of different carbon nanotube systems

Various mechanical properties of single-walled carbon nanotubes (SWCNT) and double-walled carbon nanotubes (DWCNT) are evaluated using molecular dynamics (MD) simulations. A tensioning process was first performed on a SWCNT whose interaction is based on the Brenner’s ‘second generation’ potential under varying length–diameter ratios and strain rates, in order to understand the SWCNT’s behaviour under axial tension. The results showed an increase in the SWCNT’s ultimate tensile strength and a decrease in critical strain given the conditions of increasing strain rate and a decreasing length–diameter ratio. Comparison was done with previous studies on axial tensioning of SWCNT to validate the results obtained from the set-up, based on the general stress–strain relationship and key mechanical properties such as the strain at failure and the Young’s modulus. A DWCNT was then constructed, and Lennard-Jones ‘12-6’ potential was used to describe the energy present between the nanotube layers. Extraction of the inner tube in a DWCNT was performed using two inner wall tubings of different diameters to draw comparison to the energies needed to separate fully the outer and inner tubing. Finally, a bending test was performed on two DWCNTs with different intertube separations. Insights into the entire bending process were obtained through analyses of the variations in the strain energy characteristic of the surface atoms near the bending site, as the DWCNT is gradually bent until failure.     

A comparative study on carbon, boron-nitride, boron-phosphide and silicon-carbide nanotubes based on surface electrostatic potentials and average local ionization energies

A density functional theory study was carried out to predict the electrostatic potentials as well as average local ionization energies on both the outer and the inner surfaces of carbon, boron-nitride (BN), boron-phosphide (BP) and silicon-carbide (SiC) single-walled nanotubes. For each nanotube, the effect of tube radius on the surface potentials and calculated average local ionization energies was investigated. It is found that SiC and BN nanotubes have much stronger and more variable surface potentials than do carbon and BP nanotubes. For the SiC, BN and BP nanotubes, there are characteristic patterns of positive and negative sites on the outer lateral surfaces. On the other hand, a general feature of all of the systems studied is that stronger potentials are associated with regions of higher curvature. According to the evaluated surface electrostatic potentials, it is concluded that, for the narrowest tubes, the water solubility of BN tubes is slightly greater than that of SiC followed by carbon and BP nanotubes.

Molecular dynamics simulation of doxorubicin adsorption on a bundle of functionalized CNT

In this study, molecular dynamics simulation is used to investigate the adsorption of an anticancer drug, doxorubicin, on bundles of functionalized single-walled carbon nanotubes (SWNTs) in an aqueous solution. Carboxylic group has been selected as the functional group. Molecular dynamics (MD) simulations are performed for both separated systems containing a SWNT bundle and a functionalized carbon nanotube bundle, and results are compared with existing experimental data. MD results show that doxorubicin can be adsorbed on CNTs using different methods such as entrapment within CNT bundle, attachment to the side wall of the CNT, and adsorption on the CNT inner cavity. For functionalized CNT, the adsorption of drugs on the functional groups is essential for predicting the enhancement of drug loading on the functionalized nanotubes. Furthermore, the adsorption behavior of doxorubicin on CNTs is fitted with Langmuir and Freundlich isotherm models. The results show that Langmuir model can predict the adsorption behavior of doxorubicin on CNTs more accurately than Freundlich model does. As predicted by this isotherm model, the adsorption process of doxorubicin on CNTs is relatively difficult, but it can be improved by increasing the functional groups on the CNTs surface.     

Glucose sensors made of novel carbon nanotube-gold nanoparticle composites

Carbon nanotube and metal particle composites have been exploited to fabricate high performance electrochemical devices. However, the physical and chemical procedures to synthesize the composites are labor intensive and inefficient. Our study reveals an one-step wet chemistry method to accomplish fast and controllable production of gold nanoparticle (AuNP) and carbon naotube (CNT) composites. Such a process is sensitive to the surface charge. Especially, when functionalized with carboxyl groups, the CNTs carried negative charges and showed low level association with negatively charged AuNPs. Thermal treatment was employed to decompose the carboxyl groups and render each CNT a charge-free surface thereby achieving a high level AuNP-CNT association. The fabricated glucose sensors demonstrated dependence of their sensitivities to the amount of AuNPs on the CNTs. The enhancement of sensitivity can be attributed to an accelerated electron transfer rate from glucose oxidase Gox to the electrode. The Michaelis-Menten kinetics also indicated improved performance in the glucose sensor made of AuNP-CNTs. Therefore, our research revealed a novel approach to produce metallic nanoparticle and CNT composite for fabricating high performance electrochemical sensors.     

Interaction of coupled nonlinear oscillators having different intrinsic resting levels

The interaction among coupled oscillators is governed by oscillator properties (intrinsic frequency and amplitude) and coupling mechanisms. This study considers another oscillator property, the intrinsic resting level, and evaluates its role in governing oscillator interactions. The results of computer experiments on a chain of either three or five bidirectionally coupled nonlinear oscillators, suggest that an intrinsic resting level gradient, if present, is one of the factors governing the interaction between coupled oscillators. If there is no intrinsic frequency gradient, then an intrinsic resting level gradient is sufficient to produce many features of interaction among coupled oscillators. If both intrinsic frequency and intrinsic resting level gradients are present, then both of them determine the manner in which the coupled oscillators interact with each other.     

Tethered lipid bilayers on electrolessly deposited gold for bioelectronic applications

This paper presents the formation of a novel biomimetic interface consisting of an electrolessly deposited gold film overlaid with a tethered bilayer lipid membrane (tBLM). Self-assembly of colloidal gold particles was used to create an electrolessly deposited gold film on a glass slide. The properties of the film were characterized using field-effect scanning electron microscopy, energy dispersive spectroscopy, and atomic force microscopy. Bilayer lipid membranes were then tethered to the gold film by first depositing an inner molecular leaflet using a mixture of 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-[3-(2-pyridyldithio)propionate], 1,2-di-O-phytanyl-sn-glycero-3-phosphoethanolamine (DPGP), and cystamine in ethanol onto a freshly prepared electrolessly deposited gold surface. The outer leaflet was then formed by the fusion of liposomes made from DPGP or 1,2-dioleoyl-sn-glycero-3-phosphocholine on the inner leaflet. To provide functionality, two membrane biomolecules were also incorporated into the tBLMs: the ionophore valinomycin and a segment of neuropathy target esterase containing the esterase domain. Electrochemical impedance spectroscopy, UV/visible spectroscopy, and fluorescence recovery after pattern photobleaching were used to characterize the resulting biomimetic interfaces and confirm the biomolecule activity of the membrane. Microcontact printing was used to form arrays of electrolessly deposited gold patterns on glass slides. Subsequent deposition of lipids yielded arrays of tBLMs. This approach can be extended to form functional biomimetic interfaces on a wide range of inexpensive materials, including plastics. Potential applications include high-throughput screening of drugs and chemicals that interact with cell membranes and for probing, and possibly controlling, interactions between living cells and synthetic membranes. In addition, the gold electrode provides the possibility of electrochemical applications, including biocatalysis, bio-fuel cells, and biosensors.     

Grafting of molecularly imprinted polymers on iniferter-modified carbon nanotube

Molecularly imprinted polymers (MIPs) were grafted on iniferter-modified carbon nanotube (CNT). Tween 20 was first immobilized on CNT by hydrophobic interactions. The hydroxyl-functionalized CNT was modified by silanisation with 3-chloropropyl trimethoxysilane. The iniferter groups were then introduced by reacting the CNT-bound chloropropyl groups with sodium N,N-diethyldithiocarbamate. UV light-initiated copolymerization of ethylene glycol dimethacrylate (crosslinking agent) and methacrylic acid (functional monomer) resulted in grafting of MIP on CNT for theophylline as a model template. MIPs grafted on CNT were characterized with elemental analysis, scanning electron microscopy, and thermogravimetric analysis. The theophylline-imprinted polymer on CNT showed higher binding capacity for theophylline than non-imprinted polymer on CNT and selectivity for theophylline over caffeine and theobromine (similar structure molecules). The data of theophylline and caffeine binding into the theophylline-imprinted polymer correlated well with the Scatchard plot. These MIPs on CNT can potentially be applied to probe materials in biosensor system based on CNT field effect transistor.     

Effect of the addition mode of carbon nanotubes for the production of chitosan hydrogel core-shell beads on adsorption of Congo red from aqueous solution

The adsorption performance of chitosan (CS) hydrogel beads (CSBs) generated by sodium dodecyl sulfate (SDS) gelation with multi-walled carbon nanotube (CNT) impregnation was investigated for Congo red removal as a model anionic dye. CNT-impregnated CSBs were prepared by four different strategies for dispersing CNTs: (a) in CS solution (CSBN1), (b) in SDS solution (CSBN2), (c) in CS solution containing cetyltrimethylammonium bromide (CTAB) (CSBN3), and (d) in SDS solution for gelation with CTAB-containing CS solution (CSBN4). It was observed from FE-SEM study that depending on nature of CNT dispersion, CNTs were found on the outer surface of CSBN2 and CSBN4 only. The adsorption capacity of the CSBs varied with the strategy used for CNT impregnation, and CSBN4 exhibited the highest maximum adsorption capacity (375.94 mg/g) from the Sips model. The lowest Sips maximum adsorption capacity by CSBN3 (121.07 mg/g) suggested significant blocking of binding sites of CS by CNT impregnation.     

A High‐Efficiency Sulfur/Carbon Composite Based on 3D Graphene Nanosheet@Carbon Nanotube Matrix as Cathode for Lithium–Sulfur Battery

Carbon materials have attracted extensive attention as the host materials of sulfur for lithium–sulfur battery, especially those with 3D architectural structure. Here, a novel 3D graphene nanosheet–carbon nanotube (GN–CNT) matrix is obtained through a simple one‐pot pyrolysis process. The length and density of CNTs can be readily tuned by altering the additive amount of carbon source (urea). Specifically, CNTs are in situ introduced onto the surface of the graphene nanosheets (GN) and show a stable covalent interaction with GN. Besides, in the GN–CNT matrix, cobalt nanoparticles with different diameters exist as being wrapped in the top of CNTs or scattering on the GN surface, and abundant heteroatoms (N, O) are detected, both of which can help in immobilizing sulfur species. Such a rationally designed 3D GN–CNT matrix makes much more sense in enhancing the electrochemical performance of the sulfur cathode for rapid charge transfer and favorable electrolyte infiltration. Moreover, the presence of dispersed cobalt nanoparticles is beneficial for trapping lithium polysulfides by strong chemical interaction, and facilitating the mutual transformation between the high‐order polysulfides and low‐order ones. As a result, the S/GN–CNT composite presents a high sulfur utilization and large capacity on the basis of the S/GN–CNT composite as active material.