TEM study of chirality in MoS2 nanotubes

The dark-field diffraction contrast of helical nanotubes (NTs) is shown to be asymmetric when an NT is tilted at appropriate angle with respect to the incident electron beam. This phenomenon was used for the chirality determination of multi-shell NTs observed in MoS₂ layered compound. Both kinds of NT — helical and non-helical — were found. In the case of helical NTs only right-hand chirality was observed.     

Application of mixed self-assembled monolayers (Mixed SAMs) for nucleic acid detection

Mixed self-assembled monolayers (Mixed SAMs) consisting of 8-Ferrocenyl-1-octanethiol and 6-Mercapto-1-hexanol (FcOT:MCH) with probe PNA on gold electrodes were fabricated by using two-step after the optimization of immobilization temperature of FcOT:MCH SAMs. Using AC voltammetry, a novel nucleic acid detection platform, with mixed SAMs, was proposed. A negative formal potential shift was observed after complementary ssDNA hybridization while there was no significant difference after non-complementary ssDNA hybridization. Compatible results were obtained with the measurement of formal potential differences between mixed SAMs and target DNA (complementary and non-complementary DNA) in different target DNA concentrations. The formal potential difference between mixed SAMs immobilization and complementary ssDNA hybridization was measured in different ionic strength concentrations.     

Immobilization of DNA on 11-mercaptoundecanoic acid-modified gold (111) surface for atomic force microscopy imaging

Immobilized DNA on preformed 11-mercaptoundecanoic acids (MUDA) self-assembled monolayers (SAMs) on a gold (111) surface was bound by a divalent cation bridges was imaged by atomic force microscopy (AFM). The DNA immobilization was attributed to the formation of ionic bridges between the carboxylate groups of MUDA and the phosphate groups of DNA. AFM images revealed that DNA molecules could be immobilized strongly enough to permit stable and reproducible imaging. The effect of different bridge cations, such as Mg(2+), Zn(2+) and Cu(2+), and the pH of DNA assembled solution on immobilization and conformation of DNA was studied. Plasmid DNA pBR 322/Pst I molecules were straightened by using a molecular combing technique on the MUDA surface.     

Electrochemical DNA biosensor with nanometer scale using nano-patterning lithography machine

Major challenges in the field of electrochemical DNA hybridization biosensors are the immobilization of DNA and the detection of hybridization signals. The method of DNA immobilization using the nano-patterning machine and detection for DNA hybridization signals has been proposed. Here, two gold electrodes were deposited on SiO₂ layer and the gap between the electrodes was fabricated by electron beam lithography. 3-aminopropyltriethoxysilane (APTES) solution was selectively treated to immobilize the amino-modified oligonucleotides onto the SiO₂ layer between the electrodes. The recognition of DNA hybridization was accomplished by metallic aggregation of nano-particles. The results showed that DNA is immobilized with nanometer scales and the method for detecting hybridization signals is useful. The experimental results were verified by I-V curves. The conductance between two electrodes changed with the density of the Au-nanoparticles immobilized onto the oxide layer. These results can be applied to the DNA chip and the multi-functional sensors which will be researched in the further study.     

MULTI-WALL CARBON NANOTUBE-BASED DNA NANOSENSOR FOR DETERMINING MITOXANTRONE-DNA INTERACTION IN-VITRO

The present study involves the development of a carbon nanotube based DNA nanosensor to determine the toxicological behavior of mitoxantrone (MTX). Mitoxantrone intercalates with DNA and produces a MTX-DNA adduct, resulting in the blockade of protein synthesis and excessive production of free radicals in the myocardium which eventually leads to cardiac toxicity. So, our work employs a DNA nanosensor to investigate the interaction of MTX with DNA. Multi-wall carbon nanotubes (MWCNTs) were functionalized with carboxyl group and were used for immobilization of DNA to construct the DNA nanosensor. The DNA nanosensor was immersed in MTX solution to monitor MTX-DNA interaction with respect to time and alter the resistance of the nanosensor. It was observed that MTX-DNA interaction is fast initially and as time elapses, the change in interaction gets slow due to formation of MTX-DNA adduct. The limit of detection (LOD) and limit of quantification (LOQ) were found as 150 (ng/mL) and 456 (ng/mL), respectively, for DNA nanosensor. This study suggests that the potentiometric nanosensor allows real-time monitoring of the drug-DNA interaction changes by measuring the potential at DNA/sensor interface which can prove to be an important tool in drug discovery pipelines and molecular toxicology.     

Role of nanofiller in friction of polymers based on polycaproamide: Indirect effect

The effect of nanofillers (multiwalled carbon nanotubes) on the tribological behavior of polycaproamide is studied when introduced into the polymer by polymerization filling. The introduction of insignificant quantities (∼0.1 wt %) of nanotubes provides their homogeneous distribution in the polymer and contributes to reducing the wear and friction coefficient. This is mainly due to the role of nanotubes as nucleators of the fine spherulitic polycaproamide structure. Such an indirect effect of the nanofiller on the polymer’s tribological behavior is seen when nanotubes are added to the melt in the course of granulation of polycaproamide compositions reinforced by carbon fibers, the effect of nanotubes being reduced with increasing amount of the reinforcing filler.     

Detection of C-reactive protein on a functional poly(thiophene) self-assembled monolayer using surface plasmon resonance

The preparation of a new poly(thiophene) with pendant N-hydroxysuccinimide ester groups and its application to immobilization of biomolecules are reported. A thiophene derivative of N-hydroxysuccinimide ester was polymerized with FeCl(3) in chloroform and the resulting poly(thiophene) was characterized by nuclear magnetic resonance (NMR), Fourier transform infrared (FT-IR), and gel permeation chromatography (GPC). This polymer reacts with amine-bearing molecules to yield new poly(thiophene) derivatives and the specific interactions at the side groups could be detected. Thus, a self-assembled monolayer (SAM) using the polymer was formed on a gold-coated quartz cell and anti-C-reactive protein (anti-CRP) was immobilized. The binding behavior of CRP on the surface was monitored by use of a surface plasmon resonance (SPR) sensor system.     

核酸适配体在酶固定化研究中的应用

本研究基于核酸适配体对胰蛋白酶的高特异性和高亲和力,通过在硅胶颗粒上固定核酸适配体,从而实现胰蛋白酶的间接固定,并以牛血清白蛋白（BSA）为研究对象,对固定化胰蛋白酶的酶解活性进行表征。结果表明,这种酶固定化方法对酶的活性几乎没有影响。与传统的固定方法相比,这种酶固定化方法在保证胰蛋白酶活性的基础上,也可以实现胰蛋白酶的洗脱和重新固载,达到固载基质重新利用的目的,为酶的固定化提供了一种新的研究思路。     

Fabrication of self-assembled oligophenylethynylenethiol monolayer for electrochemical glucose biosensor

An electrochemical glucose biosensor was developed using a gold (Au) electrode, which was composed of self-assembled oligophenylethynylenethiol monolayer and glucose oxidase (GOx) structure. Oligophenylethynylenethiol was used as a chemical linker for the immobilization of GOx on Au electrode, which facilitates the transfer of electron produced by enzyme reaction to the Au electrode. The electrical property of self-assembled oligophenylethynylenethiol monolayer was investigated by using cyclic voltammetry (CV). The formation of self-assembled oligophenylethynylenethiol monolayer and GOx layer on Au surface was verified by using atomic force microscopy (AFM) and surface plasmon resonance (SPR). The electrochemical glucose biosensor exhibited a linear relationship between target concentration and oxidation current in the range of 2–30 mM and its detection limit was 2 mM.     

多壁碳纳米管净化-超高效液相色谱-串联质谱技术同时测定牛奶中青霉素类药物残留

研究了多壁碳纳米管净化-超高效液相色谱-串联质谱技术同时测定牛奶中的羟氨苄青霉素、青霉素V、氨苄青霉素、苯咪青霉素、甲氧苯青霉素、青霉素G、苯咪青霉素、邻氯青霉素、乙氧萘青霉素和双氯青霉素药物残留。样品用乙腈沉淀蛋白,提取液用磷酸缓冲液稀释后,经改性的多壁碳纳米管材料净化,通过Waters C18色谱柱分离,以乙腈和10 mmol/L乙酸铵（pH 4.5）溶液为流动相进行梯度洗脱,采用电喷雾-正离子多反应监测模式检测,内标法定量。10种青霉素药物在相应浓度范围内的线性相关系数均大于0.99,方法的定量限在0.1～10.0 μg/kg之间。在低、中、高3个浓度添加水平下,10种青霉素药物的平均回收率为72.0%～110%,相对标准偏差在1.83%～9.33%之间。多壁碳纳米管材料具有较好的净化效果,该方法可以快速、准确地测定牛奶中的青霉素类药物残留。     

Investigations on the strength of mechanical joints prepared from carbon fiber laminates with addition of carbon nanotubes

The present work is to examine the failure modes and failure loads in pin joints prepared from carbon/epoxy composite laminates with addition of multiwalled carbon nanotubes (MWCNT) as nanofillers. The effect of MWCNT in the carbon/epoxy composites was studied by adding 0.1 to 0.5 wt.% content in the epoxy resin. The maximum tensile strength was observed upto 0.3 wt.%, which is due to the enhanced interfacial bond strength and the efficient stress transfer between the stiff MWCNT and soft polymer matrix through refined polymer/MWCNT interface. The nanocomposite laminates for pin joints were prepared using optimised 0.3 wt.% of MWCNT. The different geometric combinations of width to diameter (W/D) and edge to diameter (E/D) ratios were varied from 2 to 5, respectively. The numerical analysis was performed using Hashin damage criteria along with progressive damage analysis to compare the predicted failure loads with the experimental results.     

Preparation and characterization of single-walled carbon nanotube/nylon 6, 6 nanocomposites

Morphological, thermal, mechanical, and solvent uptake was characterized for neat nylon 6, 6 and functionalized single-walled carbon nanotube/nylon 6, 6. Single-walled carbon nanotubes were functionalized by acid which introduced carboxyl groups on the nanotubes. Scanning electron micrographs of the fractured surfaces of the nanocomposites suggested that the functionalized single-walled carbon nanotubes were dispersed and embedded within the nylon 6, 6 polymer matrix. Polarized optical micrographs showed that the size of spherulites of the nanocomposites decreased, which may be due to nucleation of the carbon nanotubes. Thermogravimetric analysis showed that the stability of the functionalized single-walled carbon nanotubes/nylon 6, 6 nanocomposites was higher by 28–35°C than neat nylon 6, 6. The uptake of solvent by the functionalized single-walled carbon nanotube/nylon 6, 6 was lower than the neat nylon 6, 6, which may be due to the hydrophobic nature of functionalized single-walled carbon nanotubes and their interaction with the polymer.     

Immobilization and stretching of 5′‐pyrene‐terminated DNA on carbon film deposited on electron microscope grid

The immobilization and stretching of randomly coiled DNA molecules on hydrophobic carbon film is a challenging microscopic technique, which possess various applications, especially for genome sequencing. In this report the pyrenyl nucleus is used as an anchor moiety to acquire higher affinity of double stranded DNA to the graphite surface. DNA and pyrene are joined through a linker composed of four aliphatic methylene groups. For the preparation of pyrene‐terminated DNA a multifunctional phosphoramidite monomer compound was designed. It contains pyrenylbutoxy group as an anchor moiety for π‐stacking attachment to the carbon film, 2‐cyanoethyloxy, and diisopropylamino as coupling groups for conjugation to activated oligonucleotide chain or DNA molecule. This monomer derivative was suitable for incorporation into automated solid‐phase DNA synthesis and was attached to the 5′ terminus of the DNA chain through a phosphodiester linkage. The successful immobilization and stretching of pyrene‐terminated DNA was demonstrated by conventional 100 kV transmission electron microscope. The microscopic analysis confirmed the stretched shape of the negatively charged nucleic acid pieces on the hydrophobic carbon film. Microsc. Res. Tech. 78:994–1000, 2015. © 2015 Wiley Periodicals, Inc.     

Free vibration analysis of functionally graded CNT-reinforced nanocomposite beam using Eshelby-Mori-Tanaka approach

This work deals with the effect of agglomeration and distribution of carbon nanotube on the free vibration characteristics of a functionally graded nanocomposite beams reinforced by single-walled carbon nanotubes (SWCNTs) by employing an equivalent fiber based on the Eshelby-Mori-Tanaka approach. Different SWCNTs distributions in the thickness directions are introduced to improve fundamental natural frequency of polymer composite beam. The micromechanics models used in the study include a two parameter model of agglomeration. An embedded carbon nanotube in a polymer matrix and its surrounding inter-phase is replaced with an equivalent fiber for predicting the mechanical properties of the carbon nanotube/polymer composite. The system of equations of motion is derived by using the principle of virtual work under the assumptions of the Euler-Bernoulli beam theory. The finite element method is employed to obtain a numerical approximation of the motion equation. Numerical results are presented in both tabular and graphical forms to figure out the effects of nanotube agglomeration, CNTs distribution and boundary conditions on the dynamic characteristics of the beam. The above mentioned effects play very important role on the dynamic behavior of the beam.     

New polyacrylamide gel-based methods of sample preparation for optical microscopy: immobilization of DNA molecules for optical mapping

New methods have been developed for rapid immobilization of biological macromolecules and other microscopic objects from aqueous solution at gel/gel, gel/solid and gel/solution interfaces using thin polyacrylamide gels covalently bound to glass surfaces. When quickly spread over a dry gel, an aqueous sample loses most of its water and low-molecular-weight solutes due to migration of these components into the gel. All optically observable objects thus become concentrated at the gel surface and may be easily located by light microscopy. Based on this, a procedure for binding DNA at a positively charged gel/solution interface was developed. A mild immobilization of the DNA molecules was obtained, allowing 'all in focus' observations of DNA digestion by restriction endonucleases with an apparent rate close to that in solution.     

An engineered microenvironment for multidimensional microscopy of live cells

Multidimensional imaging (MD) of live cells is gaining importance in biomedical research as the commercial availability of confocal, nonlinear optical microscopes, environmental chambers, and specific fluorescence probes grows. One crucial aspect of the MD live cell imaging involves the proper immobilization of cells, which refers to the rapid and sufficient immobilization of cells on the microscope stage, neither disrupting the cellular structure and functions nor affecting the optical properties of the cells and the environments. Conventional cell immobilization methods glue the anchoring cells to coated surfaces, but such methods require centrifugation or extended incubation and are not suitable for cells in suspension. Most of the current three-dimensional (3-D) gels either exhibit unsatisfactory optical properties or have adverse effects on cell functions in culture. Recently, an engineered 3-D microcapsule has been developed that involves the complex coacervation of a positively charged collagen and a negatively charged polymer of 2-hydroxyethyl methacrylate--methacrylic acid--methyl methacrylate (HEMA-MMA-MAA). Hence, confocal imaging of live cells in this engineered 3-D microenvironment was investigated for its optical properties and cellular function compatibility. We report here that this microenvironment facilitates efficient cell immobilization, exhibits good optical properties, and can preserve cellular structures and functions, which will be useful in MD imaging of live cells for various applications.     

Process optimization for PA12/MWCNT nanocomposite manufacturing by selective laser sintering

Nanocomposites produced through the addition of carbon nanotubes to a polymeric matrix can improve the material properties. The mobility of the polymer chains is usually affected, and this is also related to the properties. Parts produced with the free-form fabrication process using the selective laser sintering (SLS) technique can be used in different high-performance applications as they do not require expensive tools for their manufacture. A specific field of interest is the aerospace industry which is characterized by a low production volume and the need for materials with a high performance to weight ratio. In this study, the free-form fabrication by SLS of parts made from nanocomposites comprised of polyamide 12 and multiwalled carbon nanotubes (MWCNTs) was investigated. Specimens were manufactured by SLS to identify the appropriate processing parameters to achieve high mechanical properties for aerospace applications. Laser energy density was adjusted to improve the material density, flexural modulus, and stress at 10 % elongation. Design of experiments was used to identify and quantify the effects of various factors on the mechanical properties. The results obtained showed that there was a limit to the amount of MWCNTs which could be mixed with the polyamide powder to improve the mechanical properties since a higher content affected the laser sintering process.     

New Single-Walled Carbon Nanotubes–Ionic Liquid Lubricant. Application to Polycarbonate–Stainless Steel Sliding Contact

Single-walled carbon nanotubes (NTs) were added in a 0.5 wt% proportion to the room temperature ionic liquid (IL) 1-octyl, 3-methylimidazolium chloride ([OMIM]Cl). The [OMIM]Cl + NT mixtures obtained by mechanical grinding in an agate mortar ([OMIM]Cl + NT(g)) or by mechanical grinding and ultrasound dispersion ([OMIM]Cl + NT(g + us)) were used as lubricants of the polycarbonate (PC) disc/AISI 316L stainless steel pin contact. When the [OMIM]Cl + NT(g + us) dispersion is used, a negligible wear rate and a friction coefficient reduction of a 66% with respect to neat IL, and of a 50% with respect to [OMIM]Cl + NT(g), is achieved. Results are discussed on the basis of DSC, TGA, Raman spectroscopy, TEM microscopy, XRD, XPS and surface topography analysis.     

Labelling quality and chromosome morphology after low temperature FISH analysed by scanning far-field and near-field optical microscopy

A non‐enzymatic, low temperature fluorescence in situ hybridization (LTFISH) procedure was applied to metaphase spreads and interphase cell nuclei. In this context ‘low temperature’ means that the denaturation procedure of the chromosomal target DNA usually applied by heat treatment and chaotropic agents such as formamide was completely omitted so that the complete hybridization reaction took place at 37 °C. For LTFISH, the DNA probe had to be single‐stranded, which was achieved by means of separate thermal denaturation of the DNA probe only. The DNA probe pUC1.77 was used for all LTFISH experiments. The labelling quality (number of binding sites, relative background intensity, relative intensity of major and minor binding sites) was analysed by confocal laser scanning microscopy (CLSM). An optimum in specificity and signal quality was obtained for 15 h hybridization time. For this hybridization condition of LTFISH, the chromosomal morphology was analysed by scanning near‐field optical microscopy (SNOM). The results were compared with the morphology of chromosomes after (a) labelling of all centromeres using the same chemical treatment in the FISH procedure but with the application of target denaturation, and (b) labelling of all centromeres using a standard FISH protocol including thermal denaturation of the DNA probe and the chromosomal target. Depending on the FISH‐procedure applied, SNOM images show substantial differences in the chromosome morphology. After LTFISH the chromosome morphology appeared to be much better preserved than after standard FISH. In contrast, the application of the LTFISH chemical treatment accompanied by heat denaturation had a very destructive influence on chromosomal morphology. The results indicate that, at least for certain DNA probes, specific chromosome labelling can be obtained without the usually applied heat and chemical denaturation of the DNA target, resulting in an apparently well preserved chromatin morphology as visualized by SNOM. LTFISH may be therefore a useful labelling technique whenever the chromosomal morphology had to be preserved after specific labelling of DNA regions. Binding mechanisms of single‐stranded DNA probes to double‐stranded DNA targets are discussed.     

Patterning DNA on microm scale on mica

Double-stranded DNA molecules were patterned by selective adsorption to aminosilane patterns on mica surfaces. Line patterns with 10 microm spacing were made by photolithography and transferred to a polymer stamp. The stamp was then used for applying aminosilane molecules by microcontact-printing technique on mica substrates. We applied DNA in Tris-EDTA (TE) buffer solution on the patterned substrate, and incubated it for 5 min at room temperature. The sample was then rinsed with pure water, and dried with nitrogen gas. Tapping mode force microscopy showed that DNA was adsorbed selectively on the aminosilanized parts of the mica substrate. We also tried to bridge two aluminum electrodes with DNA using AC electrophoresis.