Walls Of Single-walled Carbon Nanotubes Research Articles

Shielding Effects Provide a Dominant Mechanism in J-Aggregation-Induced Photoluminescence Enhancement of Carbon Nanotubes.

The unique photophysical properties of single-walled carbon nanotubes (SWCNTs) exhibit great potential for bioimaging applications. This led to extensive exploration of photosensitization methods to improve their faint shortwave infrared (SWIR) photoluminescence. Here, we report the mechanisms of SWCNT-assisted J-aggregation of cyanine dyes and the associated photoluminescence enhancement of SWCNTs in the SWIR spectral region. Surprisingly, we found that excitation energy transfer between the cyanine dyes and SWCNTs makes a negligible contribution to the overall photoluminescence enhancement. Instead, the shielding of SWCNTs from the surrounding water molecules through hydrogen bond-assisted macromolecular reorganization of ionic surfactants triggered by counterions and the physisorption of the dye molecules on the side walls of SWCNTs play a primary role in the photoluminescence enhancement of SWCNTs. We observed 2 orders of magnitude photoluminescence enhancement of SWCNTs by optimizing these factors. Our findings suggest that the proper shielding of SWCNTs is the critical factor for their photoluminescence enhancement, which has important implications for their application as imaging agents in biological settings.

(Invited) Single-Walled Carbon Nanotubes As Optical Probes for Imaging and Biosensing

Single-walled carbon nanotubes (SWCNT) are exceptionally photostable fluorophores that emit in the near-infrared range. Their novel physical and chemical properties make them particularly appealing as optical probes for microscopy and spectroscopy. The π-electron rich side wall of SWCNT allows various biopolymers to be conjugated through π-π stacking, enabling novel applications in biology and medicine. In particular, oligonucleotides (DNA or RNA) have been widely used to functionalize SWCNT due to its specific base-pairing properties and programmability. Here we demonstrate the use of DNA-SWCNT hybrid nanomaterial in fundamental biophysics research and biomolecular sensing applications. In the first system, we show SWCNT can be used as a photo-stable imaging probe for optically tracking DNA walker's transport characteristics. DNA walkers are synthetic nanosystems that exploit the structural specificity and functional diversity of oligonucleotides to mimic intracellular protein motors. We integrated a DNA walker system onto SWCNT and demonstrated transportation of quantum dots along SWCNT track. We used localization microscopy and single-particle tracking to record the displacement time series of multiple walkers, which is then used to build the statistical distribution of speed, displacement and walking turnover time. The statistical characteristics of the system help extract time averaged and ensemble averaged walker kinetics, which provide biochemical and biophysical insights about the system. In the second system, we demonstrate using aptamer-SWCNT as a novel sensor architecture for biomolecular detection. We non-covalently functionalized SWCNT with porphyrin binding aptamers, which retains aptamer's target specificity and nanotube's optical property. We discovered the photoluminescence of aptamer-SWCNT is selectively quenched upon binding to heme, an iron-containing porphyrin present in diverse biological processes. The aptamer-SWCNT complex also serves as a quencher for the intrinsic fluorescence of porphyrins. We propose the two optical transduction signatures are induced by specific binding of aptamer to heme and non-specific adsorption of other porphyrin species on the side wall of SWCNT. Using these two properties, we developed a sensing mechanism for four porphyrin species present in the biosynthetic pathway, and demonstrated multiplexed porphyrin detection in blood plasma. Our work shows that SWCNT is a useful optical material for both fundamental biomolecular engineering research and biomedical applications.

Morphology Studies of SWCNT Dispersed in Conducting Polymer as Potential Sensing Materials

Novel electronic nanomaterial, the carbon nanotube (CNT) has emerged in many sensor applications as such its state dispersion has considerable importance to ensure the sustainability of its electronic properties. In this paper, we reported a state of art conductivity mapping on nanostructure surface of single walled carbon nanotubes (SWCNT) and poly(3-hexylthiophene-2,5-diyl), (P3HT) as potential sensing film. This composite is proposed to give selective analyte anchoring across the film as well as improved carrier mobility. The easy solution processing method was chosen to produce non-covalently wrapped conducting polymer onto the surface of SWCNT. We successfully observed high resolution images of the SWCNT walls that indicated increase of the thickness due to polymer wrapping. The image obtained from conductivity atomic force microscopy (CAFM) show the film’s electrical distribution that correlated with the observed nanostructure of film. Supporting optical characteristics of the nanocomposite obtained from UV-Vis spectroscopy and Raman spectroscopy discussed the morphology of the polymer wrapping and the state of dispersion of the polymer and the nanotubes. It is hypothesized the filament structures made by P3HT/SWCNT can give better sensing performance due to modification of π-π electronic band of SWCNT.

Effective Photodynamic Therapy for Colon Cancer Cells Using Chlorin e6 Coated Hyaluronic Acid-Based Carbon Nanotubes.

Colon cancer is the third major cancer contributor to mortality worldwide. Nanosized particles have attracted attention due to their possible contribution towards cancer treatment and diagnosis. Photodynamic therapy (PDT) is a cancer therapeutic modality that involves a light source, a photosensitizer and reactive oxygen species. Carbon nanotubes are fascinating nanocarriers for drug delivery, cancer diagnosis and numerous potential applications due to their unique physicochemical properties. In this study, single walled carbon nanotubes (SWCNTs) were coupled with hyaluronic acid (HA) and chlorin e6 (Ce6) coated on the walls of SWCNTs. The newly synthesized nanobiocomposite was characterized using ultraviolet-visible spectroscopy, Fourier transform electron microscopy (FTIR), X-ray diffraction analysis (XRD), particle size analysis and zeta potential. The loading efficiency of the SWCNTs-HA for Ce6 was calculated. The toxicity of the nanobiocomposite was tested on colon cancer cells using PDT at a fluence of 5 J/cm2 and 10 J/cm2. After 24 h, cellular changes were observed via microscopy, LDH cytotoxicity assay and cell death induction using annexin propidium iodide. The results showed that the newly synthesized nanobiocomposite enhanced the ability of PDT to be a photosensitizer carrier and induced cell death in colon cancer cells.

Hybrid materials of carbon nanotubes with fluoroalkyl- and alkyl-substituted zinc phthalocyanines

In this work, hybrid materials of single-walled carbon nanotubes (SWCNT) noncovalently functionalized with fluoroalkyl- (SWCNT/ZnPc-CF) and alkyl- (SWCNT/ZnPc-CH) substituted zinc(II) phthalocyanines were prepared. The effect of fluorination of the substituents in phthalocyanine macrocycle on the functionalization degree of carbon nanotubes and sensor response to ammonia was investigated. It was shown that the type of substituents in the phthalocyanine macrocycle showed noticeable effect both on the degree of functionalization of carbon nanotubes and on the sensing performance of the investigated hybrids. The amount of phthalocyanine molecules adsorbed on SWCNT walls was shown to be 1.5 times higher in the SWCNT/ZnPc-CH hybrid. The SWCNT/ZnPc-CF layer exhibited 2 times less chemiresistive sensor response to ammonia than SWCNT/ZnPc-CH, while its sensor response was more stable at 70% relative humidity.

Large-scale DFT simulation of quinone molecules encapsulated in single-walled carbon nanotube for novel Li-ion battery cathode

A system of quinone molecules encapsulated in single-walled carbon nanotubes (SWCNTs) has been proposed as a next-generation cathode material for rechargeable batteries [Y. Ishii et al., Phys. Chem. Chem. Phys. 18 (2016) 10411–10418]. We use density functional theory (DFT) to theoretically investigate (i) the electronic and structural states of SWCNT-encapsulated quinone with or without Li and (ii) the Li insertion and extraction dynamics in the system. Substantial electron transfer from the quinone molecules to the SWCNT is thereby observed. This electron transfer stabilizes the positively charged quinone molecules in the negatively charged SWCNT through Coulomb attraction and decreases the electronic band gap for the SWCNT with semiconductor chirality. In the case of 9,10-phenanthrenequinone (PhQ), we observe that the cross-sectional shape of the SWCNT changes substantially in the relaxed state depending on the extent of Li insertion: the SWCNT exhibits a circular cylinder shape when no Li is present, whereas it is flattened upon sufficient Li insertion. These SWCNT shapes well reflect the aggregated shapes of PhQ molecules, which depend on the amount of Li inserted. As for the Li insertion and extraction dynamics, we find that the Li atoms can take either of two paths: one is along the SWCNT wall, and the other involves hopping on the PhQ molecules and/or the sites where the C atoms of the SWCNT and the O atoms of PhQ molecules contact each other. The Li-transfer rate on the SWCNT wall is large; hence, the hopping is the rate-limiting step.

Field emission enhancement of PbS colloidal quantum dot-decorated single-walled carbon nanotubes

Herein, a simple and effective PbS colloidal quantum dot (CQD) decoration method for single-walled carbon nanotube (SWNT) is demonstrated. By dipping the SWNT film into a CQD dispersion followed by a solid-state ligand exchange, CQDs were successfully decorated onto the wall of SWNT without compromising a narrow size distribution. Spectroscopic studies suggested that (1) the CQD decoration and subsequent ligand exchange process did not alter the chemical nature of the SWNT framework and (2) there was a charge (electron) transfer process from the PbS CQD to the SWNT. Field emission (FE) characteristics of the CQD-decorated SWNT films revealed that FE enhancement was indeed established from SWNTs with a moderate degree of CQD decoration, while those with excessive decoration (coating) exhibited notable FE suppression. Horizontal current-voltage measurements with perpendicular-directional external electric field modulation suggested that electron supplement of SWNT from PbS CQD was pronounced as the amount of decorated CQDs increased. Based on the experimental results, we proposed a new mechanism demonstrating FE enhancement of a CQD/SWNT heterostructure.

Fast Photo-Chemical Synthesis of Fluorescent Defects on Carbon Nanotubes

Solitary fluorescent defects on single-walled carbon nanotubes (SWCNTs) have been shown to emit short-wave infrared (SWIR) single photons at room-temperature, enabling applications for quantum communication or cryptography. In addition, the new emission band at lower energy allows better resolution and contrast of in vivo images because lower scattering and lower autofluorescence can be achieved by shifting both excitation and emission into SWIR. A more reliable and scalable method for synthesizing fluorescent defects on SWCNTs is needed for translating from fundamental studies to practical applications. Here, we introduce a fast and reproducible method for creating oxygen-doped fluorescent defects on SWCNTs. The maximum intensity of the defect emission is reached within 40 secs, which is at least 24 times faster than reported values. The oxygen source is provided by the photo-dissociation of the hypochlorite ions and the doping occurs by direct attachment of the oxygen atom onto the SWCNT wall. This method produces minimum non-fluorescent defects, and more than 95% of the resulting SWCNTs contain fluorescent defects. We also built a high-throughput flow reactor to synthesize the O-doped SWCNTs at scale and used them for imaging vascular and lymphatic systems.

Molecular modeling investigation on mechanism of phenol removal from aqueous media by single- and multi-walled carbon nanotubes

In this work, results of molecular and quantum chemical modeling are reported for the mechanism of phenol removal by single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs). First, the lowest energy sites of SWNTs and MWNTs were investigated using quantum mechanics/molecular mechanics methods by utilization Adsorption site locator module of Material Studio software. Then, the equilibrium adsorption capacities of SWNT and MWNTs (with 2 up to 19 walls) were calculated using the conductor-like screening models with segmented activity coefficients (COSMO-SAC) model following the local pseudo-thermodynamic equilibrium at the interface of carbon nanotubes and phenol-containing effluent. It was revealed that the MWNTs with 12 walls are mainly responsible for phenol removal as higher and better interactions were obtained which is coherent with a major probability of these MWNTs. In addition, the removal mechanism in SWNTs was found to be entirely physical trapping within the SWNT walls, while in MWNTs a combination of lateral surface adsorption and negligible physical trapping within MWNT walls was found as both the inner diameter and distance (gap) between walls are smaller than the size of phenol molecules. The contribution of adsorption onto the lateral surface increases as the number of walls increases while the contribution of physical trapping fades. The equilibrium adsorption capacity was calculated for phenol/water loading fractions of 0.01–0.33. Correlation of equilibrium adsorption capacities and phenol concentrations resulted in relationships as lnqe = 0.464 × ln Ce + 0.9596 and lnqe = 0.4979 × ln Ce + 0.9696, respectively for SWNTs and MWNTs from water effluents containing phenol of Ce concentration with regression value R2 > 0.99.

Modelling of the Usefulness of Carbon Nanotubes as Antiviral Compounds for Treating Alzheimer Disease

The new generations of nano-devices successfully apply with great promise as drug carriers in the treatment of different diseases. The proposed model aims to determine the pharmacological targets and evaluate the bio-safety of usefulness of carbon nanotube conjugated with two different antiviral compounds, Acetylcholine and Ravastigmine, for treating Alzheimer disease. We also obtain the medicinal model mathematically to evaluate the interaction energy arising from encapsulation of each antiviral compound inside the single-walled carbon nanotube. Acetylcholine is modelled as two-connected spheres, while Ravastigmine has two possible structures which are an ellipsoid and cylinder, all interacting with the interior wall of single-walled carbon nanotubes with variant radii rc . Our calculations show that the single-walled carbon nanotube of radius rc greater than 3.391 Å that will accept both drugs which are quite closer to the recent findings.

Effect of covalent and non-covalent linking of zinc(II) phthalocyanine functionalised carbon nanomaterials on the sensor response to ammonia

In this work, a comparative study of the sensor response of single walled carbon nanotubes (SWCNTs) and reduced graphene oxide (rGO) covalently and non-covalently functionalised with1-[N-(2-ethoxyethyl)-4-pentynamide]-8(11),15(18),22(25)-tris-{2-[2-(2-ethoxyethoxy) ethoxy]-1-[2-((2-ethoxy ethoxy)-ethoxy)methyl]ethyloxy}zinc(II) phthalocyanine (ZnPc) to ammonia is carried out. It was shown that in the case of SWCNT-based materials both covalent and non-covalent functionalisation with zinc(II) phthalocyanine leads to the increase of the sensor response toward NH3, while functionalisation of reduced graphene oxide causes a decrease in the response. At the same time both covalent and non-covalent linking of zinc(II) phthalocyanine leads to twofold decrease of the sensor recovery times. The sensor response of the carbon nanomaterial (single walled carbon nanotubes or reduced graphene oxide) hybrids covalently functionalised with zinc(II) phthalocyanine is several times higher than in the case of non-covalent linking of zinc(II) phthalocyanine to these nanomaterials, which is in good correlation with the number of zinc(II) phthalocyanine molecules adsorbed onto the SWCNT and rGO walls.

Curvature dependence of single-walled carbon nanotubes for SO2 adsorption and oxidation

Porous carbon-based catalysts showing high catalytic activity for SO2 oxidation to SO3 is often used in flue gas desulfurization. Their catalytic activity has been ascribed in many publications to the microporous structure and the effect of its spatial confinement. First principles method was used to investigate the adsorption and oxidation of SO2 on the inner and outer surface of single-walled carbon nanotubes (SWCNTs) with different diameters. It is interesting to found that there is a direct correlation: the barrier for the oxidation O_SWCNT+SO2→SO3+SWCNT monotonically decreases with the increase of SWCNTs’ curvature. The oxygen functional located at the inner wall of SWCNTs with small radius is of higher activity for SO2 oxidation, which is extra enhanced by the spatial confinement effects of SWCNTs. These findings can be useful for the development of carbon-based catalysts and provide clues for the optimization and design of porous carbon catalysts.

Size-Dependent Structure Relations between Nanotubes and Encapsulated Nanocrystals.

The structural organization of compounds in a confined space of nanometer-scale cavities is of fundamental importance for understanding the basic principles for atomic structure design at the nanolevel. Here, we explore size-dependent structure relations between one-dimensional PbTe nanocrystals and carbon nanotube containers in the diameter range of 2.0-1.25 nm using high-resolution transmission electron microscopy and ab initio calculations. Upon decrease of the confining volume, one-dimensional crystals reveal gradual thinning, with the structure being cut from the bulk in either a <110> or a <100> growth direction until a certain limit of ∼1.3 nm. This corresponds to the situation when a stoichiometric (uncharged) crystal does not fit into the cavity dimensions. As a result of the in-tube charge compensation, one-dimensional superstructures with nanometer-scale atomic density modulations are formed by a periodic addition of peripheral extra atoms to the main motif. Structural changes in the crystallographic configuration of the composites entail the redistribution of charge density on single-walled carbon nanotube walls and the possible appearance of the electron density wave. The variation of the potential attains 0.4 eV, corresponding to charge density fluctuations of 0.14 e/atom.

In situ Raman spectroelectrochemical study of potential-induced molecular encapsulation of β-carotene inside single-walled carbon nanotubes

The effect of the electrochemical potential of single-walled carbon nanotubes (SWCNTs) on the encapsulation behavior of β-carotene inside the SWCNT cavities was investigated by in situ Raman spectroelectrochemistry. Prior to Raman measurement, the electrochemical behavior of β-carotene at SWCNT electrodes was investigated. Weak adsorption of β-carotene was observed, whereas at glassy carbon (GC) and highly oriented pyrolytic graphite (HOPG) electrodes, β-carotene showed diffusion-controlled reactions and was not adsorbed. Furthermore, a negative potential shift of the oxidation reaction of β-carotene was observed at the SWCNT surface compared with that at other carbon materials such as GC and HOPG. To remove the ends of SWCNTs to allow encapsulation of β-carotene and minimize damage of the side wall of SWCNTs, we used finely controlled potential oxidation method. Results of the in situ Raman measurements indicated that encapsulation of β-carotene into the SWCNT cavity occurred most smoothly when a potential of 0.3V (vs. Ag/Ag+) was applied to the SWCNTs. When the applied potential was >0.4V, the encapsulated β-carotene could be oxidized and decomposed through formation of cation radical and dication forms of β-carotene, even though the β-carotene was encapsulated in the SWCNTs. Applied potentials of –0.2~0.2V did not result in smooth encapsulation compared with that at 0.3V. Overall, we found that the encapsulation behavior of β-carotene in SWCNTs depended on the potential of the SWCNTs.

Cloaking by π‐electrons in the infrared

AbstractHybrid materials composed of single walled carbon nanotubes (SWCNTs) as hollow containers and small molecules as fillers possess intriguing physical and chemical properties. Infrared spectroscopy is a useful method in most cases to characterize hybrid systems; however, regardless of the type of small molecule encapsulated in the SWCNT, the IR spectrum of the hybrid system remains silent. The possible explanation involves the highly polarizable ‐electron system of the SWCNTs. Image charges induced in the SWCNT walls cancel out the transition dipole moment of the molecular vibrations resulting in the cloaking of the material inside the nanotube. To confirm the role of the delocalized ‐electron system in this process, insulating boron nitride nanotubes filled with were also investigated and found to be transparent to infrared radiation. We have also demonstrated the cloaking effect in two dimensions using a thin film of covered by single layer graphene. The significance of our results lies in the fact that the cloaking layer is a real material, not a metamaterial.

Origin of a Raman scattering peak generated in single-walled carbon nanotubes by X-ray irradiation and subsequent thermal annealing

We have found that a Raman scattering (RS) peak around 1870 cm−1 was produced by the annealing of the X-ray irradiated film of single-walled carbon nanotubes (SWNTs) at 450 oC. The intensity of 1870-cm−1 peak showed a maximum at the probe energy of 2.3 eV for the RS spectroscopy with various probe lasers. Both the peak position and the probe-energy dependence were almost identical to those of the one-dimensional carbon chains previously reported in multi-walled carbon nanotubes. Consequently, we concluded that the 1870-cm−1 peak found in the present study is attributed to carbon chains. The formation of carbon chains by the annealing at temperature lower than 500 oC is firstly reported by the present study. The carbon chains would be formed by aggregation of the interstitial carbons, which are formed as a counterpart of carbon vacancies by X-ray irradiation diffused on SWNT walls. The result indicates that the combination of X-ray irradiation and subsequent thermal annealing is a feasible tool for generating new nanostructures in SWNT.

Electrochemical Redox Switchable Dispersion of Single-Walled Carbon Nanotubes in Water.

We present a new, efficient approach to achieve superior dispersibility of single-walled carbon nanotubes (SWNTs) in water by integrating reversible host-guest interaction and π-π stacking. In this approach, β-cyclodextrin (β-CD) was first modified with a pyrene group to be adsorbed onto the wall of pristine SWNTs via π-π stacking, followed by further functionalization with ferrocene (Fc)-terminated water-soluble poly(ethylene glycol) (PEG) through supramolecular host-guest interaction between β-CD and Fc. Upon alternate electrochemical oxidative/reductive stimuli, the reversible host-guest pair enabled the PEG-Fc@Py-CD@SWNTs to exhibit switchable conversion between dispersion and aggregation states. Electric field controllable PEG-Fc@Py-CD@SWNTs with good reversibility and intact nanotube structure may find potential applications in selective screening of SWNTs, biosensors, and targeted drug delivery.

Van der Waals forces and confinement in carbon nanopores: Interaction between CH4, COOH, NH3, OH, SH and single-walled carbon nanotubes

Interactions between CH4, COOH, NH3, OH, SH and armchair (n,n)(n=4,7,14) and zigzag (n,0)(n=7,12,25) single-walled carbon nanotubes (SWCNTs) have been systematically investigated within the framework of dispersion-corrected density functional theory (DFT-D2). Endohedral and exohedral molecular adsorption on SWCNT walls is energetically unfavorable or weak, despite the use of C6/r6 pairwise London-dispersion corrections. The effects of pore size and chirality on the molecule/SWCNTs interaction were also assessed. Chemisorption of COOH, NH3, OH and SH at SWCNT edge sites was examined using a H-capped (7,0) SWCNT fragment and its impact on electrophilic, nucleophilic and radical attacks was predicted by means of Fukui functions.

Molecular dynamics simulation of non-covalent single-walled carbon nanotube functionalization with surfactant peptides

Non-covalent functionalized single-walled carbon nanotubes (SWCNTs) with improved solubility and biocompatibility can successfully transfer drugs, DNA, RNA, and proteins into the target cells. Theoretical studies such as molecular docking and molecular dynamics simulations in fully atomistic scale were used to investigate the hydrophobic and aromatic π–π-stacking interaction of designing four novel surfactant peptides for non-covalent functionalization of SWCNTs. The results indicated that the designed peptides have binding affinity towards SWCNT with constant interactions during MD simulation times, and it can even be improved by increasing the number of tryptophan residues. The aromatic content of the peptides plays a significant role in their adsorption in SWCNT wall. The data suggest that π–π stacking interaction between the aromatic rings of tryptophan and π electrons of SWCNTs is more important than hydrophobic effects for dispersing carbon nanotubes; nevertheless SWCNTs are strongly hydrophobic in front of smooth surfaces. The usage of aromatic content of peptides for forming SWCNT/peptide complex was proved successfully, providing new insight into peptide design strategies for future nano-biomedical applications.

Quasi free-standing one-dimensional nanocrystals of PbTe grown in 1.4 nm SWNTs

Here, we show successful filling of 1.4 nm single-walled carbon nanotubes (SWNT) with PbTe nanocrystals. The structure of one-dimensional PbTe in SWNT was determined using high-resolution transmission electron microscopy (HRTEM). The electronic structure of composites was studied by optical absorbance and Raman spectroscopies indicating no noticeable interaction of encapsulated PbTe with SWNT wall. Experimental data are supported by ab-initio calculations, showing non-zero density of states at the Fermi level of PbTe@SWNT(10,10) provided by both SWNT and PbTe states and thus metallic conductivity of the composite.