Molecular Potential Structures of Heat-Treated Single-Wall Carbon Nanohorn Assemblies

Carbon Nanomaterial Fluorescent Probes and Their Biological Applications

Fluorescent carbon nanomaterials have broadly useful chemical and photophysical attributes that are conducive to applications in biology. In this review, we focus on materials whose photophysics allow for the use of these materials in biomedical and environmental applications, with emphasis on imaging, biosensing, and cargo delivery. The review focuses primarily on graphitic carbon nanomaterials including graphene and its derivatives, carbon nanotubes, as well as carbon dots and carbon nanohoops. Recent advances in and future prospects of these fields are discussed at depth, and where appropriate, references to reviews pertaining to older literature are provided.

Bisphosphonate type-dependent cell viability suppressive effects of carbon nanohorn-calcium phosphate-bisphosphonate nanocomposites

In the process of bone metastasis, tumor cells spread to the bones to activate osteoclasts, which cause pathological bone resorption and destruction. Bisphosphonates (BPs) inhibit osteoclast activation to resorb bone, reducing bone pain and fracture. We previously developed a nanocomposite for potential localized treatment of bone metastasis by loading a BP compound, ibandronate, onto oxidized carbon nanohorns (OxCNHs), a next-generation drug carrier, using calcium phosphates (CaPs) as mediators to generate OxCNH-CaP-BP nanocomposites. The objective of the present study was to determine nanocomposite formation and biological properties of nanocomposites constructed from two BPs, zoledronate and pamidronate. In vitro tests using murine macrophages (RAW264.7 cells) and osteoclasts differentiated from RAW264.7 cells revealed that the resulting OxCNH-CaP-BP nanocomposites suppressed cell viability in a BP type-dependent manner and more effectively than OxCNHs or BPs alone. The mechanism for the potent and BP type-dependent suppression of cell viability by OxCNH-CaP-BP nanocomposites, based on their relative cellular uptake and reactive oxygen species generation, is also discussed. The present study supports the conclusions that BPs can be loaded onto OxCNHs using CaPs as mediators, and that OxCNH-CaP-BP nanocomposites are putative medicines for localized treatment of metastatic bone destruction.

Structural Study of Sulfur-Added Carbon Nanohorns

In the past few decades, nanostructured carbons (NCs) have been investigated for their interesting properties, which are attractive for a wide range of applications in electronic devices, energy systems, sensors, and support materials. One approach to improving the properties of NCs is to dope them with various heteroatoms. This work describes the synthesis and study of sulfur-added carbon nanohorns (S-CNH). Synthesis of S-CNH was carried out by modified chemical vapor deposition (m-CVD) using toluene and thiophene as carbon and sulfur sources, respectively. Some parameters such as the temperature of synthesis and carrier gas flow rates were modified to determine their effect on the properties of S-CNH. High-resolution scanning and transmission electron microscopy analysis showed the presence of hollow horn-type carbon nanostructures with lengths between 1 to 3 µm and, diameters that are in the range of 50 to 200 nm. Two types of carbon layers were observed, with rough outer layers and smooth inner layers. The surface textural properties are attributed to the defects induced by the sulfur intercalated into the lattice or bonded with the carbon. The XRD patterns and X-ray microanalysis studies show that iron serves as the seed for carbon nanohorn growth and iron sulfide is formed during synthesis.

N2 Gas Adsorption Sites of Single-Walled Carbon Nanotube Bundles: Identifying Interstitial Channels at Very Low Relative Pressure

Utilizing the nanoscale space created by carbon nanotubes (CNTs) is of importance for applications like energy storage devices, sensors, and functional materials. Gas adsorption is a versatile, quantitative characterization method to analyze nanoscale pore sizes and volumes. Here, we inspected N₂ adsorption to the nanospace formed by the bundles of single-walled CNTs with an average nanotube diameter of ca. 2.0 nm and its distributions of 0.7-4.1 nm. Based on comparisons among the as-grown, purified (opened), and heat-treated (closed) CNTs with similar geometric bundle structures, we found that the interstitial channels emerged from a very low relative pressure of approximately 10^-8 by removing the impurities from the CNT bundles, which is the first empirical demonstration. These findings can not only be utilized to understand the structures of CNT films, fibers, and bulks but also applied to porous materials science.

Ibandronate-Loaded Carbon Nanohorns Fabricated Using Calcium Phosphates as Mediators and Their Effects on Macrophages and Osteoclasts

Carbon nanohorns (CNHs), a type of nanocarbon, have been studied for the application of drug delivery systems (DDSs) because they are easily functionalized, support bone regeneration, can be used to perform photohyperthermia, have low toxicity, and are easily phagocytosed by macrophages. To take advantage of these features of CNHs, we developed a DDS for the local treatment of bone metastasis by loading the antibone resorption drug ibandronate (IBN) onto CNHs. The poor adsorption of IBN onto CNHs due to the weak hydrophilic-hydrophobic interaction was overcome by using calcium phosphates (CaPs) as mediators. In the fabrication process, we used oxidized CNH (OxCNH), which is less hydrophobic, onto which IBN was coprecipitated with CaP from a labile supersaturated CaP solution. OxCNH-CaP-IBN composite nanoparticles exerted stronger cell-suppressive effects than OxCNH and IBN in both murine macrophages (RAW264.7 cells) and osteoclasts (differentiated from RAW264.7 cells). OxCNH-CaP-IBN composite nanoparticles were efficiently phagocytosed by macrophage cells, where they specifically accumulated in lysosomes. The stronger cell-suppressive effects were likely due to intracellular delivery of IBN, i.e., the release of IBN from OxCNH-CaP-IBN composite nanoparticles via dissociation of CaP in the acidic environment of lysosomes. Our findings suggest that OxCNH-CaP-IBN composite nanoparticles are potentially useful for the local treatment of metastatic bone destruction.

Structure, synthesis, and sensing applications of single-walled carbon nanohorns

Single-walled carbon nanohorns (SWCNHs), a type of tapered carbon nanomaterials, are generally prepared by laser ablation method, arc method, and Joule heating method without the addition of metal catalysts, which makes them pure and environmentally friendly. The obtained aggregates of SWCNHs mainly have three different types of structure, dahlia-like, bud-like, and seed-like. Over the past few decades, they have been widely used in the fields of energy, medicine, chemistry, and sensing. The SWCNHs-based sensors have shown high sensitivity, rapid response, and excellent stability, which are mainly attributed to the excellent electrical conductivity, large electrochemical window, large specific surface area, and mechanical strength of SWCNHs. In this review, we systematically summarizes the structures, synthesis methods, and sensing applications of SWCNHs, including electrochemical sensors, photoelectrochemical sensors, electrochemiluminescence sensors, fluorescent sensors, and resistive sensors. Moreover, the development prospects of SWCNHs in this field are also discussed.

Carbon Nanohorn-Based Electrocatalysts for Energy Conversion

In the context of even more growing energy demands, the investigation of alternative environmentally friendly solutions, like fuel cells, is essential. Given their outstanding properties, carbon nanohorns (CNHs) have come forth as promising electrocatalysts within the nanocarbon family. Carbon nanohorns are conical nanostructures made of sp2 carbon sheets that form aggregated superstructures during their synthesis. They require no metal catalyst during their preparation and they are inexpensively produced in industrial quantities, affording a favorable candidate for electrocatalytic reactions. The aim of this article is to provide a comprehensive overview regarding CNHs in the field of electrocatalysis and especially, in oxygen reduction, methanol oxidation, and hydrogen evolution, as well as oxygen evolution from water splitting, underlining the progress made so far, and pointing out the areas where significant improvement can be achieved.

Mild oxidation-production of subnanometer-sized nanowindows of single wall carbon nanohorn

The size control of nanowindows on the graphene walls is indispensable to develop innovative adsorption and separation technologies. As single wall carbon nanohorn (SWCNH) consists of graphene wall, the permeation of ions through the nanowindows can be evaluated with adsorption measurement. We regulated the nanowindow size by use of mild oxidation at 473-523 K for 20-70 h. The explicit low pressure adsorption hysteresis was observed in the N₂ adsorption isotherms of thus-oxidized SWCNHs, suggesting the window size of 0.3-0.4 nm. Moreover, the aqueous phase adsorption measurement for Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺ indicates that the nanowindow size is smaller than about 0.37 nm, being close to the estimated size from N₂ adsorption.

Non-viral Gene Delivery

Although viral vectors comprise the majority of gene delivery vectors, their various safety, production, and other practical concerns have left a research gap to be addressed. The non-viral vector space encompasses a growing variety of physical and chemical methods capable of gene delivery into the nuclei of target cells. Major physical methods described in this chapter are microinjection, electroporation, and ballistic injection, magnetofection, sonoporation, optical transfection, and localized hyperthermia. Major chemical methods described in this chapter are lipofection, polyfection, gold complexation, and carbon-based methods. Combination approaches to improve transfection efficiency or reduce immunological response have shown great promise in expanding the scope of non-viral gene delivery.

Gas adsorption capacity in an all carbon nanomaterial composed of carbon nanohorns and vertically aligned carbon nanotubes

Whereas vertically aligned carbon nanotubes (VACNTs) typically show a promising adsorption behavior at high pressures, carbon nanohorns (CNHs) exhibit superior gas adsorption properties in the low pressure regime due to their inherent microporosity. These adsorption characteristics are further enhanced when both materials are opened at their tips. The so prepared composite material allows one to investigate the effect of physical entrapment of CO₂ molecules within the specific adsorption sites of VACNTs composed of opened double walled carbon nanotubes (CNTs) and in specific adsorption sites created by spherically aggregated opened single walled carbon nanohorns. Combining 50 wt% of tip opened CNTs with tip opened CNHs increases the CO₂ adsorption capacity of this material by ∼24% at 30 bar and 298 K compared to opened CNHs alone.

Structure, Properties, Functionalization, and Applications of Carbon Nanohorns

Carbon nanohorns (sometimes also known as nanocones) are conical carbon nanostructures constructed from an sp(2) carbon sheet. Nanohorns require no metal catalyst in their synthesis, and can be produced in industrial quantities. They provide a realistic and useful alternative to carbon nanotubes, and possibly graphene, in a wide range of applications. They also have their own unique behavior due to their specific conical morphology. However, their research and development has been slowed by several factors, notably during synthesis, they aggregate into spherical clusters ∼100 nm in diameter, blocking functionalization and treatment of individual nanocones. This limitation has recently been overcome with a new approach to separating these "dahlia-like" clusters into individual nanocones. In this review, we describe the structure, synthesis, and topology of carbon nanohorns, and provide a detailed review of nanohorn chemistry.

Nitrogen-induced surface area and conductivity modulation of carbon nanohorn and its function as an efficient metal-free oxygen reduction electrocatalyst for anion-exchange membrane fuel cells

Nitrogen-doped carbon morphologies have been proven to be better alternatives to Pt in polymer-electrolyte membrane (PEM) fuel cells. However, efficient modulation of the active sites by the simultaneous escalation of the porosity and nitrogen doping, without affecting the intrinsic electrical conductivity, still remains to be solved. Here, a simple strategy is reported to solve this issue by treating single-walled carbon nanohorn (SWCNH) with urea at 800 °C. The resulting nitrogen-doped carbon nanohorn shows a high surface area of 1836 m2 g(-1) along with an increased electron conductivity, which are the pre-requisites of an electrocatalyst. The nitrogen-doped nanohorn annealed at 800 °C (N-800) also shows a high oxygen reduction activity (ORR). Because of the high weight percentage of pyridinic nitrogen coordination in N-800, the present catalyst shows a clear 4-electron reduction pathway at only 50 mV overpotential and 16 mV negative shift in the half-wave potential for ORR compared to Pt/C along with a high fuel selectivity and electrochemical stability. More importantly, a membrane electrode assembly (MEA) based on N-800 provides a maximum power density of 30 mW cm(-2) under anion-exchange membrane fuel cell (AEMFC) testing conditions. Thus, with its remarkable set of physical and electrochemical properties, this material has the potential to perform as an efficient Pt-free electrode for AEMFCs.

Selective adsorption of bilirubin against albumin to oxidized single-wall carbon nanohorns

Bilirubin adsorption capacities of single-wall carbon nanohorns (SWNHs) are investigated to develop an efficient adsorbent in plasma apheresis. Pristine, thermally oxidized and H2O2-oxidized SWNHs are examined and it is demonstrated that higher oxidization levels of the SWNHs enhance bilirubin adsorption capacity owing to increase in their dispersibility and formation of nanoscaled holes on the SWNH walls. Under co-existance of albumin molecules, the bilirubin adsorption capacity of the SWNHs increases with the oxidation level whereas the albumin adsorption capacity is kept small. Bilirubin is selectively adsorbed to the SWNHs, especially to the SWNHs with high oxidation levels, against albumin. This selectivity is maintained under high-concentrations of albumin in the near-clinical environment.

Spatially controlled photothermal heating of bladder tissue through single-walled carbon nanohorns delivered with a fiberoptic microneedle device

Laser-based photothermal therapies for urothelial cell carcinoma (UCC) are limited to thermal ablation of superficial tumors, as treatment of invasive lesions is hampered by shallow light penetration in bladder tissue at commonly used therapeutic wavelengths. This study evaluates the utilization of sharp, silica, fiberoptic microneedle devices (FMDs) to deliver single-walled carbon nanohorns (SWNHs) serving as exogenous chromophores in conjunction with a 1,064-nm laser to amplify thermal treatment doses in a spatially controlled manner. Experiments were conducted to determine the lateral and depth dispersal of SWNHs in aqueous solution (0.05 mg/mL) infused through FMDs into the wall of healthy, inflated, ex vivo porcine bladders. SWNH-perfused bladder regions were irradiated with a free-space, CW, 1,064-nm laser in order to determine the SWNH efficacy as exogenous chromophores within the organ. SWNHs infused at a rate of 50 μL/min resulted in an average lateral expansion rate of 0.36 ± 0.08 cm(2)/min. Infused SWNHs dispersal depth was limited to the urothelium and muscular propria for 50 μL/min infusions of 10 min or less, but dispersed through the entire thickness after a 15-min infusion period. Irradiation of SWNH-perfused bladder tissue with 1,064 nm laser light at 0.95 W/cm(2) over 40 s exhibited a maximum increase of approximately 19 °C compared with an increase of approximately 3 °C in a non-perfused control. The results indicate that these silica FMDs can successfully penetrate into the bladder wall to rapidly distribute SWNHs with some degree of lateral and depth control and that SWNHs may be a viable exogenous chromophore for photothermal amplification of laser-based UCC treatments.

Single-walled carbon nanohorns as drug carriers: adsorption of prednisolone and anti-inflammatory effects on arthritis

Prednisolone (PSL), an anti-inflammatory glucocorticoid drug, was adsorbed on oxidized single-walled carbon nanohorns (oxSWNHs) in ethanol-water solvent. The quantity of adsorbed PSL on the oxSWNHs was 0.35-0.54 g/g depending on the sizes and numbers of holes on the oxSWNHs. PSL was adsorbed on both the outside and the inside of the oxSWNHs, and released quickly in a couple of hours and slowly within about one day from the respective places. The released quantity in culture medium strongly depended on the concentration of the PSL-oxSWNH complexes, suggesting that PSL adsorbing on oxSWNHs and PSL in the culture medium were in concentration equilibrium. The local injection of PSL-oxSWNHs into the tarsal joint of rats with collagen-induced arthritis (CIA) slightly retarded the progression of the arthritis compared with controls. By histological analysis of the ankle joint, the anti-inflammatory effect of PSL-oxSWNHs was also observed.

Manufacturing and physico-mechanical characterization of carbon nanohorns/polyacrylonitrile nanocomposites

The use of carbon nanohorns (SWCNHs) as a modifying filler in a polyacrylonitrile (PAN) matrix is studied with the goal of elaborating nanocomposites. The study deals with assessment of the dispersity of SWCNHs in a PAN polymer suspension. The SWCNHs were introduced into the PAN-based suspension using different methods, including mechanical stirring, ultrasonification and the combination of ultrasonification with addition of a surfactant. Agglomeration and dispersion processes of SWCNH in the polymer suspensions were studied using DLS technique and turbidimetry. The resulting properties of nanocomposite foils after solidification in water ambient were verified in various tests. The mechanical tensile properties (tensile strength, modulus and strain to fracture) of the nanocomposites before and after the dispersion process were compared. The nanocomposites obtained under optimally prepared suspension perform the highest strain to fracture in tensile test. Electrical resistivity and thermal conductivity of nanocomposites samples after appropriate dispersion of SWCNHs in the PAN suspension were also determined. The presence of SWCNH in the PAN suspension affects the structure of nanocomposites after solidification through changing structural ordering of the polymer. The study revealed that the polymeric suspensions prepared in optimum processing conditions contain the carbon aggregates the size of which correspond almost to the mean size of a dahlia flower-like structured particle, i.e., 50-250 nm and it was not possible to separate such particles into a single form of carbon nanohorn by the techniques used.

Carbon nanohorns accelerate bone regeneration in rat calvarial bone defect

A recent study showed that carbon nanohorns (CNHs) have biocompatibility and possible medical uses such as in drug delivery systems. It was reported that some kinds of carbon nanomaterials such as carbon nanotubes were useful for bone formation. However, the effect of CNHs on bone tissue has not been clarified. The purpose of this study was to evaluate the effect of CNHs on bone regeneration and their possible application for guided bone regeneration (GBR). CNHs dispersed in ethanol were fixed on a porous polytetrafluoroethylene membrane by vacuum filtration. Cranial defects were created in rats and covered by a membrane with/without CNHs. At two weeks, bone formation under the membrane with CNHs had progressed more than under that without CNHs and numerous macrophages were observed attached to CNHs. At eight weeks, there was no significant difference in the amount of newly formed bone between the groups and the appearance of macrophages was decreased compared with that at two weeks. Newly formed bone attached to some CNHs directly. These results suggest that macrophages induced by CNHs are related to bone regeneration. In conclusion, the present study indicates that CNHs are compatible with bone tissue and effective as a material for GBR.

Single-walled carbon nanohorns and their applications

Single-walled carbon nanohorns (SWCNHs) are horn-shaped single-walled tubules with a conical tip. They are generally synthesized by laser ablation of pure graphite without using metal catalyst with high production rate and high yield, and typically form radial aggregates. SWCNHs are essentially metal-free and very pure, which avoids cumbersome purification and makes them user-friendly and environmentally benign. Currently, SWCNHs have been widely studied for various applications, such as gas storage, adsorption, catalyst support, drug delivery system, magnetic resonance analysis, electrochemistry, biosensing application, photovoltaics and photoelectrochemical cells, photodynamic therapy, fuel cells, and so on. This review outlines the research progress on SWCNHs, including their properties, functionalization, applications, and outlook.

Prevention of carbon nanohorn agglomeration using a conjugate composed of comb-shaped polyethylene glycol and a peptide aptamer

Assured dispersibility is a prerequisite for clinical application of nanomaterials. Carbon nanomaterials have hydrophobic surfaces and thus readily agglomerate under aqueous conditions. Various conjugates composed of a carbon surface-binding moiety and polyethylene glycol (PEG) have been examined as dispersants for carbon nanomaterials. Here we synthesized a conjugate composed of a comb-shaped PEG (cPEG) and carbon nanomaterial-binding peptide (NHBP-1). The resultant cPEG-NHBP3 conjugate displayed multiple units (2.4 on average) of NHBP-1 on a single cPEG molecule whose average molecular weight was 15-20 kDa. cPEG-NHBP3 endowed single-walled carbon nanohorns (SWNHs) with good dispersibility in vitro, which could not be achieved with 20PEG-NHBP, a conjugate composed of linear 20 kDa PEG and a single NHBP-1 peptide. Notably, cPEG-NHBP1, which was similar to 20PEG-NHBP but had a comb-shaped PEG backbone, functioned better as a dispersant than 20PEG-NHBP, suggesting a graft-type PEG formula is better-suited for dispersing nanomaterials. Finally, cPEG-NHBP3 treatment substantially suppressed formation of SWNH agglomerates in mouse lung, suggesting the potential utility of SWNHs as a carrier in drug delivery systems.

Crucial functionalizations of carbon nanotubes for improved drug delivery: a valuable option?

Amidst the myriad of drug delivery systems able to enhance delivery, absorption and intracellular uptake of a bioactive molecule while protecting it from deactivation, Carbon Nanotubes (CNTs) have emerged as a recent and promising option especially in cancer therapy. This is mainly due to their unique properties, which render them extremely versatile through the incorporation of several functional groups and targeting molecules at the same time, while their natural shape allows them to selectively penetrate across biological barriers in a non-invasive way. In this expert review we aim to evaluate whether this innovative material, once chemically-modified with suitable functionalizations, can be considered as a valuable system in comparison to the already existing nanodevices. This will include the estimation of the most recent advances in the field of nanotechnology, together with a cautious evaluation of potential risks and hazards associated with the extensive use of this fascinating, but still unknown, nanomaterial.

Adsorption of polar and non-polar fluids in carbon nanotube bundles: computer simulation and experimental studies

The effects of adsorbate on the adsorption in a bundle of carbon nanotubes are investigated to explore the preferential adsorption over various adsorption sites: inside the tube, in the cusp interstices and in the square interstices outside the tubes. This is carried out with the Grand Canonical Monte Carlo simulation and the simulation results are tested against the experimental results of bundles of single wall carbon nanotubes (SWCN). With regard to adsorbate, we choose argon and nitrogen to represent simple fluids and water to represent strong associating fluids with strong orientation interaction. The preferential adsorption of argon and nitrogen depends on the tube size. For tube size smaller than 10.8 A, adsorption inside the tube is preferred because the solid-fluid potential is greatest in the tube interiors. While for larger tubes adsorption occurs initially in the small cusp interstices between the tubes, and as adsorption is progressed adsorption occurs inside the tube as well as the larger square interstices. At higher pressures capillary condensation occurs in the square interstices. For water, however, the adsorption mechanism is different. Its adsorption occurs dominantly inside the tube, irrespective of the tube size. This is due to the requirement of appropriate geometry to allow hydrogen bonding among water molecules to occur. The small cusp interstices do not provide proper space for clusters of hydrogen bonded waters, while the larger square interstices are too large and hence the solid-fluid potential is not strong enough to induce adsorption unless the partial pressure is sufficiently high. Finally the model of these fluids and carbon nanotube is tested with the experimental data of a commercial SWCN, and the simulation results are in agreement with the data.

Functionalization of carbon nanomaterials by evolutionary molecular engineering: Potential application in drug delivery systems

By virtue of the progress made in evolutionary molecular engineering, peptide aptamers that specifically recognize target molecules are now routinely created using a peptide phage display system. The system was originally developed for isolating peptides that specifically recognized biomacromolecules (e.g. proteinous receptors), but are now also being used to acquire peptide motifs that bind to inorganic materials, such as semiconductors, metals and carbon nanomaterials. We have created the peptide aptamer against carbon nanohorns, a vesicular carbon nanomaterial whose size is 80-100 nm in diameter. By combining the peptide motif that has affinity to the surfaces of carbon nanohorns with peptide aptamers that can target specific organs, we can functionalize the carbon nanomaterial to provide novel types of carriers for drug delivery systems.

Fabrication of ZnPc/protein nanohorns for double photodynamic and hyperthermic cancer phototherapy

Multifunctionalization of carbon nanotubules is easily achieved by attaching functional molecules that provide specific advantages for microscopic applications. We fabricated a double photodynamic therapy (PDT) and photohyperthermia (PHT) cancer phototherapy system that uses a single laser. Zinc phthalocyanine (ZnPc) was loaded onto single-wall carbon nanohorns with holes opened (SWNHox), and the protein bovine serum albumin (BSA) was attached to the carboxyl groups of SWNHox. In this system, ZnPc was the PDT agent, SWNHox was the PHT agent, and BSA enhanced biocompatibility. The double phototherapy effect was confirmed in vitro and in vivo. When ZnPc-SWNHox-BSA was injected into tumors that were subcutaneously transplanted into mice, the tumors almost disappeared upon 670-nm laser irradiation. In contrast, the tumors continued to grow when only ZnPc or SWNHox-BSA was injected. We conclude that carbon nanotubules may be a valuable new tool for use in cancer phototherapy.

Water-dispersed single-wall carbon nanohorns as drug carriers for local cancer chemotherapy

Aim: Functional analyses of water-dispersed carbon nanohorns with antitumor activity were performed to explore their potential as a drug carrier for local cancer chemotherapy. Materials & methods: Water-dispersed carbon nanohorns were prepared through adsorption of polyethylene glycol-doxorubicin conjugate (PEG–DXR) onto oxidized single-wall carbon nanohorns (oxSWNHs). PEG–DXR-bound oxSWNHs were administered intratumorally to human nonsmall cell lung cancer-cell NCI-H460-bearing mice. Results & discussion: When injected intratumorally, PEG–DXR-bound oxSWNHs caused significant retardation of tumor growth associated with prolonged DXR retention in the tumor. In accordance with this DXR retention, a large number of oxSWNH agglomerates was found in the periphery of the tumor. Histological analyses showed migration of oxSWNHs to the axillary lymph node, which is a major site of breast cancer metastasis near the tumor, possibly by means of interstitial lymphatic-fluid transport. Conclusions: These results suggest that water-dispersed oxSWNHs may thus be useful as a drug carrier for local chemotherapy.

The interaction of nitrogen molecules with (4, 0) single-walled carbon nanotube: electronic and structural effects

The electronic structure and energetics of (4, 0) single-walled carbon nanotubes (CNTs) interacting with nitrogen have been studied using density-functional calculations. We show that the nanotubes become covered with a stable sheath of N(2) molecules. We have constructed potential energy curves which can be used for the thermodynamic analysis of N(2) adsorption and desorption processes. Our results show that any analysis of the observed properties (for example thermodynamics, stability, and photoluminescence) of air-exposed CNTs needs to consider the N(2) adsorbed on the CNTs.

Distribution of carbon nanotube sizes from adsorption measurements and computer simulation

The method for the evaluation of the distribution of carbon nanotube sizes from the static adsorption measurements and computer simulation of nitrogen at 77 K is developed. We obtain the condensation/evaporation pressure as a function of pore size of a cylindrical carbon tube using Gauge Cell Monte Carlo Simulation (Gauge Cell MC). To obtain the analytical form of the relationships mentioned above we use Derjaguin-Broekhoff-deBoer theory. Finally, the pore size distribution (PSD) of the single-walled carbon nanohorns (SWNHs) is determined from a single nitrogen adsorption isotherm measured at 77 K. We neglect the conical part of an isolated SWNH tube and assume a structureless wall of a carbon nanotube. We find that the distribution of SWNH sizes is broad (internal pore radii varied in the range 1.0-3.6 nm with the maximum at 1.3 nm). Our method can be used for the determination of the pore size distribution of the other tubular carbon materials, like, for example, multiwalled or double-walled carbon nanotubes. Besides the applicable aspect of the current work the deep insight into the problem of capillary condensation/evaporation in confined carbon cylindrical geometry is presented. As a result, the critical pore radius in structureless single-walled carbon tubes is determined as being equal to three nitrogen collision diameters. Below that size the adsorption-desorption isotherm is reversible (i.e., supercritical in nature). We show that the classical static adsorption measurements combined with the proper modeling of the capillary condensation/evaporation phenomena is a powerful method that can be applied for the determination of the distribution of nanotube sizes.

Effect of functional groups at hole edges on cisplatin release from inside single-wall carbon nanohorns

We incorporated cisplatin inside single-wall carbon nanohorns (NHs) and revealed that 70% of the cisplatin was released from NHs having holes with hydrogen-terminated edges when they were immersed in phosphate-buffered saline (PBS). However, only 15% was released from NHs having holes with oxygen-containing functional groups at the hole edges (NHox). Elemental analysis indicated that -COOH and -OH groups at the hole edges of NHox changed mainly to -COONa and -ONa groups by immersion in PBS. These groups decreased the practical hole diameters, which resulted in hindering the cisplatin release from NHox. This means that the release of the material from inside NHox would be controlled by chemically modifying the functional groups attached to the hole edges of NHox; thus the potential applicability of NHox to a material carrier would be enhanced.

Synthesis of ultrafine Gd2O3 nanoparticles inside single-wall carbon nanohorns

The large diameter of single-wall carbon nanohorns (SWNHs) allows various molecules to be easily incorporated in hollow nanospaces. In this report, we prove that the nanospaces of SWNHs even work as the chemical reaction field at high temperature; that is, Gd-acetate clusters inside SWNHs were transformed into ultrafine Gd(2)O(3) nanoparticles with their particle size retained even after heat-treatment at 700 degrees C. This indicates that the confinement of the Gd-acetate clusters in a deep potential well of the SWNH nanospaces prevented a migration to form larger particles, giving rise to ultrafine Gd(2)O(3) nanoparticles of 2.3 nm in average diameter, which is much smaller than the case without SWNHs. The Gd(2)O(3) nanoparticles thus obtained were demonstrated to be actually useful to the magnetic resonance imaging. We believe that the presented effectiveness of the inner hollow spaces of SWNHs, therefore, also those of the carbon nanotubes, for high-temperature chemical reactions should be highlighted, and that the thus produced novel nanomaterials are promising to expand the fields of nanoscience.

Conversion of a monodispersed globular protein into an amyloid-like filament by appending an artificial peptide at the N-terminal

The soluble, globular, alpha-helix-rich peptide SipA(446-684) is a domain of a bacterial protein that binds to mammalian filamentous-actin and re-arranges the host cell's cytoskeleton. We show that adding two copies of NHBP-1, a carbon nanomaterial binding peptide, to its N-terminal can induce SipA(446-684) to polymerize and assume a fibrillar structure under physiological conditions. The fibrils formed showed thioflavine T and Congo red staining profiles that are characteristic of and specific for amyloid-like structures. The alpha-helical structure of the globular protein was retained in the fibrils, suggesting the appended NHBP-1 sequence plays a key role in the formation of cross-beta spines within the fibrils. Consistent with that idea, we observed that a synthetic NHBP-1 peptide can form an amyloid-like structure under appropriate conditions. Thus, our findings add a new subtype of amyloid-like structure formation and suggest this method of assembly could be exploited in nano-biotechnology.

Preparing a Magnetically Responsive Single-Wall Carbon Nanohorn Colloid by Anchoring Magnetite Nanoparticles

A single-wall carbon nanohorn (SWNH) colloid was made to be magnetically responsive by anchoring magnetite nanoparticles prepared by the homogeneous mixing of FeCl(2)-FeCl(3) and NaOH solutions. Transmission electron microscopy observation showed the high dispersion of magnetite particles of 2-9 nm on the surface of the SWNH colloid, coinciding with the broad X-ray diffraction peaks of the magnetites. The magnetization measurements showed that the magnetite nanoparticles-anchored SWNH (mag-SWNH) colloid has the hybrid property of ferrimagnetism and superparamagnetism. It was demonstrated that mag-SWNH colloid dispersed in water by sonication responded to an external magnetic field, gathering toward a magnet. N(2) adsorption experiments showed the high nanoporosity of mag-SWNHs and that magnetite nanoparticles were preferably anchored at "nanowindow" sites and the entrance sites of interstitial pores. This magnetically responsive SWNH colloid should contribute to the field of drug delivery.

Controlling the Incorporation and Release of C60 in Nanometer-Scale Hollow Spaces inside Single-Wall Carbon Nanohorns

We succeeded in large-scale preparation of single-wall carbon nanohorns (SWNH) encapsulating C60 molecules in a liquid phase at room temperature using a "nano-precipitation" method, that is, complete evaporation of the toluene from a C60-SWNH-toluene mixture. The C60 molecules were found to occupy 6-36% of the hollow space inside the SWNH, depending on the initial quantity of C60. We showed that the C60 in C60@SWNHox was quickly released in toluene, and the release rate decreased by adding ethanol to toluene. Numerical analysis of the release profiles indicated that there were fast and slow release processes. We consider that the incorporation quantity and the release rate of C60 were controllable in/from SWNHs because SWNHs have large diameters, 2-5 nm.

Opening Mechanism of Internal Nanoporosity of Single-Wall Carbon Nanohorn

Single-wall carbon nanohorn (SWNH), which is a tubular particle with a cone cap, was oxidized in an oxygen flow at various temperatures. N(2) adsorption at 77 K, thermogravimetry (TG), differential thermal analysis (DTA), transmission electron microscopy, and Raman spectroscopy measurements were carried out on the oxidized SWNHs. The specific surface area of the oxidized SWNHs can be controlled by oxidation temperature, giving the maximum value of 1420 m(2)/g. The pore size distribution by the BJH method and the comparison plot of the N(2) adsorption isotherms of SWNH oxidized at different temperatures against that of as-grown SWNH revealed the minimum oxidation temperature for opening internal nanopores. TG-DTA analyses determined the components of as-grown SWNH: amorphous carbon 2.5 wt %, defective carbon at the cone part 15 wt %, tubular carbon 70 wt %, and graphitic carbon 12 wt %. These systematic analyses provided the exact internal nanopore volume of 0.49 mL/g for pure SWNH particles.

Quantum Effects on Hydrogen Isotope Adsorption on Single-Wall Carbon Nanohorns

H(2) and D(2) adsorption on single-wall carbon nanohorns (SWNHs) have been measured at 77 K, and the experimental data were compared with grand canonical Monte Carlo simulations for adsorption of these hydrogen isotopes on a model SWNH. Quantum effects were included in the simulations through the Feynman-Hibbs effective potential. The simulation predictions show good agreement with the experimental results and suggest that the hydrogen isotope adsorption at 77 K can be successfully explained with the use of the effective potential. According to the simulations, the hydrogen isotopes are preferentially adsorbed in the cone part of the SWNH with a strong potential field, and quantum effects cause the density of adsorbed H(2) inside the SWNH to be 8-26% smaller than that of D(2). The difference between H(2) and D(2) adsorption increases as pressure decreases because the quantum spreading of H(2), which is wider than that of D(2), is fairly effective at the narrow conical part of the SWNH model. These facts indicate that quantum effects on hydrogen adsorption depend on pore structures and are very important even at 77 K.

Studies on the Adsorption of Organic Materials Inside Thick Carbon Nanotubes

We clarified the adsorption sites inside the single-wall carbon nanohorns (SWNHs), a type of single-wall carbon nanotubes having thick diameters of 2-5 nm, through the thermogravimetric analysis of the desorption of xylene and benzene from SWNHs. The influence of the sizes of holes piercing through the SWNH walls was also examined. Three types of adsorption sites were found inside the SWNH tubes, which were assigned to the tube tips, the sidewalls, and central regions of the hollow spaces. The experimental results also suggested that the adsorbed xylene and benzene were stabilized mainly by weak self-interactions at the central regions and their quick desorption was caused by the weak self-interactions.

Quasi One-Dimensional Nanopores in Single-Wall Carbon Nanohorn Colloids Using Grand Canonical Monte Carlo Simulation Aided Adsorption Technique

The average interstitial nanopore structure of single-wall carbon nanohorn (SWNH) assemblies was determined using X-ray diffraction and grand canonical Monte Carlo (GCMC) simulation aided N(2) adsorption at 77 K. The interstitial nanopores of SWNH assemblies can be regarded as quasi one-dimensional pores due to the partial orientation of the SWNH particles; the average pore width of the interstitial pores is 0.6 nm. Good agreement between the GCMC simulation of a structural model with one-dimensional interstitial nanopores and an experimental adsorption isotherm below P/P(0) = 10(-4) is evidence of the quasi one-dimensionality of the interstitial nanopores. A snapshot from the GCMC simulation showed one-dimensional growth of adsorbed N(2) molecules.

Palladium Nanoclusters Deposited on Single-Walled Carbon Nanohorns

This study reports a direct route for deposition of Pd nanoclusters on single-walled carbon nanohorns (SWNHs) in a one step reaction involving chemical reduction of metal ions in the presence of a polymer-stabilizer. The applied strategy provides small Pd nanoclusters with an average diameter of approximately 2.3 nm robustly attached to the nanotubular carbon. The attachment is mediated by the polymer (poly(vinylpyrrolidone), PVP) used to stabilize the nanoclusters.