Proton-fueled DNA-duplex-based stimuli-responsive reversible assembly of single-walled carbon nanotubes

Single-walled carbon nanotubes (SWNTs) have received much attention in nanotechnology because of their potential applications in molecular electronics, field-emission devices, biomedical engineering, and biosensors. Carbon nanotubes as gene and drug delivery vectors or as "building blocks" in nano-/microelectronic devices has been successfully explored. However, since SWNTs lack chemical recognition, SWNT-based electronic devices and sensors are strictly related to the development of a bottom-up self-assembly technique. Here we present an example of using DNA duplex-based protons (H(+)) as a fuel to control reversible assembly of SWNTs without generation of waste duplex products that poison DNA-based systems.     

Surface properties of fluorinated single-walled carbon nanotubes

Single-walled carbon nanotubes (SWCNTs) were fluorinated at several different temperatures. The change of atomic and electronic structures of fluorinated SWCNTs was investigated using X-ray photoelectron spectroscopy (XPS), electrical resistivity measurements and transmission electron microscopy (TEM). The amount of doped fluorine increases with increasing doping temperature, and the fluorine atoms are covalently attached to the side-wall of the SWCNTs. From Raman spectra and HRTEM study, the strong fluorination on the SWCNTs leads to the breaking of carbon–carbon bonds and the disintegration of tube structure. Several intermediate phases of fluorinated SWCNTs are observed during e-beam irradiation in HRTEM.     

Capillary electrophoresis of covalently functionalized single‐chirality carbon nanotubes

We demonstrate the separation of chirality‐enriched single‐walled carbon nanotubes (SWCNTs) by degree of surface functionalization using high‐performance CE. Controlled amounts of negatively charged and positively charged functional groups were attached to the sidewall of chirality‐enriched SWCNTs through covalent functionalization using 4‐carboxybenzenediazonium tetrafluoroborate or 4‐diazo‐N,N‐diethylaniline tetrafluoroborate, respectively. Surfactant‐ and pH‐dependent studies confirmed that under conditions that minimized ionic screening effects, separation of these functionalized SWCNTs was strongly dependent on the surface charge density introduced through covalent surface chemistry. For both heterogeneous mixtures and single‐chirality‐enriched samples, covalently functionalized SWCNTs showed substantially increased peak width in electropherogram spectra compared to nonfunctionalized SWCNTs, which can be attributed to a distribution of surface charges along the functionalized nanotubes. Successful separation of functionalized single‐chirality SWCNTs by functional density was confirmed with UV‐Vis‐NIR absorption and Raman scattering spectroscopies of fraction collected samples. These results suggest a high degree of structural heterogeneity in covalently functionalized SWCNTs, even for chirality‐enriched samples, and show the feasibility of applying CE for high‐performance separation of nanomaterials based on differences in surface functional density.     

The preparation of functionalized single walled carbon nanotubes as high efficiency DNA carriers

The positively charged single walled carbon nanotubes (SWNTs~ ) were prepared by conjugating with-CONH-C_6H_(12)-NH_3~ . The double strand DNA(dsDNA) chains were loaded onto SWNTs~ via the electrostatic interactions.SWNTs~ shows improved loading efficiency (353.5μg/mg) toward dsDNA compared with that of charged free single walled carbon nanotubes (SWNTs) (82.9μg/mg).     

Thermal decomposition and electron microscopy studies of single-walled carbon nanotubes

Thermoanalytical and electron microscopic methods were used as characterisation tools for the determination of the composition of single walled carbon nanotube samples. Acid purification method of single-walled carbon nanotubes (SWCN) proved to be effective, resulting in a three fold increase in the percentage of SWNTs present in the purified product as determined by thermogravimetric analysis. In this work we report the thermogravimetric analysis by conventional and high resolution methods of the raw SWNTs and purified SWNTs.     

Stability of narrow zigzag carbon nanotubes

First principles calculations of the electronic structure and total energy of narrow zigzag carbon nanotubes and their corresponding flat graphene strips have been carried out to assess the relative stability of the tube form. The results indicate that the smallest energetically stable carbon nanotube has a radius of about 0.2 nm. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

Preparation of single-walled carbon nanotube fiber coating for solid-phase microextraction of organochlorine pesticides in lake water and wastewater

The feasibility of single-walled carbon nanotubes (SWCNTs) as adsorbents for solid-phase microextraction was investigated by using organochlorine pesticides (OCPs) as model compounds. SWCNTs were attached onto a stainless steel wire through organic binder. Potential factors affecting the extraction efficiency were optimized, including extraction time, extraction temperature, desorption time, desorption temperature, and salinity. The developed method has a linear range of 2-800 ng/L for most analytes, with coefficients of correlation ranging from 0.9911 to 0.9996, LODs ranged from 0.19 to 3.77 ng/L (S/N = 3), and RSDs in the range of 3.5-13.9% (n = 5). Compared with the commercial PDMS fiber, the SWCNT fiber has better thermal stability (over 350 degrees C) and longer life span (over 150 times). The developed method was applied to determine trace OCPs in lake water and wastewater samples with external standard calibration. Results showed that OCP contamination was very low in these samples, and HCHs were detected in almost all water samples while DDT concentrations were almost under detection limits in these samples. Recoveries obtained at 20 ng/L spiking level were in the range of 88.4-111% for OCPs in lake water. For wastewater samples, however, the recoveries were satisfactory for HCHs (63.6-97.1%) but relatively low for DDTs (44.7-116%) due to the high content of organic matter in wastewater.     

Enhanced separation of Compound Xueshuantong capsule using functionalized carbon nanotubes with cationic surfactant solutions in MEEKC

A novel additive of multi‐walled carbon nanotubes (MWNTs) dispersed with cationic surfactants or mixed cationic/anionic surfactants was used for MEEKC separation of eight phenolic compounds, four glycosides, and one phenanthraquinone. In this context, several parameters affecting MEEKC separation were studied, including the dispersion agents of MWNTs, MWNTs content, oil type, SDS concentration, and the type and concentration of cosurfactant. Compared with conventional MEEKC, the addition of all types of MWNTs dispersions using single or mixed cationic surfactant solutions in running buffers was especially useful for improving the separation of solutes tested, as they influenced the partitioning between the oil droplets and aqueous phase due to the exceptional electrical properties and large surface areas of MWNTs. Use of cationic surfactant‐coated MWNTs (6.4 μg/mL) as the additive in a microemulsion buffer (0.5% octanol, 2.8% SDS, 5.8% isopropanol, and 5 mM borate buffer) yielded complete resolution of 13 analytes. The proposed method has been successfully applied for the detection and quantification of the studied compounds in a complex matrix sample (Compound Xueshuantong capsule).     

Fluorination of single walled carbon nanotubes at low temperature: Towards the reversible fluorine storage into carbon nanotubes

Fluorination of single walled carbon nanotubes was carried out at low temperature in the −191/25 °C range under 1 atm pure fluorine gas. In such conditions, the resulting C–F bonding is significantly weaker than for samples fluorinated at 280 °C. If the fluorination is performed at low temperature, fluorine atoms can be then removed from the host structure by moderated heating until 300 °C or by vacuum without strong damage on the tubes. After thermal defluorination, the resulting sample can be refluorinated similarly than the pristine tubes.     

Evaluation of the solid-phase microextraction fiber coated with single walled carbon nanotubes for the determination of benzene,toluene, ethylbenzene,xylenes in aqueous samples

A solid-phase microextraction (SPME) fiber coated with single walled carbon nanotubes (SWCNTs) was prepared by electrophoretic deposition and treated at 500 °C in H₂ stream. In order to evaluate the characteristics of the obtained fiber, it was applied in the headspace solid-phase microextraction (HS-SPME) of benzene, toluene, ethylbenzene and xylenes (BTEX) from water sample and quantification by gas chromatography with flame ionization detection (GC-FID). The results indicated that the thermal treatment with H₂ enhanced the extraction of the SWCNTs fiber for BTEX significantly. Thermal stability and durability of the fiber were also investigated, showing excellent stability up to 350 °C and life time over 120 times. In the comparison with the commercial CAR–PDMS fiber, the SWCNTs fiber showed similar and higher extraction efficiencies for BTEX. Under the optimized conditions, the linearity, LODs (S/N = 3) and LOQs (S/N = 10) of the method based on the SWCNTs fiber were 0.5–50.0, 0.005–0.026 and 0.017–0.088 μg/L, respectively. Repeatability for one fiber (n = 3) was in the range of 1.5–5.6% and fiber-to-fiber reproducibility (n = 3) was in the range of 4.2–8.3%. The proposed method was successfully applied in the analysis of BTEX compounds in seawater, tap water and wastewater from a paint plant.     

Dielectrophoretic manipulation of nanomaterials: A review

Nanomaterials manipulation using dielectrophoresis (DEP) is one of the major research areas that could potentially benefit the micro/nano science for diverse applications, such as microfluidics, nanomachine, and biosensor. The innovation and development of basic theories, methods or applications will have a huge impact on the entire related field. Specifically, for DEP manipulation of nanomaterials, improvements in comprehensive performance of accuracy, flexibility and scale could promote broader applications in micro/nano science. Therefore, to explore the directions for future research, this paper critically provides an overview on the fundamentals, recent progress, current challenges, and potential applications of DEP manipulation of nanomaterials. This review will also act as a guide and reference for researchers to explore promising applications in relevant research.     

Carbon nanotube-nucleobase hybrids: nanorings from uracil-modified single-walled carbon nanotubes

Single‐walled carbon nanotubes (SWCNTs) have been covalently functionalized with uracil nucleobase. The hybrids have been characterized by using complementary spectroscopic and microscopic techniques including solid‐state NMR spectroscopy. The uracil‐functionalized SWCNTs are able to self‐assemble into regular nanorings with a diameter of 50–70 nm, as observed by AFM and TEM. AFM shows that the rings do not have a consistent height and thickness, which indicates that they may be formed by separate bundles of CNTs. The simplest model for the nanoring formation likely involves two bundles of CNTs interacting with each other via uracil–uracil base‐pairing at both CNT ends. These nanorings can be envisaged for the development of advanced electronic circuits.     

Coherent electronic transport through the single-walled carbon nanotubes

We present the results for coherent electronic transport through the single walled carbon nanotubes. A large value of conductance is obtained for strong coupling to the electrodes, which is close to the ideal transmission of 4e²/h as in experiment. We also consider the system with ferromagnetic electrodes and analyze in detail conductance for separated channels in the coherent regime.     

Probing charge transfer between shells of double-walled carbon nanotubes sorted by outer-wall electronic type

Double-walled carbon nanotubes (DWCNTs) with outer metallic (M) or semiconducting (S) shells were sorted by density-gradient ultracentrifugation and examined by Raman spectroscopy and in situ Raman spectroelectrochemistry. The combination of sorting and the selection of appropriate laser excitation energies allowed the disentanglement of the effects of different variations of the electronic type (M or S) of the inner and outer tubes in DWCNTs on the doping behavior and charge transfer between the inner and outer walls. Charge transfer from the outer tube to the inner tube occurs only if the electronic states of the outer tube are filled with electrons or holes, and if these filled states are higher in energy than those of the inner tube. Therefore, each combination of inner and outer tube (i.e., inner@outer: M@M, M@S, S@M, and S@S) exhibits a distinct behavior. The potential needed to observe the effects of charge transfer between the inner and outer tubes is found to increase in the following order: M@M < S@M < M@S < S@S.     

Rheology of polycarbonate reinforcedwith functionalized and unfunctionalized single-walled carbon nanotubes

Nanocomposites of polycarbonate (PC) containing low concentrations of pristine and COOH and OH functionalized single-walled carbon nanotubes (SWNTs, COOH-SWNTs and OH-SWNTs) were prepared by melt-mixing and analyzed using rheology and scanning electron microscopy (SEM). The steady state and linear viscoelastic behavior of each nanocomposite material is presented and compared to that of the neat PC. SEM analysis revealed that samples containing functionalized SWNTs were more dispersible than samples containing the pristine SWNTs.     

Pegylated single-walled carbon nanotubes with gelable block copolymers

Functional amphiphilic block copolymer poly（ethylene glycol）-block-poly[（3-（triethoxysilyl）propyl methacrylate）-co -（1-pyrene-methyl） methacrylate],PEG₁₁₃-b-P(TEPM₂₆-co-PyMMA₄),was synthesized via atom transfer radical polymerization（ATRP） initiated by monomethoxy capped poly（ethylene glycol） bromoisobutyratc.This polymer exhibited strong ability to disperse and exfoliate single-walled carbon nanotubes（SWNTs） in different solvents due to the adhesion of pyrene units to surface of SWNTs.In aqueous solution,the PTEPM segments that were located on the nanotube surfaces with the pyrene units could be gelated and,as a result,the silica oxide networks with PEG coronas were formed on the surface of nanotubes,which ensured the composites with a good dispersibility and stability.Furthermore,functional silane coupling agents,3-mercaptopropyltrimethoxysilane and 3-aminopropyltriethoxysilanc,were introduced during dispersion of SWNTs using the block copolymers.They were co-gelated with PTEPM segments,and the-SH and-NH₂ functionalities were introduced into the silica oxide coats respectively.     

Covalent sidewall functionalization of single-walled carbon nanotubes by amino acids

Single-walled carbon nanotubes (SWNTs) with amino acids covalently attached to their side walls, viz., “nanotube-aminoacids,” have been prepared starting from colloidal solutions of fluorinated SWNTs (F-SWNTs) and amino acids in o-dichlorobenzene and heating at 80–150 °C in the presence of pyridine. The syntheses were carried out with the F-SWNTs of approximately 2: 1 (C: F) stoichiometry and several natural α-aino acids with both pro-tected and unprotected carboxyl groups, such as glycine ethyl ester hydrochloride, L-serine ethyl ester hydrochloride, l-cysteine, and trans-4-hydroxy-l-proline. The nanotube-aminoacids have been characterized by Raman and FTIR spectroscopy, atomic force, scanning, and transmission electron microscopies, and thermal gravimetric analysis (TGA). Based on TGA data, the degree of sidewall functionalization in the synthesized SWNT derivatives was estimated to be in the range from one of 32 to one of 8 carbon atoms, depending on the amino acid nature and reaction conditions used. The amino acid-functionalized SWNTs, prepared in this work by simple and inexpensive one-step method, can be valuable precursors for peptide synthesis and targeted drug delivery, design and fabrication of nanocomposites and fibers, and other biomedical and engineering applications. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1035–1043, May, 2008.     

Multi‐walled carbon nanotubes encapsulated with polyurethane and its nanocomposites

Poly(acryloyl chloride) (PACl) was employed to enhance the surface of multi‐walled carbon nanotubes (MWCNTs). MWCNTs were first acid treated to generate hydroxyl groups on the surface, which was reacted with PACl to obtain an encapsulation. The numerous acryloyl chloride groups on the out layer were esterified with a proper amount of ethylene glycol (EG). Subsequently, 4,4′‐methylenebis (phenylisocyanate) (MDI) and 1,4‐butanediol (BDO) were introduced into the system, and a polyurethane (PU) layer was formed in situ. The formation of PU layers on MWCNTs was confirmed by Fourier transform infrared spectrometer (FTIR) and X‐ray photoelectron spectroscope (XPS). The morphology of encapsulated MWCNTs was observed by transmission electron microscope (TEM) and scanning electron microscope (SEM). Thermo gravimetric analysis (TGA) showed the grafted polymer fraction was up to 90%. On introducing the modified MWCNTs into a PU matrix, an increase in tensile strength by 60.6% and improvement in modulus by 6.3% over neat PU was observed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4857–4865, 2008