Single-walled Carbon Nanotubes In Water Research Articles

Aqueous dispersion of single walled carbon nanotubes stabilized by PEG modified diperylene bisimide and their application as an antibacterial agent

Polyethylene glycol modified diperylene bisimide was synthesized and applied to disperse single-walled carbon nanotubes in water. Moreover, the well-dispersed SWCNTs show excellent antibacterial activities.

Delivering Single-Walled Carbon Nanotubes to the Nucleus Using Engineered Nuclear Protein Domains.

Single-walled carbon nanotubes (SWCNTs) have great potential for cell-based therapies due to their unique intrinsic optical and physical characteristics. Consequently, broad classes of dispersants have been identified that individually suspend SWCNTs in water and cell media in addition to reducing nanotube toxicity to cells. Unambiguous control and verification of the localization and distribution of SWCNTs within cells, particularly to the nucleus, is needed to advance subcellular technologies utilizing nanotubes. Here we report delivery of SWCNTs to the nucleus by noncovalently attaching the tail domain of the nuclear protein lamin B1 (LB1), which we engineer from the full-length LMNB1 cDNA. More than half of this low molecular weight globular protein is intrinsically disordered but has an immunoglobulin-fold composed of a central hydrophobic core, which is highly suitable for associating with SWCNTs, stably suspending SWCNTs in water and cell media. In addition, LB1 has an exposed nuclear localization sequence to promote active nuclear import of SWCNTs. These SWCNTs-LB1 dispersions in water and cell media display near-infrared (NIR) absorption spectra with sharp van Hove peaks and an NIR fluorescence spectra, suggesting that LB1 individually disperses nanotubes. The dispersing capability of SWCNTs by LB1 is similar to that by albumin proteins. The SWCNTs-LB1 dispersions with concentrations ≥150 μg/mL (≥30 μg/mL) in water (cell media) remain stable for ≥75 days (≥3 days) at 4 °C (37 °C). Further, molecular dynamics modeling of association of LB1 with SWCNTs reveal that the exposure of the nuclear localization sequence is independent of LB1 binding conformation. Measurements from confocal Raman spectroscopy and microscopy, NIR fluorescence imaging of SWCNTs, and fluorescence lifetime imaging microscopy show that millions of these SWCNTs-LB1 complexes enter HeLa cells, localize to the nucleus of cells, and interact with DNA. We postulate that the modification of native cellular proteins as noncovalent dispersing agents to provide specific transport will open new possibilities to utilize both SWCNT and protein properties for multifunctional subcellular targeting applications. Specifically, nuclear targeting could allow delivery of anticancer therapies, genetic treatments, or DNA to the nucleus.

Linear solvation energy relationship for the adsorption of synthetic organic compounds on single-walled carbon nanotubes in water

The linear solvation energy relationship (LSER) was applied to predict the adsorption coefficient (K) of synthetic organic compounds (SOCs) on single-walled carbon nanotubes (SWCNTs). A total of 40 log K values were used to develop and validate the LSER model. The adsorption data for 34 SOCs were collected from 13 published articles and the other six were obtained in our experiment. The optimal model composed of four descriptors was developed by a stepwise multiple linear regression (MLR) method. The adjusted r2 (r2adj) and root mean square error (RMSE) were 0.84 and 0.49, respectively, indicating good fitness. The leave-one-out cross-validation Q2 () was 0.79, suggesting the robustness of the model was satisfactory. The external Q2 () and RMSE (RMSEext) were 0.72 and 0.50, respectively, showing the model’s strong predictive ability. Hydrogen bond donating interaction (bB) and cavity formation and dispersion interactions (vV) stood out as the two most influential factors controlling the adsorption of SOCs onto SWCNTs. The equilibrium concentration would affect the fitness and predictive ability of the model, while the coefficients varied slightly.

The dispersion, solubilization and stabilization in “solution” of single-walled carbon nanotubes

Methods for the solubilization and dispersion of single-walled carbon nanotubes in water and organic solvents by physical and chemical methods have been reviewed.

Carbon nanotubes dispersed in aqueous solution by ruthenium(ii) polypyridyl complexes.

Cationic ruthenium(ii) polypyridyl complexes with appended pyrene groups have been synthesized and used to disperse single-walled carbon nanotubes (SWCNT) in aqueous solutions. To this end, planar pyrene groups enable association by means of π-stacking onto carbon nanotubes and, in turn, the attachment of the cationic ruthenium complexes. Importantly, the ionic nature of the ruthenium complexes allows the formation of stable dispersions featuring individualized SWCNTs in water as confirmed in a number of spectroscopic and microscopic assays. In addition, steady-state photoluminescence spectroscopy was used to probe the excited state interactions between the ruthenium complexes and SWCNTs. These studies show that the photoluminescence of both, that is, of the ruthenium complexes and of SWCNTs, are quenched when they interact with each other. Pump-probe transient absorption experiments were performed to shed light onto the nature of the photoluminescence quenching, showing carbon nanotube-based bands with picosecond lifetimes, but no new bands which could be unambigously assigned to photoinduced charge transfer process. Thus, from the spectroscopic data, we conclude that quenching of the photoluminescence of the ruthenium complexes is due to energy transfer to proximal SWCNTs.

Simulating adsorption of organic pollutants on N-doped single-walled carbon nanotubes in water

N-doped carbon nanotubes (N-CNTs) are widely used in various fields due to their excellent characters. They will be inevitably released into the environment with their extensive use. The adsorption of organic compounds on N-CNTs may affect the environmental behavior and ecological risk of both N-CNTs and pollutants. However, only few studies have been performed on the adsorption of organic compounds on N-CNTs in water. In this study, we constructed 20 N-doped single-walled carbon nanotubes (N-SWNTs) with different doping configurations and doping concentrations and simulated the adsorption of aromatic pollutants on N-SWNTs by density functional theory (DFT) calculations. Our simulation results indicated that N doping can increase the adsorption affinity of aromatic compounds on SWNTs, and doping configurations and doping concentrations show significant effect. Pyrid-N doped SWNTs with vacancy defect have a good performance on adsorption. The adsorption of aromatic compounds on N-SWNTs in water is physisorption. Hydrophobic interaction and p-p stacking are the main interaction forces. Functional groups of benzene derivatives (-NO 2 , -OH, -NH 2 ), can enhance electrostatic interactions between the aromatics and N-SWNTs. Our study will provide a theoretical guide for future ecological risk assessment of N-SWNTs.

Reactive oxygen species generation and dispersant-dependent electron transfer through single-walled carbon nanotubes in water

Although induction of oxidative stress is widely accepted as one of the major cytotoxic effects of carbon nanotubes (CNTs), there is no solid understanding of how biological redox reactions are affected and how reactive oxygen species (ROS) are generated by CNTs, especially when they are coated with various dispersing agents. In this study, we investigated electron transfer from biological reducing agents through nonfunctionalized single-walled carbon nanotubes (SWCNTs) to molecular oxygen, generating ROS in the process. Electron transfer rates in the colloidal SWCNT suspensions depended on the dispersant used to stabilize them, with six dispersants examined. Oxidation of both nicotinamide adenine dinucleotide (NADH) and dithiothreitol was catalyzed by SWCNTs coated with either cetyltrimethylammonium bromide (CTAB) or Suwannee River natural organic matter (SRNOM). SWCNTs coated with other types of surfactants showed only slight effect. In the presence of NADH or dithiothreitol, generation of ROS also was dispersant-dependent, with CTAB- and SRNOM-coated SWCNTs generating significant amounts of superoxide anion and hydrogen peroxide. In systems containing xanthine and xanthine oxidase, accumulated charge on the SWCNTs appeared to be transferred to superoxide anion, resulting in indirect disproportionation of superoxide anion, forming more hydrogen peroxide.

Solubilization of single-walled carbon nanotubes using a peptide aptamer in water below the critical micelle concentration.

The solubilizing ability of single-walled carbon nanotubes (SWCNTs) in water with several dispersants was investigated. Among the dispersants, including low-molecular-weight surfactants, peptides, DNA, and a water-soluble polymer, the peptide aptamer, A2 (IFRLSWGTYFS), exhibited the highest dispersion capability below the critical micelle concentration at a concentration of 0.02 w/v%. The dispersion of supernatant aqueous solution of SWCNTs containing aptamer A2 was essentially unchanged for several months after high-speed ultracentrifugation and gave rise to an efficient and stable dispersion of the SWCNTs in water. From the results of isothermal titration calorimetry and molecular dynamics simulations, the effective binding capability of A2 was due to π-π interaction between aromatic groups in the peptide aptamer and the side walls of SWCNTs. Interestingly, the peptide aptamer showed the possibility of diameter separation of semiconducting SWCNTs using a uniform density gradient ultracentrifuge. These phenomena are encouraging results toward an effective approach to the dispersion and separation of SWCNTs.

Simulating Molecular Interactions of Carbon Nanoparticles with a Double-Stranded DNA Fragment

Molecular interactions between carbon nanoparticles (CNPs) and a double-stranded deoxyribonucleic acid (dsDNA) fragment were investigated using molecular dynamics (MD) simulations. Six types of CNPs including fullerenes (C60and C70), (8,0) single-walled carbon nanotube (SWNT), (8,0) double-walled carbon nanotube (DWNT), graphene quantum dot (GQD), and graphene oxide quantum dot (GOQD) were studied. Analysis of the best geometry indicates that the dsDNA fragment can bind to CNPs through pi-stacking and T-shape. Moreover, C60, DWNT, and GOQD bind to the dsDNA molecules at the minor groove of the nucleotide, and C70, SWNT, and GQD bind to the dsDNA molecules at the hydrophobic ends. Estimated interaction energy implies that van der Waals force may mainly contribute to the mechanisms for the dsDNA-C60, dsDNA-C70, and dsDNA-SWNT interactions and electrostatic force may contribute considerably to the dsDNA-DWNT, dsDNA-GQD, and dsDNA-GOQD interactions. On the basis of the results from large-scale MD simulations, it was found that the presence of the dsDNA enhances the dispersion of C60, C70, and SWNT in water and has a slight impact on DWNT, GQD, and GOQD.

Axisymmetric vibration of SWCNTs in water with arbitrary chirality based on nonlocal anisotropic shell model

The axisymmetric vibration of three kinds of zigzag, armchair and chiral single-walled carbon nanotubes (SWCNTs) in water is studied in the paper based on the nonlocal anisotropic shell model. The present model is justified compared with the existing experimental observation and available data in literature. It is shown that for the tubes with the same diameter, the radial breathing frequencies from lower to upper limits are zigzag, chiral and armchair tubes, respectively. However, the difference in frequency diminishes with the increase of diameter. Furthermore, we found that the axisymmetric radial, longitudinal and torsional vibrational frequencies of SWCNTs are mainly sensitive to the values of radius and the scale coefficient, but cannot be substantially changed by their atomic structure. Moreover, we can get that the local shell model for CNT analysis would lead to an overprediction of the vibrational frequencies of almost all modes. So the nonlocal isotropic continuum models are practical in analyzing CNTs of large geometric sizes. Finally, the results show that the effects of fluid motion surrounding CNTs can be ignored for the large wave numbers.

Effects of Hydroxylated Carbon Nanotubes on the Aggregation of Aβ16–22 Peptides: A Combined Simulation and Experimental Study

The pathogenesis of Alzheimer’s disease (AD) is associated with the aggregation of amyloid-β (Aβ) peptides into toxic aggregates with β-sheet character. In a previous computational study, we showed that pristine single-walled carbon nanotubes (SWCNTs) can inhibit the formation of β-sheet-rich oligomers in the central hydrophobic core fragment of Aβ (Aβ16–22). However, the poor solubility of SWCNTs in water hinders their use in biomedical applications and nanomedicine. Here, we investigate the influence of hydroxylated SWCNT, a water-soluble SWCNT derivative, on the aggregation of Aβ16–22 peptides using all-atom explicit-water replica exchange molecular dynamics simulations. Our results show that hydroxylated SWCNTs can significantly inhibit β-sheet formation and shift the conformations of Aβ16–22 oligomers from ordered β-sheet-rich structures toward disordered coil aggregates. Detailed analyses of the SWCNT-Aβ interaction reveal that the inhibition of β-sheet formation by hydroxylated SWCNTs mainly results from strong electrostatic interactions between the hydroxyl groups of SWCNTs and the positively charged residue K16 of Aβ16–22 and hydrophobic and aromatic stacking interactions between SWCNTs and F19 and F20. In addition, our atomic force microscopy and thioflavin T fluorescence experiments confirm the inhibitory effect of both pristine and hydroxylated SWCNTs on Aβ16–22 fibrillization, in support of our previous and present replica exchange molecular dynamics simulation results. These results demonstrate that hydroxylated SWCNTs efficiently inhibit the aggregation of Aβ16–22; in addition, they offer molecular insight into the inhibition mechanism, thus providing new clues for the design of therapeutic drugs against amyloidosis.

Light-independent reactive oxygen species (ROS) formation through electron transfer from carboxylated single-walled carbon nanotubes in water.

Promising developments in application of carbon nanotubes (CNTs) have raised concern regarding potential biological and environmental effects upon their inevitable release to the environment. Although some CNTs have been reported to generate reactive oxygen species (ROS) under light, limited information exists on ROS generation by these materials in the dark. In this study, generation of ROS was examined, initiated by electron transfer from biological electron donors through carboxylated single-walled carbon nanotubes (C-SWCNT) to molecular oxygen in water in the dark. In the presence of C-SWCNT, the oxidation of NADH (β-nicotinamide adenine dinucleotide, reduced form) and DTTre (DL-dithiothreitol, reduced form) was confirmed by light absorbance shifts (340 nm to 260 nm during oxidation of NADH to NAD(+), and increased light absorbance at 280 nm during oxidation of DTTre). Production of superoxide anion (O2(•-)) was detected by its selective reaction with a tetrazolium salt (NBT(2+)), forming a formazan product that is visible at 530 nm. A modified acid-quenched N,N-diethyl-p-phenylenediamine (DPD) assay was used to measure the accumulation of H2O2 in C-SWCNT suspensions containing O2 and NADH. In the same suspensions (i.e., containing C-SWCNT, NADH, and O2), pBR322 DNA plasmid was cleaved, although •OH was not detected when using •OH scavenging molecular probes. These results indicate that the oxidation of electron donors by C-SWCNT can be a light-independent source of ROS in water, and that electron shuttling through CNTs to molecular oxygen may be a potential mechanism for DNA damage by this specific CNT and potentially other carbon-based nanomaterials.

Mechanisms of carbon nanotube aggregation and the reversion of carbon nanotube aggregates in aqueous medium.

Single-walled carbon nanotubes (SWCNTs) dispersed in aqueous medium have many potential applications in chemistry, biology, and medicine. Reversible aggregation of SWCNTs dispersed in water has been frequently reported, but the mechanisms behind are not well understood. Here we show that SWCNTs dispersed into aqueous medium assisted by various charged molecules can be reversibly aggregated by a variety of electrolytes with two distinct mechanisms. Direct binding of counterions to SWCNTs leads to aggregation when the surface charge is neutralized from 74 to 86%. This aggregation is driven by electrostatic instead of van der Waals interactions, thus showing similarity to that of DNA condensation induced by multivalent cations. Sequestration of counterions by chelating reagents leads to the redispersion of SWCNT aggregates. In contrast to various metal ions, polyelectrolytes have the unique ability to induce SWCNT aggregation by bridging between individual SWCNTs. Aggregation through the latter mechanism can be engineered to be reversible by exploiting various mechanisms of chain breaking, including reduction of disulfide bond in the polymer chain, and the cleavage action of proteolytic enzymes. These findings clarify the mechanisms of SWCNT aggregation, and have broad implications in various applications of SWCNTs in water.

Modified SWCNTs with Amphoteric Redox and Solubilizing Properties

A complementary double-covalent functionalization of single-wall carbon nanotubes (SWCNTs) that involves both solubilizing ionic liquids and electroactive moieties is reported. Our strategy is a simple and efficient methodology based on the stepwise functionalization of the nanotube surface with two different organic moieties. In a first instance, oxidized SWCNTs are amidated with ionic liquid precursors, and further treated with n-butyl bromide to afford SWCNTs functionalized with 1-butylimidazolium bromide. This approach allows tuneable polarity induced by anion exchange, which has an effect on the relative solubility of the modified SWCNTs in water. Subsequently, a 1,3-dipolar cycloaddition reaction was performed to introduce the electron-acceptor 11,11,12,12-tetracyano-9,10-anthra-para-quinodimethane (TCAQ) unit on the SWCNTs. Furthermore, to evaluate the influence of the functional group position, the TCAQ electroactive molecule was anchored through an esterification reaction onto previously oxidized SWCNTs, followed by the Tour reaction to introduce the ionic liquid functions. IR and Raman spectroscopies, thermogravimetric analysis (TGA), UV/Vis/NIR spectroscopy, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) were employed and clearly confirmed the double-covalent functionalization of the SWCNTs.

Effective Nondestructive Purification of Single-Walled Carbon Nanotubes Based on High-Speed Centrifugation with a Photochemically Removable Dispersant

A purification method for raw single-walled carbon nanotubes (SWCNTs) without damage to their intrinsic structures has been desired in many applications. We investigated the purification of SWCNTs based on high-speed centrifugation of water-dispersed SWCNTs using the photoreactive dispersant we previously investigated. SWCNTs wrapped with the dispersant were separated from impurities, such as an amorphous carbon and metal particles by centrifugation, similarly to conventional physical purification using surfactants. In contrast to general surfactants that form micelles to disperse SWCNTs in aqueous solutions, the photoreactive dispersant did not form micelles. Therefore, an excess amount of the dispersant, which did not adsorb onto the SWCNT surfaces, was removable by dialysis of the supernatant. Since the amount of the dispersant was minimized by dialysis, we tuned the UV-irradiation time to eliminate the dispersibility of SWCNTs in water to as low a value as ∼2 h. The SWCNT precipitates were collected, ...

The Environmental Effect on the Dynamical Behaviors of Single-Walled Carbon Nanotube in Water

The paper investigates the dynamical behaviors of single-walled carbon nanotube (SWCNT) in water, focusing on the effect of external environment (i.e., water) on SWCNT. The SWCNT-water system comprises three constituent parts, that is, the SWCNT, the absorbed layer of water molecules, and the water flow around the water layer. The SWCNT and the absorbed layer of water are modeled as two-layer thin shells coupled via the interlayer vdW interaction, and the water surrounding the absorbed water layer is considered as the potential flow. The numerical simulations show that the vdW interaction is responsible for an upshift in the frequency of the SWCNT and preserving the stability of system. Flow velocity has almost no effect on the natural frequency of SWCNT, while being quite significant for destabilizing of the CNT-fluid system. In addition, the effect of wavenumber on the coupled system is also considered. The study not only greatly reduces simulation time but also provides a new model to explain the experimental observation available in particular cases.

Preparation and biological activity of a paclitaxel-single-walled carbon nanotube complex

Single-walled carbon nanotubes (SWCNTs) have unique transmembrane abilities. The huge superficial area and abundance of π electrons confer SWCNTs perfect absorptive capability toward proteins, nucleates, and many drugs. These characteristics make SWCNTs a new and efficient drug carrier. The purpose of this study was to disperse SWCNTs in water and have paclitaxel absorbed onto them in order to construct an asparagine-glycine-arginine (NGR)-SWCNT-Paclitaxel complex as a targeting nanoparticle system. The NGR-SWCNT-Paclitaxel complex was systematically studied, and analytical methods, including spectrophotometry for SWCNTs and high-performance liquid chromatography for paclitaxel, were employed. The preparation and the prescription of the NGR-SWCNT-Paclitaxel complex lyophilized powder were investigated. MCF-7 cancer cells, Sprague-Dawley rats, and S180 tumor-bearing mice were used as experimental subjects to evaluate the in vitro and in vivo activity of NGR-SWCNT-Paclitaxel complex dispersion. The complex dispersion showed obvious inhibition activity against MCF-7 cancer cells. Within 1 h, the NGR-SWCNT-Paclitaxel complex could be transferred to cells, and sustained the release of drugs. In addition, the tumor and liver targeting and improved therapeutic effects of the NGR-SWCNT-Paclitaxel complex were confirmed.

Compressive characteristics of single walled carbon nanotube with water interactions investigated by using molecular dynamics simulation

Abstract The elastic properties of single walled carbon nanotube (SWCNT) with surrounding water interactions are studied using molecular dynamics simulation technique. The compressive loading characteristic of carbon nanotubes (CNTs) in a fluidic medium such as water is critical for its role in determining the lifetime and stability of CNT based nano-fluidic devices. In this paper, we conducted a comprehensive analysis on the effect of geometry, chirality and density of encapsulated water on the elastic properties of SWCNT. Our studies show that defect density and distribution can strongly impact the compressive resistance of SWCNTs in water. Further studies were conducted on capped SWCNTs with varying densities of encapsulated water, which is necessary to understand the strength of CNT as a potential drug carrier. The results obtained from this paper will help determining the potential applications of CNTs in the field of nano-electromechanical systems (NEMS) such as nano-biological and nano-fluidic devices.

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.

Lentinan greatly enhances the dispersibility of single-walled carbon nanotubes in water and decreases the cytotoxicity

Abstract Single-chain Lentinan (s-LNT) was found to efficiently disperse single-walled carbon nanotubes (SWNT) in water. Raman spectroscopy, atomic force aicroscopy (AFM), scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), and energy dispersive X-ray spectroscopy demonstrated the formation of SWNTs/s-LNT composites through hydrogen-bonding and hydrophobic interactions between SWNTs and s-LNT. When adding DMSO or NaOH into the aqueous solution of SWNTs/s-LNT, SWNTs precipitated out, suggesting that hydrogen-bonding was broken and SWNTs were released from the composites. More interestingly, helical wrapping structures of s-LNT on the surface of SWNTs were observed by AFM and HRTEM. It can be explained as follows: the water-soluble s-LNT chains wrapped on the surface of hydrophobic SWNTs in a helical manner, endowing the water-solubility of SWNTs. Moreover, the SWNTs/s-LNT remarkably improved the cell viability in contrast to SWNTs in vitro test. This work provided an alternative method by which hydrophobic SWNTs were successfully dispersed in water by the water-soluble beta-glucan LNT in a helical wrapping manner, which also enlarged the applications of LNT.