Suspended Single-walled Carbon Nanotubes Research Articles

Effect of Surfactant Type and Redox Polymer Type on Single-Walled Carbon Nanotube Modified Electrodes

Electrodes modified with single-walled carbon nanotubes (SWNTs) offer a number of attractive properties for developing novel electrochemical sensors. A common method to immobilize SWNTs onto the electrode surface is by placing a droplet of a SWNT suspension onto the electrode surface and allowing the solvent to evaporate. In order to maximize the properties of individual SWNTs, surfactants are normally present in these suspensions to provide stable and homogeneous SWNT dispersions. In this study we investigated the effect of different surfactants on the electrochemical and enzymatic performance of SWNT modified glassy carbon electrodes (GCEs). Amperometic biosensors for glucose were fabricated by a two-step procedure. In the first step, SWNT films were deposited onto GCEs by solution casting suspensions of SWNTs in water, Triton X-100, Tween 20, sodium cholate or sodium dodecylbenzenesulfonate (NaDDBS). In the second step, hydrogels containing a redox polymer and the enzyme, glucose oxidase (GOX), were deposited and cross-linked onto the SWNT-modified GCE. Three different redox polymers were tested: 3-ferrocenylpropyl-modified LPEI, (Fc-C3-LPEI), 6-ferrocenylhexyl-modified LPEI, (Fc-C6-LPEI), and poly[(vinylpyridine)Os(bipyridyl)2Cl](2+/3+)(PVP-Os). Biosensors constructed with SWNT films from suspensions of Triton X-100 or Tween 20 generally produced the highest electrochemical and enzymatic responses, with Triton X-100 films producing current densities of ~1.7-2.1 mA/cm(2) for the three different redox polymers. In contrast, biosensors constructed with SWNT films from sodium cholate suspensions resulted in significant decreases in the electrochemical and enzymatic response and in some cases showed no enzymatic activity. The results with SWNT films from NaDDBS suspensions were dependent upon the specific redox polymer used, but in general gave reduced enzymatic responses (~0.05-0.4 mA/cm(2)). These results demonstrate the importance of surfactant type in fabricating SWNT-modified electrode films.

Evaporative Self-Assembly of Single-Walled Carbon Nanotubes for Field Effect Transistor

Controlling the stick and slip motions of the contact lines in a confined geometry comprised of a spherical lens with a flat substrate is useful for manufacturing polymer ring patterns. We used a sphere on a flat geometry, by which we could control the interfaces of the solution, vapor and substrate. By this method, hundreds of concentric ring-pattern formations of a linear conjugated polymer, poly [2-methoxy-5-(2-thylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), were generated with excellent regularity over large areas after complete solvent evaporation. Subsequently, the MEH-PPV ring patterns played a role as a directed template to organize highly regular concentric rings of single-walled carbon nanotubes(SWCNTs); when a droplet of the SWCNT suspension in water was casted onto the prepared substrate, hydrophobic polymer patterns confined the water dispersed SWCNTs in between the hydrophilicized <TEX>$SiO_2/Si$</TEX> substrate. As the solvent evaporated, SWCNT-rings were formed in between MEH-PPV rings with controlled density. Finally, we used a lift-off process to produce SWCNT patterns by the removal of a sacrificial polymer template with organic solvent. We also fabricated a field effect transistor using self-assembled SWCNT networks on a <TEX>$SiO_2/Si$</TEX> substrate.

First-passage theory of exciton population loss in single-walled carbon nanotubes reveals micron-scale intrinsic diffusion lengths

One-dimensional crystals have long range translational invariance which manifests as long exciton diffusion lengths, but such intrinsic properties are often obscured by environmental perturbations. We use a first-passage approach to model single-walled carbon nanotube (SWCNT) exciton dynamics (including exciton-exciton annihilation and end effects) and compare it to results from both continuous-wave and multipulse ultrafast excitation experiments to extract intrinsic SWCNT properties. Excitons in suspended SWCNTs experience macroscopic diffusion lengths, on the order of the SWCNT length (1.3--4.7 $\ensuremath{\mu}$m), in sharp contrast to encapsulated samples. For these pristine samples, our model reveals intrinsic lifetimes (350--750 ps), diffusion constants (130--350 cm${}^{2}$/s), and absorption cross sections (2.1--$3.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}$ cm${}^{2}$/atom) among the highest previously reported.

Single-walled carbon nanotube buckypapers as electrocatalyst supports for methanol oxidation

This work studies the use of various single-walled carbon nanotube (SWCNT) buckypapers as catalyst supports for methanol electro-oxidation in acid media. Buckypapers were obtained by vacuum filtration from pristine and oxidized SWCNT suspensions in different liquid media. Pt–Ru catalysts supported on the buckypapers were prepared by multiple potentiostatic pulses using a diluted solution of Pt and Ru salts (2 mM H2PtCl6 + 2 mM RuCl3) in acid media. The resulting materials were characterized via SEM, TEM, EDX and ICP-OES analysis. Well dispersed rounded nanoparticles between 2 and 15 nm were successfully electrodeposited on the SWCNT buckypapers. The ruthenium content in the bimetallic deposits was between 32 and 48 at. %, while the specific surface areas of the catalysts were in the range of 72–113 m2 g−1. It was found that the solvent used to prepare the SWCNT buckypaper films has a strong influence on the catalyst dispersion, particle size and metal loading. Cyclic voltammetry and chronoamperometry experiments point out that the most active electrodes for methanol electro-oxidation were prepared with the buckypaper supports that were obtained from SWCNT dispersions in N-methyl-pyrrolidone.

Risks of Single-Walled Carbon Nanotubes Acting as Contaminants-Carriers: Potential Release of Phenanthrene in Japanese Medaka (Oryzias latipes)

The performance of carbon nanotubes (CNTs) acting as contaminants-carriers in vivo is critical for understanding the environmental risks of CNTs. In this study, the whole-body accumulation and tissue distribution of phenanthrene in Japanese medaka was examined in the presence of single-walled carbon nanotubes (SWCNTs) and the potential release of phenanthrene was investigated from two types of SWCNTs suspensions that differed in surface charge and stability. The results showed that the coexistence of SWCNTs facilitated the accumulation of phenanthrene in the digestive track of fish and therefore enhanced the whole-body phenanthrene concentration by 2.1 fold after exposure for 72 h. Meanwhile, 6.4-48 and 20-34 times higher phenanthrene concentrations were measured in the liver and brain of fish exposure to the two mixtures, respectively, when comparing with the phenanthrene alone treatment with equal concentration of soluble phenanthrene. The extra phenanthrene was from the SWCNTs-associated phenanthrene that accumulated in the digestive track indicating the release of phenanthrene from SWCNTs did occur in fish. Moreover, the neutrally charged SWCNTs showed different agglomeration behaviors from the negatively charged SWCNTs, which could affect the accumulation of SWCNTs in the digestive track of fish and subsequently influence the retention of phenanthrene associated with the carbon nanotubes.

Separation of Single-Walled Carbon Nanotubes by 1-Dodecanol-Mediated Size-Exclusion Chromatography

A simple, single-column, high-throughput fractionation procedure based on size-exclusion chromatography of aqueous sodium dodecyl sulfate suspensions of single-walled carbon nanotubes (SWCNTs) is presented. This procedure is found to yield monochiral or near monochiral SWCNT fractions of semiconducting SWCNTs. Unsorted and resulting monochiral suspensions are characterized using optical absorption and photoluminescence spectroscopy.

Gene expression and biochemical responses in brain of zebrafish Danio rerio exposed to organic nanomaterials: Carbon nanotubes (SWCNT) and fullerenol (C60(OH)18–22(OK4))

Nanomaterials (NM) industry had grown in the last decade, although there are few studies concerning its potential toxicity effects on aquatic organisms. In this study the freshwater zebrafish (Danio rerio) was exposed to two kinds of carbon NM, single-wall carbon nanotubes (SWCNT) and fullerenol [C60(OH)18–22(OK4)] to analyze oxidative stress responses on fish brain. Adult zebrafish (mean mass: 0.52±0.01g) were submitted to intraperitoneal injections of SWCNT suspension and fullerenol solution (30mg/kg of fish), receiving one or two doses with a time interval of 24h. Results showed that total antioxidant capacity was lowered in brains of fish exposed 24h to fullerenol when compared to those from SWCNT treatment (p<0.05). After 48h, fullerenol induced higher expression of both catalytic and regulatory subunits of enzyme glutamate cysteine ligase when compared to control group (p<0.05), indicating an antioxidant behavior. In vitro assays showed a dual effect of SWCNT, since a pro-oxidant behavior was observed at low concentrations (0.1 and 1.0mg/L) and an antioxidant one at the highest concentration (10.0mg/L). Few biological responses were altered by this NM: decrease in total antioxidant capacity and induction of the expression of the transcription factor Nrf2 when compared to control group.

Chirality‐Dependent Reactivity of Individual Single‐Walled Carbon Nanotubes

Electronic characteristics of a single-walled carbon nanotube (SWCNT) strongly depend on minor variations in its atomic arrangement, specifically chirality. Therefore, precise control over nanotube chirality is highly desired for their application. Theoretically, SWCNTs with different structures have different chemical reactivities, which can be further used for their chirality selection. Here, an approach is developed to examine the relationship between the chirality of SWCNTs and their intrinsic chemical reactivity. By oxidizing individual, high-quality, suspended SWCNTs and using the nanobeam electron diffraction technique, it is shown that the reactivity of SWCNTs to O2 is intricately related to their diameters, metallicity, and chiral angles. In particular, even minor differences in chiral angles lead to big differences in their reactivity, which concords with first-principles calculations. Based on the experimental observations, a chirality-dependent reactivity sequence is constructed for SWCNTs. These findings shed light on effective chiral separation of SWCNTs for their practical application in many fields.

Self-assembly of carbon nanotube films from room temperature ionic liquids

A novel method for the assembly of thin, uniform transparent and conductive films of single-walled carbon nanotubes (SWCNTs) on glass substrates is described. This process involves the initial transfer of a temporary suspension of SWCNTs in room temperature ionic liquid to the surface of water and the subsequent transfer of the SWCNT film onto a glass substrate. The average sheet resistance of the films was determined by four point probe measurements to be 1.52 and 4.13kΩ/sq, with an average optical transparency of 50% and 63%, respectively.

Single cell in-vivo carbon nanotube device with multimodal sensing potential

Single walled carbon nanotube (SWNT) field effect transistors (NTFETs) are quickly becoming the foundation for bioelectronic sensors. We describe a multimodal NTFET device that could be used as a real time single cell biosensor with the potential for chemical, optical and electrical sensing capabilities. This device utilizes the natural movement of a cell through the trench of a NTFET to provide a working cell-SWNT interaction where the nanotube is suspended. The use of individual suspended SWNTs in lieu of non-suspended SWNTs in our device provides the basis for an in vivo NTFET multimodal single cell biosensor.

Mechanism of Electrolyte-Induced Brightening in Single-Wall Carbon Nanotubes

While addition of electrolyte to sodium dodecyl sulfate suspensions of single-wall carbon nanotubes has been demonstrated to result in significant brightening of the nanotube photoluminescence (PL), the brightening mechanism has remained unresolved. Here, we probe this mechanism using time-resolved PL decay measurements. We find that PL decay times increase by a factor of 2 on addition of CsCl as the electrolyte. Such an increase directly parallels an observed near-doubling of PL intensity, indicating the brightening results primarily from changes in nonradiative decay rates associated with exciton diffusion to quenching sites. Our findings indicate that a reduced number of these sites results from electrolyte-induced reorientation of the surfactant surface structure that partially removes pockets of water from the tube surface where excitons can dissociate, and thus underscores the contribution of interfacial water in exciton recombination processes.

The characterization of the concentration of the single-walled carbon nanotubes in aqueous dispersion by UV-Vis-NIR absorption spectroscopy

Current and future applications of single-wall carbon nanotubes (SWCNTs) depend on the dispersion of the SWCNTs in aqueous solution and their quantitation. The concentration of SWCNTs is an important indicator to evaluate the dispersibility of the surfactant-dispersed SWCNTs suspension. Due to the complexity of the SWCNTs suspension, it is necessary to determine both the total concentration of the dispersed SWCNTs and the concentration of individually dispersed SWCNTs in aqueous suspensions, and these were evaluated through the absorbance and the resonance ratios of UV-Vis-NIR absorption spectra, respectively. However, there is no specific and reliable position assigned for either calculation of the absorbance or the resonance ratio of the UV-Vis-NIR absorption spectrum. In this paper, different ranges of wavelengths for these two parameters were studied. From this, we concluded that the wavelength range between 300 nm and 600 nm should be the most suitable for evaluation of the total concentration of dispersed SWCNTs in the suspension; also, wavelengths below 800 nm should be most suitable for evaluation of the concentration of individually dispersed SWCNTs in the suspension. Moreover, these wavelength ranges are verified by accurate dilution experiments.

When dithiafulvenyl functionalized π-conjugated oligomers meet fullerenes and single-walled carbon nanotubes

A series of π-conjugated oligomers taking linear and Z-shaped molecular structures were synthesized with electron-donating dithiafulvenyl (DTF) groups functionalized at the terminal positions. Besides significantly enriched electronic and redox properties as disclosed by UV-Vis absorption and voltammetric analyses, these DTF-endcapped oligomers also exhibited a facile reactivity of oxidative CC bond cleavage sensitized by fullerenes under air, converting the non-fluorescent DTF–oligomers to highly fluorescent aldehyde-endcapped oligomer products. This reaction provides an appealing approach for efficient fluorescence turn-on sensing of fullerenes. Furthermore, the DTF-attached oligomers showed strong noncovalent interactions with single-walled carbon nanotubes (SWNTs) to form soluble supramolecular assemblies in certain chlorinated organic solvents such as methylene chloride and chloroform. The dispersion of SWNTs effected by the DTF–oligomers was found to be highly efficient (up to 0.29 mg of SWNTs per mL) and shows selectivity for small-diameter nanotubes. The resulting SWNT suspensions could be easily dissociated upon addition of hydrocarbon solvents such as hexanes, releasing pristine SWNTs which were free of oligomer dispersants after filtration and solvent rinsing.

Highly efficient exfoliation of individual single-walled carbon nanotubes by biocompatible phenoxylated dextran

Highly efficient exfoliation of individual single-walled carbon nanotubes (SWNTs) was successfully demonstrated by utilizing biocompatible phenoxylated dextran, a kind of polysaccharide, as a SWNT dispersion agent. Phenoxylated dextran shows greater ability in producing individual SWNTs from raw materials than any other dispersing agent, including anionic surfactants and another polysaccharide. Furthermore, with this novel polymer, SWNT bundles or impurities present in raw materials are removed under much milder processing conditions compared to those of ultra-centrifugation procedures. There exists an optimal composition of phenoxy groups (∼13.6 wt%) that leads to the production of high-quality SWNT suspensions, as confirmed by UV-vis-nIR absorption and nIR fluorescence spectroscopy. Furthermore, phenoxylated dextran strongly adsorbs onto SWNTs, enabling SWNT fluorescence even in solid-state films in which metallic SWNTs co-exist. By bypassing ultra-centrifugation, this low-energy dispersion scheme can potentially be scaled up to industrial production levels.

New hybrid materials with porphyrin-ferrocene and porphyrin-pyrene covalently linked to single-walled carbon nanotubes

Novel porphyrin derivatives bearing additional pyrene or ferrocene units as light harvesting antenna systems were synthesized and fully characterized. Following a covalent functionalization approach for single-walled carbon nanotubes (SWCNTs), stable SWCNT suspensions in common organic solvents were produced. Subsequently, the resulting porphyrin-pyrene and porphyrin-ferrocene dyads were incorporated onto the nanotubes' backbone yielding donor–donor–acceptor hybrids. The resulting hybrid materials were soluble in common organic solvents and were characterized using micro-Raman, ATR-IR, UV-Vis and photoluminescence spectroscopy, transmission electron microscopy, thermogravimetric analysis and electrochemistry. Photoluminescence quenching of the porphyrin emission in both hybrid materials was detected thus suggesting the potentiality of these materials in photoelectrochemical cells.

Photoluminescence microscopy and spectroscopy of individualized and aggregated single-wall carbon nanotubes

We have studied photophysical properties of individual single-wall carbon nanotubes (SWNTs) and SWNT aggregates in colloidal suspensions using fluorescence microscopy, -spectroscopy and time-correlated single photon counting. The results suggest that SWNT aggregates, formed by addition of a divalent salt to a monomer SWNT suspension, have an open structure with a density of ≈12SWNTsμm−3. We also find a sizable spectral red-shift of 16nm, line-broadening of 23nm and reduced PL lifetimes in coagulated structures, independent of aggregate size for the range of structures studied here. Such changes may be used as fingerprint of SWNT aggregate formation in similar environments.

Dye-assisted dispersion of single-walled carbon nanotubes for solution fabrication of NO2 sensors

Direct golden orange dye molecules were used as a dispersing agent to produce suspensions of single-walled carbon nanotubes (SWCNTs) in water. Uniform, thin film networks were fabricated by vacuum filtration using different concentrations of SWCNT and transferred subsequently to glass substrates. The dispersion efficiency was compared to other surfactants. Measurement of the sheet resistance as a function of SWCNT concentration showed a transition from 2D percolation to 3D conduction behaviour when the concentration of SWCNTs exceeded 0.001 mg/mL. The electrical response to NO2 gas exposure was investigated as a function of temperature and an optimum response was observed at 200°C.

Development of a Novel Composite Material with Carbon Nanotubes Assisted by Self-Assembled Peptides Designed in Conjunction with β-Sheet Formation

A novel composite material is developed with single-walled carbon nanotubes (SWCNTs) and artificially designed peptides, and its chemical and physicochemical characteristics are evaluated with an aim toward biomedical application. The peptides were designed to form a β-sheet structure that would be suitable for wrapping SWCNTs. The complex of SWCNTs and peptide (SWCNT-peptide) showed good dispersibility in aqueous media and was considerably stable even in the absence of an excess amount of peptide in the media. The formation of SWCNT-peptide was confirmed by its performance in water, atomic force microscopy and transmission electron microscopy observation, and molecular modeling. The possibility of introducing various functions to SWCNT-peptide was also demonstrated by several methods, such as introduction of special amino acids, chemical modification, and additional complex formation based on electrostatic interaction. These results suggest the potential of the SWCNT-peptide complex as a molecular platform on which a desirable structure and/or function can be constructed for biomedical and industrial application.

Few-Hundred GHz Carbon Nanotube Nanoelectromechanical Systems (NEMS)

We study 23-30 nm long suspended single-wall carbon nanotube quantum dots and observe both their stretching and bending vibrational modes. We use low-temperature DC electron transport to excite and measure the tubes' bending mode by making use of a positive feedback mechanism between their vibrations and the tunneling electrons. In these nanoelectromechanical systems (NEMS), we measure fundamental bending frequencies f(bend) ≈ 75-280 GHz and extract quality factors Q ∼ 10(6). The NEMS's frequencies can be tuned by a factor of 2 with tension induced by mechanical breakjunctions actuated by an electrostatic force or tension from bent suspended electrodes.

Dielectrophoretic assembly of suspended single-walled carbon nanotubes

Graphical abstractDisplay Omitted Highlights? Dielectrophoresis process conditions optimized for individual SWCNT devices yield. ? Electric field frequency and SWCNT dispersion concentration are critical parameters. ? Critical point drying successfully used to avoid stiction of assembled SWCNTs. We report a detailed study of dielectrophoretic assembly of single-walled carbon nanotube (SWCNT) devices intended for nano electromechanical systems (NEMS) applications. The process conditions of dielectrophoresis (DEP) are optimized to maximize the yield of devices with only one SWCNT bridging the electrode structures. The frequency of the applied electric field and the concentration of the SWCNT dispersion were found to be important parameters for assembling single SWCNT per device site. Critical point drying (CPD) has been successfully used to avoid stiction of the assembled SWCNTs during the final drying and release step. Electrical measurements performed with the as-assembled nanotubes reveal the presence of both metallic and semiconducting SWCNTs.