Optical Properties Of Single-walled Carbon Nanotubes Research Articles

Stochastic Formation of Quantum Defects in Carbon Nanotubes.

Small perturbations in the structure of materials significantly affect their properties. One example is single wall carbon nanotubes (SWCNTs), which exhibit chirality-dependent near-infrared (NIR) fluorescence. They can be modified with quantum defects through the reaction with diazonium salts, and the number or distribution of these defects determines their photophysics. However, the presence of multiple chiralities in typical SWCNT samples complicates the identification of defect-related emission features. Here, we show that quantum defects do not affect aqueous two-phase extraction (ATPE) of different SWCNT chiralities into different phases, which suggests low numbers of defects. For bulk samples, the bandgap emission (E11) of monochiral (6,5)-SWCNTs decreases, and the defect-related emission feature (E11*) increases with diazonium salt concentration and represents a proxy for the defect number. The high purity of monochiral samples from ATPE allows us to image NIR fluorescence contributions (E11 = 986 nm and E11* = 1140 nm) on the single SWCNT level. Interestingly, we observe a stochastic (Poisson) distribution of quantum defects. SWCNTs have most likely one to three defects (for low to high (bulk) quantum defect densities). Additionally, we verify this number by following single reaction events that appear as discrete steps in the temporal fluorescence traces. We thereby count single reactions via NIR imaging and demonstrate that stochasticity plays a crucial role in the optical properties of SWCNTs. These results show that there can be a large discrepancy between ensemble and single particle experiments/properties of nanomaterials.

First Principles Study on Electronic and Optical Properties of Single Walled Carbon Nanotube for Photonics Application

Recent research works on single-walled carbon nanotube (SWCNT) based material has witnessed a great technological importance in photonic applications due to their unique optical characteristics. Present work aims to employ theoretical first principles study to explore the electronic and optical properties of SWCNT in the form of armchair nanotube. The theoretical simulation is done by using density functional theory (DFT) as implemented in the CASTEP computer code. Similar to almost gapless nature of graphene, formation of Fermi level of a relaxed SWCNT structure is found to be at a value approaching zero. The calculated electronic band structure shows a direct band gap of 0.259 eV with Dirac cone form between conduction and valence band. The optical spectrum shows a variation of real and imaginary of dielectric function with inter-band transition taking place along with frequency of the incident light. The absorption spectrum exhibits a significant degree of anisotropic characteristic with almost transparent nature ranging from near infrared to ultraviolet energy range. These optical spectra show excellent nonlinear optical features which remark the suitability in optoelectronic applications.

Optical Property Tuning of Single-Wall Carbon Nanotubes by Endohedral Encapsulation of a Wide Variety of Dielectric Molecules.

Specific and tunable modification to the optical properties of single-wall carbon nanotubes (SWCNTs) is demonstrated through direct encapsulation into the nanotube interior of guest molecules with widely varying static dielectric constants. Filled through simple ingestion of the guest molecule, each SWCNT population is demonstrated to display a robust modification to absorbance, fluorescence, and Raman spectra. Over 30 distinct compounds, covering static dielectric constants from 1.8 to 109, are inserted in large diameter SWCNTs (d = 1.104-1.524 nm) and more than 10 compounds in small diameter SWCNTs (d = 0.747-1.153 nm), demonstrating that the general effect of filler dielectric on the nanotube optical properties is a monotonic energy reduction (red-shifting) of the optical transitions with increased magnitude of the dielectric constant. Systematic fitting of the two-dimensional fluorescence-excitation and Raman spectra additionally enables determination of the critical filling diameter for each molecule and distinguishing of overall trends from specific guest-host interactions. Comparisons to predictions from existing theory are presented, and specific guest molecule/SWCNT chirality combinations that disobey the general trend and theory are identified. A general increase of the fluorescence intensity and line narrowing is observed for low dielectric constants, with long linear alkane filled SWCNTs exhibiting emission intensities approaching those of empty SWCNTs. These results demonstrate an exploitable modulation in the optical properties of SWCNTs and provide a foundation for examining higher-order effects, such as due to nonbulk-like molecule stacking, in host-guest interactions in well-controlled nanopore size materials.

Dispersion of Single-Walled Carbon Nanotubes in Biocompatible Environments

The unique physical and chemical properties of carbon nanotubes (CNTs), including SWCNTs (single-walled carbon nanotubes), allow their applications in many fields, including biomedicine. The optical properties of SWCNTs are attractive for application in the field of nanobiotechnology compared to MWCNTs (multi-walled carbon nanotubes). An important objective of SWCNT application for biomedical purposes is obtaining homogenous dispersions characterized by bioavailability and biocompatibility. The possibility of obtaining homogenous dispersions of different types of SWCNTs in biocompatible media for further use in different biomedical experiments and applications has been investigated. The sizes of SWCNT agglomerates in prepared dispersions were measured by the method of dynamic light scattering; bioavailability was studied by dark field microscopy in BEAS-2B bronchial epithelium cells. The dispersions were analyzed for the presence of bacterial contamination. Biocompatible and bioavailable dispersions have been obtained on the basis of cell culture media and 1% bovine serum albumin, which can be used in experiments on assessing the safety of SWCNTs at biological objects but have a number of limitations in the field of biomedicine. Dispergents based on lung surfactant components, which could be used in biomedical applications (DPPC and Survanta®), did not show efficency.

In vitro and in vivo evaluation of antitumor drug-loaded aptamer targeted single-walled carbon nanotubes system.

A multifunctional tumor-targeting drug delivery system employing single-walled carbon nanotubes (SWCNT) as drug carriers, AS1411 as targeting ligand and doxorubicine (DOX) as a model chemotherapy drug was constructed. Firstly, SWCNT were modified with F68 (4.0 mg/ml) by ultrasonic dispersing technology due to the action of hydrophobic force and Van der Waals force, endowing SWCNT water dispersions and biocompatibility. Meanwhile, DOX could be easily absorbed on the surface of SWCNT by the π-π stacking, electrostatic adsorption and hydrophobic interactions. Finally, AS1411 was attached to the surface of DOX-SWCNT by the π-π stacking and electrostatic adsorption to obtain a tumor-targeting delivery system. Cellular uptake, anti-tumor effect in vitro and in vivo, cell cycle and apoptosis and biodistribution of AS1411-DOX-SWCNT were investigated, compared with the DOX solution. This AS1411-mediated DOX-loaded SWCNT (AS1411-DOX-SWCNT) delivery system not only retained both optical properties of SWCNT and cytotoxicity of DOX but also could accumulate in tumors, which facilitated combination of chemotherapy and photothermal therapy. AS1411-DOX-SWCNT could effectively promote DOX cellular uptake and then increase intracellular accumulation as a targeting delivery system. AS1411-DOX-SWCNT by NIR laser excited could trigger S phase arrest and the late stage apoptotic on PC3 cancer cells. The investigation in vivo further confirmed that this system possessed higher tumor targeting capacity and antitumor efficacy than DOX, especially with NIR laser irradiation.

Confinement in single walled carbon nanotubes investigated by spectroscopic ellipsometry

Thick films of single walled carbon nanotubes (SWCNTs) with different diameter and chirality distributions are characterized by combining transmission electron microscopy and spectroscopic ellipsometry. The dependence of the dielectric function with the increase of the SWCNT diameter occurs with a drastic redshift of the S11, S22 and M11 transition energies. The transfer integral parameter γ0 of SWCNT is also evaluated and analyzed. We demonstrate that parts of the optical properties of SWCNTs are attributed to a one dimensional confinement effect.

Single-walled carbon nanotubes mediated targeted tamoxifen delivery system using aspargine-glycine-arginine peptide

An aspargine-glycine-arginine (NGR) peptide modified single-walled carbon nanotubes (SWCNTs) system, developed by a simple non-covalent approach, could be loaded with the anticancer drug tamoxifen (TAM). This TAM-loaded NGR modified SWCNTs (TAM/NGR-SWCNTs) not only retained both optical properties of SWCNTs and cytotoxicity of TAM, but also could accumulate in tumors and enter into 4T1 cells, which facilitated combination chemotherapy with photothermal therapy in one targeting system. Enhanced cellular uptake, antitumor effect and cell apoptosis of TAM/NGR-SWCNTs on 4T1 cells were observed in vitro, compared with the TAM solution, TAM/SWCNTs and photothermal therapy alone. In vivo investigation of TAM/NGR-SWCNTs in tumor-bearing mice further confirmed that this system possessed much higher tumor targeting capacity and antitumor efficacy than the control, especially with the near-infrared-laser irradiation treatment. Moreover, it demonstrated negligible systematic toxicity through the histopathological analysis. All these results suggest TAM/NGR-SWCNTs are promising for high targeted efficiency and treatment efficacy and low side effects of future cancer therapy by synergistic effect of chemo-photothermal combination.

Photoluminescence studies on exciton photophysics in carbon nanotubes

Single-walled carbon nanotubes (SWNTs) are extremely thin cylinders of hexagonal carbon networks with diameters on the order of 1 nm. Over the past decade, optical properties of SWNTs, dominated by correlated electron–hole bound states known as excitons, have been intensively studied. The exciton photophysics of SWNTs is relevant to nearly all optical phenomena observed in SWNTs, and their detailed understanding is critical for the development of future optoelectronic devices using SWNTs. Here we review some interesting photophysics related to excitons in SWNTs, including fundamental features in optical absorption and photoluminescence spectra, effects of exciton–phonon interactions, anisotropic optical absorption and emission, effects of surrounding materials, radiative and nonradiative lifetimes, and diffusional exciton migration along SWNTs, which have been studied by continuous-wave and time-resolved optical spectroscopy.

Antitumor immunologically modified carbon nanotubes for photothermal therapy

An immunologically modified nanotube system was developed using an immunoadjuvant, glycated chitosan (GC), as surfactant of single-walled carbon nanotube (SWNTs). This SWNT-GC system not only retained both optical properties of SWNTs and immunological functions of GC, but also could enter cells due to the carrier properties of SWNTs. Cellular SWNTs induced thermal destruction of tumor cells when irradiated by a near-infrared laser and, at the same time, cellular GC could serve both as damage associated molecular pattern molecules (DAMPs) and pathogen associated molecular pattern molecules (PAMPs) to enhance the tumor immunogenicity and enhance the uptake and presentation of tumor antigens, leading to special antitumor response. Using this system and a 980 nm laser, we treated tumors, both in vitro and in vivo, and investigated the induced thermal and immunological effects. Laser + SWNT-GC afford a remarkable efficacy in suppressing tumor growth in animal cancer models, in many cases resulting in complete tumor regression and long-term survival. Mice successfully treated by Laser + SWNT-GC could establish resistance to tumor rechallenge. This system forms a multifunctional temporal-spatial continuum, which can synergize photothermal and immunological effects. The Laser + SWNT-GC could represent a promising treatment modality to induce systemic antitumor response through a local intervention, while minimizing the adverse side effects.

Optical Study on Electronic Transport Properties of Single-Walled Carbon Nanotubes at High Temperature

The transport properties of single-walled carbon nanotubes (SWNTs) above room temperature are studied in this work. The infrared optical properties of SWNTs were investigated to clarify their conduction mechanism at high temperature. We present reflectivity spectra of SWNT mats in the infrared region between 0.08 eV and 0.8 eV under Ar gas flow at temperatures between 330 K and 840 K. These spectra have the typical appearance of the metallic reflectivity. Examination within the framework of the Drude-Lorentz model was performed to work out the electric resistivity for each reflectivity spectrum. It was found that the resistivity of SWNTs increases superlinearly with increasing the temperature from 330 K to 690 K, which can be explained by the quasi-1D metallic term model very well. However, the resistivity at higher temperatures than 690 K exhibited the tendency of saturation and deviated from the quasi-1D metallic term model. This behavior could be attributed to the thermal excitation of free carriers in the semiconducting SWNTs included in the mats.

Optical spectroscopic studies of photochemically oxidized single-walled carbonnanotubes

We examined the time-dependent changes in the optical properties of single-walled carbonnanotubes which were consecutively oxidized by irradiation with vacuum ultraviolet light.It is demonstrated that photochemical oxidation is a mild and controllable method formanipulating the surface of nanotubes in order to convert their affinity from hydrophobicto hydrophilic by controlling the density of functional groups on their sidewalls withoutdestroying their tubular morphology.

Optically Sensing Additional Sonication Effects on Dispersed HiPco Nanotubes in Aerated Water

Ultrasonication is a necessary process to make single-walled carbon nanotubes (SWNTs) soluble in aqueous solution with surfactants such as sodium dodecyl sulfate (SDS). However, an understanding of the sonication effects on the electronic and optical properties of SWNTs in aqueous solution is still lacking. Here, we have observed that sonication-induced pH changes suppress the optical transitions of the first interband transition pair (S11) in the density of states of semiconducting SWNTs while other possible intermediates induced by sonication contribute less significantly to the observed spectral changes without the involvement of sonication-induced pH decrease. The suppressed S11 peaks can be restored by adding basic solution, suggesting that the lattice structure of SWNTs is undisrupted by the sonication used here. The absorbance of S11 peaks shows a nearly linear relationship with sonication-induced pH changes in the narrow pH range of 5.2 and 6.1. The results indicate that SDS-encased SWNTs may be used as an indicator for sonolysis-related applications.

Water-soluble and optically pH-sensitive single-walled carbon nanotubes from surface modification.

There is great interest in using single-walled carbon nanotubes (SWNTs) as nanoscale probes and sensors in biological electronics and optical devices because the electronic and optical properties of SWNTs are extremely sensitive to the surrounding environments. A well-controlled modification of SWNT surfaces may provide unique interfaces that are sensitive to the biological variables such as pH, glucose, various ions and proteins. In this paper, we report a facile chemical routine to prepare water-soluble SWNTs that still retain their van Hove singularities after acid oxidative treatment. The aqueous solutions (0.03-0.15 mg/mL) are stable for more than a month. The solubility in water for as-treated SWNTs with surfaces modified by carboxylate groups provides us with a unique opportunity to reveal the relationship of the SWNT electronic and optical properties with pH. Here we present the first observation that after surface modification with carboxylate groups, the optical absorption of the first interband transition of as-treated water-soluble semiconducting SWNTs reversibly responds to the pH change in aqueous solutions. Our results indicate that surface modification of SWNTs is a promising way for preparing chemically selective SWNT interfaces, which may open new exciting opportunities for various applications.