Atomic-resolution STEM-EDS studies of cation ordering in Ti-Nb oxide crystals.

Ternary metal oxide compounds, such as Ti-Nb and Nb-W oxides, have renewed research interest in energy storage materials because these oxides contain multivalent metal ions that may be able to control the ion transport in solid lithium batteries. One of these oxides is Ti2Nb10O29, which is composed of metal-oxygen octahedra connected through corner-sharing and edge-sharing to form "block structures". In the early 1970s Von Dreele and Cheetham proposed a metal-atoms ordering in this oxide crystal using Rietveld refined neutron powder diffraction method. Most recent studies on these oxides, however, have not considered cation ordering in evaluating the battery electrode materials. In this paper, by utilizing the latest scanning transmission electron microscopy combined with energy dispersive X-ray spectroscopy imaging technology, the cation chemical ordering in those oxide crystals was directly revealed at atomic resolution.

Carbon nanohorn coating by electrodeposition accelerate bone formation on titanium implant.

Direct contact between bone and implant materials is required for dental implants. Titanium is used for the implant material owing to its mechanical and biological properties. The anodisation as the surface treatment was employed to enhance osteogenesis around titanium. Moreover, carbon nanohorn (CNH), a type of nanometer-sized carbon material, was reported to promote the bone formation. Thus, it is expected that if the surface of anodised Ti (AnTi) is modified with CNHs, Ti-bone contact would be enhanced. In this study, the Ti surface was modified with CNHs by electrophoresis and obtained anodised titanium coated with CNHs (CNH/AnTi). In vitro, CNH/AnTi attracted osteoblastic cells more than AnTi, thereby the proliferation of osteoblastic cell was enhanced by CNH/AnTi more than by AnTi. In vivo, at 7 and 28 days after implantation of CNH/AnTi or AnTi into the rat femur, more aggressive bone formation was observed on the surface of CNH/AnTi than on AnTi. More importantly, the area where newly formed bone tissue directly attached to CNH/AnTi was significantly larger than that for AnTi, suggesting that "contact osteogenesis" was accelerated on CNH/AnTi during the early post-implantation period. CNH/AnTi would be advantageous especially for the early stages of bone regeneration after surgery.

Time-dependent degradation of carbon nanotubes correlates with decreased reactive oxygen species generation in macrophages.

Introduction and objective: With the increase in carbon nanotube-based products on the commercial market, public concern regarding the possible toxicity of these nanomaterials has attracted much attention. Although previous studies found no obvious toxicity related to carbon nanotubes (CNTs), their safety has not been established because long-term evaluation is still needed. In vitro assays are used to understand the toxicity of nanomaterials. However, the data published so far were generated in short-term assays in which cells are continuously exposed to CNTs. Therefore, the objective of this study is to quantitatively assess the relative long-term cytotoxicity and degradation of CNTs after uptake by macrophages. Methods: We used macrophage cell line of RAW 264.7 and primary rat Kupffer cells to investigate macrophage uptake of CNTs as well as their quantity changes up to a relatively late time point after uptake (7 days) by measuring optical absorbance in the near infrared region and Raman spectra of CNTs in the cell lysates. The time-dependent cytotoxicity was evaluated by measuring reactive oxygen species (ROS), glutathione, cell viability, and caspase 3/7 activity in 1-7 days. Results: CNTs were degraded by approximately 25-30% within first 4 days after uptake; however, and no additional degradation occurred for the remainder of the 7-day test period. Generation of ROS by macrophages decreased as CNT degradation occurred, returning to control levels by Day 7. In the meantime, the glutathione level gradually recovered over time. There were no changes in cell viability or caspase 3/7 activation during CNT degradation. Conclusion: These results confirm that degradation of CNTs by macrophages is associated with ROS generation. The data also suggest that CNT cytotoxicity decreases as they are degraded.

A Simple Method for Removal of Carbon Nanotubes from Wastewater Using Hypochlorite.

Carbon nanotubes (CNTs) have been applied in a wide range of fields, such as materials, electronics, energy storages, and biomedicine. With the rapid increase in CNTs industrialization, more and more CNT-containing wastewater is being produced. Since concerns about the toxic effects of CNTs on human health persist, CNT-containing wastewater should not be released into the environment without purification, but no effective methods have been reported. In the present study, we report a simple method to eliminate CNTs from industrial or laboratorial wastewater using sodium hypochlorite. Direct treatment of aqueous dispersions with sodium hypochlorite solution completely degraded CNTs into carbon oxides or carbonates ions. Since hypochlorite is environmentally friendly and frequently used as a disinfectant or bleaching agent in domestic cleaning, this method is practical for purification of CNT-contaminated industrial wastewater.

Immobilization of a carbon nanomaterial-based localized drug-release system using a bispecific material-binding peptide.

INTRODUCTION: Inorganic materials are widely used in medical devices, such as artificial hearts, vessels, and joints, in stents, and as nanocarriers for drug-delivery systems. Carbon nanomaterials are of particular interest due to their biological inertness and their capability to accommodate molecules. Several attempts have been proposed, in which carbon nanomaterials are used as nanocarriers for the systemic delivery of drugs. MATERIALS AND METHODS: We developed a drug-delivery system in which oxidized single-walled carbon nanohorns (oxSWNHs) were immobilized on a titanium (Ti) surface using material-binding peptides to enable localized drug delivery. For this purpose, we utilized a bispecific peptidic aptamer comprising a core sequence of a Ti-binding peptide and a SWNH-binding peptide to immobilize oxSWNHs on Ti. RESULTS: Scanning electron microscopy was used to confirm the presence of oxSWNHs adsorbed onto the Ti surface, and a quartz crystal microbalance was used to evaluate the binding process during oxSWNH adsorption. The oxSWNHs-ornamented Ti substrate was nontoxic to cells and released biologically active dexamethasone over a sustained period. CONCLUSION: This oxSWNHs-immobilized system can be used to modify the surface of Ti in implants and be loaded with drugs that stimulate osteogenesis and bone regeneration.

One-dimensional nanowires of pseudoboehmite (aluminum oxyhydroxide γ-AlOOH).

We report the discovery of a 1D crystalline structure of aluminum oxyhydroxide. It was found in a commercial product of fibrous pseudoboehmite (PB), γ-AlOOH, synthesized easily with low cost. The thinnest fiber found was a ribbon-like structure of only two layers of an Al-O octahedral double sheet having a submicrometer length along its c axis and 0.68-nm thickness along its b axis. This thickness is only slightly larger than half of the lattice parameter of the b-axis unit cell of the boehmite crystal (b/2 = 0.61 nm). Moreover, interlayer splittings having an average width of 1 nm inside the fibrous PB are found. These wider interlayer spaces may have intercalation of water, which is suggested by density functional theory (DFT) calculation. The fibers appear to grow as almost isolated individual filaments in aqueous Al-hydroxide sols and the growth direction of fibrous PB is always along its c axis.

Radiolabeling, whole-body single photon emission computed tomography/computed tomography imaging, and pharmacokinetics of carbon nanohorns in mice.

In this work, we report that the biodistribution and excretion of carbon nanohorns (CNHs) in mice are dependent on their size and functionalization. Small-sized CNHs (30-50 nm; S-CNHs) and large-sized CNHs (80-100 nm; L-CNHs) were chemically functionalized and radiolabeled with [(111)In]-diethylenetriaminepentaacetic acid and intravenously injected into mice. Their tissue distribution profiles at different time points were determined by single photon emission computed tomography/computed tomography. The results showed that the S-CNHs circulated longer in blood, while the L-CNHs accumulated faster in major organs like the liver and spleen. Small amounts of S-CNHs- and L-CNHs were excreted in urine within the first few hours postinjection, followed by excretion of smaller quantities within the next 48 hours in both urine and feces. The kinetics of excretion for S-CNHs were more rapid than for L-CNHs. Both S-CNH and L-CNH material accumulated mainly in the liver and spleen; however, S-CNH accumulation in the spleen was more prominent than in the liver.

Carbon nanohorns allow acceleration of osteoblast differentiation via macrophage activation.

Carbon nanohorns (CNHs), formed by a rolled graphene structure and terminating in a cone, are promising nanomaterials for the development of a variety of biological applications. Here we demonstrate that alkaline phosphatase activity is dramatically increased by coculture of human monocyte derived macrophages (hMDMs) and human mesenchymal stem cells (hMSCs) in the presence of CNHs. CNHs were mainly localized in the lysosome of macrophages more than in hMSCs during coculturing. At the same time, the amount of Oncostatin M (OSM) in the supernatant was also increased during incubation with CNHs. Oncostatin M (OSM) from activated macrophage has been reported to induce osteoblast differentiation and matrix mineralization through STAT3. These results suggest that the macrophages engulfed CNHs and accelerated the differentiation of mesenchymal stem cells into the osteoblast via OSM release. We expect that the proof-of-concept on the osteoblast differentiation capacity by CNHs will allow future studies focused on CNHs as ideal therapeutic materials for bone regeneration.

Ultrafast electron transfer in all-carbon-based SWCNT-C60 donor-acceptor nanoensembles connected by poly(phenylene-ethynylene) spacers.

Building all-carbon based functional materials for light energy harvesting applications could be a solution to tackle and reduce environmental carbon output. However, development of such all-carbon based donor-acceptor hybrids and demonstration of photoinduced charge separation in such nanohybrids is a challenge since in these hybrids part of the carbon material should act as an electron donating or accepting photosensitizer while the second part should fulfil the role of an electron acceptor or donor. In the present work, we have successfully addressed this issue by synthesizing covalently linked all-carbon-based donor-acceptor nanoensembles using single-walled carbon nanotubes (SWCNTs) as the donor and C60 as the acceptor. The donor-acceptor entities in the nanoensembles were connected by phenylene-ethynylene spacer units to achieve better electronic communication and to vary the distance between the components. These novel SWCNT-C60 nanoensembles have been characterized by a number of techniques, including TGA, FT-IR, Raman, AFM, absorbance and electrochemical methods. The moderate number of fullerene addends present on the side-walls of the nanotubes largely preserved the electronic structure of the nanotubes. The thermodynamic feasibility of charge separation in these nanoensembles was established using spectral and electrochemical data. Finally, occurrence of ultrafast electron transfer from the excited nanotubes in these donor-acceptor nanohybrids has been established by femtosecond transient absorption studies, signifying their utility in building light energy harvesting devices.

Ethane adsorption on aggregates of dahlia-like nanohorns: experiments and computer simulations.

This is a report on a study of the adsorption characteristics of ethane on aggregates of unopened dahlia-like carbon nanohorns. This sorbent presents two main groups of adsorption sites: the outside surface of individual nanohorns and deep, interstitial spaces between neighbouring nanohorns towards the interior of the aggregates. We have explored the equilibrium properties of the adsorbed ethane films by determining the adsorption isotherms and isosteric heat of adsorption. Computer simulations performed on different model structures indicate that the majority of ethane adsorption occurs on the outer region of the aggregates, near the ends of the nanohorns. We have also measured the kinetics of adsorption of ethane on this sorbent. The measurements and simulations were conducted along several isotherms spanning the range between 120 K and 220 K.

Sorption Kinetics on Open Carbon Nanohorn Aggregates: The Effect of Molecular Diameter.

We present the results of a study of the kinetics of adsorption on aggregates of open carbon nanohorns using argon and CF4 sorbates. We measured the equilibration times for each value of the sorbent loading along eight adsorption isotherms (four isotherms for each sorbate species). We found that: the equilibration times decrease as the sorbent loading (and the equilibrium pressure of the coexisting gas) increases, for a given temperature; and, that, for a given value of the sorbent loading, the equilibration times decrease with increasing temperature. When considering the effect of scaling of the temperatures by the respective critical temperatures we found that, at the same scaled temperature and at comparable loadings, the equilibration times for CF4 were longer than those for argon. We discuss a possible explanation for this result.

Room-temperature Y-type emission of perylenes by encapsulation within single-walled carbon nanotubes.

Fluorescent materials that exhibit large Stokes shifts are useful for suppressing aggregation-caused quenching. Controlling the self-trapped exciton (STE) states in organic dyes with a dimeric structure is one way of tuning Stokes shifts. However, this leads to the spectral broadening of the emissions at room temperature owing to the effects of the surrounding materials on the excited dimers. Here, we demonstrate the effects of confining organic dyes on their optical properties via the encapsulation of perylene molecules within single-walled carbon nanotubes. The encapsulated dimeric perylene exhibits fluorescence with large Stokes shifts and long lifetimes through the STE states. In particular, a noticeable emission of dimeric perylene is observed with a vibronic structure at room temperature; this resembles the Y-type emission of dimeric α-perylene crystals observed only at low temperatures. The results suggest that the isolation of the excited perylene dimers plays an important role in the occurrence of the room-temperature Y-emission.

Postsynthesis of h-BN/Graphene Heterostructures Inside a STEM.

Combinations of 2D materials with different physical properties can form heterostructures with modified electrical, mechanical, magnetic, and optical properties. The direct observation of a lateral heterostructure synthesis is reported by epitaxial in-plane graphene growth from the step-edge of hexagonal BN (h-BN) within a scanning transmission electron microscope chamber. Residual hydrocarbon in the chamber is the carbon source. The growth interface between h-BN and graphene is atomically identified as largely N-C bonds. This postgrowth method can form graphene nanoribbons connecting two h-BN domains with different twisting angles, as well as isolated carbon islands with arbitrary shapes embedded in the h-BN layer. The electronic properties of the vertically stacked h-BN/graphene heterostructures are investigated by electron energy-loss spectroscopy (EELS). Low-loss EELS analysis of the dielectric response suggests a robust coupling effect between the graphene and h-BN layers.

Synthesis, characterization and photoinduced charge separation of carbon nanohorn-oligothienylenevinylene hybrids.

The covalent coupling between oligo(thienylenevinylenes) (nTVs) and carbon nanohorns (CNHs) has been investigated. The resulting nanohybrids have been characterized by a combination of several techniques, including thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HR-TEM) and Raman spectroscopy. The photophysical properties of the new hybrids were investigated by steady-state and time-resolved spectroscopic techniques. A transient signal characterized by two kinetic regimes, one short decay within 0.5 µs corresponding to around 80% of the total signal and another much longer-lived decay of 10 µs, has been detected. The transient absorption spectra are characterized by a continuous absorption that increases in intensity towards shorter wavelengths, with a maximum at 430 nm. These transient signals have been assigned to the charge-separated state delocalized on CNHs based on the quenching behavior and by comparison with the photophysical properties of nTV in the absence and presence of quenchers. The photophysical behavior of covalent nTV-CNH conjugates with microsecond transients due to electrons and holes on CNHs contrasts with the absence of any transient for analogous nTV-C60 conjugates, for which charge separation was not observed at timescales longer than nanoseconds. The photochemical behavior of CNHs is believed to derive from the amphoteric (electron donor and acceptor) properties of CNHs and from the larger number of carbon atoms (efficient delocalization) in CNHs compared with C60.

Preparation of small-sized graphene oxide sheets and their biological applications.

By using carbon nanohorns as starting materials, small- and uniform-sized graphene oxide (S-GO) sheets can be prepared in high yields via an oxidation method. The obtained S-GO sheets have a band-like structure with a length of 20-50 nm, a width of 2-10 nm, and a thickness of 0.5-5 nm. S-GO sheets are hydrophilic due to abundant oxygenated groups on the surfaces and edges; hence, this nanomaterial is highly dispersive in aqueous solutions and some hydrophilic organic solvents. Additionally, like other S-GO samples, the S-GO sheets prepared here are strongly fluorescent over the visible light wavelength region. These characteristics underscore the high potential of S-GO sheets for nanomedical and diagnostic applications. In proof-of-concept experiments, the S-GO sheets were conjugated with an arginine-glycine-aspartic acid derivative for tumour-targeting drug delivery applications, and with an immunoglobulin G antibody for immunoassay applications.

Synthesis of single-walled carbon nanotubes on graphene layers.

Here, we report the synthesis of semiconducting single-walled carbon nanotubes with a narrow diameter distribution between 0.67 and 1.1 nm via chemical vapour deposition on graphene layers using Pt catalysts.

Not nanocarbon but dispersant induced abnormality in lysosome in macrophages in vivo.

The properties of nanocarbons change from hydrophobic to hydrophilic as a result of coating them with dispersants, typically phospholipid polyethylene glycols, for biological studies. It has been shown that the dispersants remain attached to the nanocarbons when they are injected in mice and influence the nanocarbons' biodistribution in vivo. We show in this report that the effects of dispersants also appear at the subcellular level in vivo. Carbon nanohorns (CNHs), a type of nanocarbon, were dispersed with ceramide polyethylene glycol (CPEG) and intravenously injected in mice. Histological observations and electron microscopy with energy dispersive x-ray analysis revealed that, in liver and spleen, the lysosome membranes were damaged, and the nanohorns formed a complex with hemosiderin in the lysosomes of the macrophages. It is inferred that the lysosomal membrane was damaged by sphigosine generated as a result of CPEG decomposition, which changed the intra lysosomal conditions, inducing the formation of the CPEG-CNH and hemosiderin complex. For comparison, when glucose was used instead of CPEG, neither the nanohorn­hemosiderin complex nor lysosomal membrane damage was found. Our results suggest that surface functionalization can control the behavior of nancarbons in cells in vivo and thereby improve their suitability for medical applications.

Biodegradation of carbon nanohorns in macrophage cells.

With the rapid developments in the medical applications of carbon nanomaterials such as carbon nanohorns (CNHs), carbon nanotubes, and graphene based nanomaterials, understanding the long-term fate, health impact, excretion, and degradation of these materials has become crucial. Herein, the in vitro biodegradation of CNHs was determined using a non-cellular enzymatic oxidation method and two types of macrophage cell lines. Approximately 60% of the CNHs was degraded within 24 h in a phosphate buffer solution containing myeloperoxidase. Furthermore, approximately 30% of the CNHs was degraded by both RAW 264.7 and THP-1 macrophage cells within 9 days. Inflammation markers such as pro-inflammatory cytokines interleukin 6 and tumor necrosis factor α were not induced by exposure to CNHs. However, reactive oxygen species were generated by the macrophage cells after uptake of CNHs, suggesting that these species were actively involved in the degradation of the nanomaterials rather than in an inflammatory pathway induction.

Photofunctional nanomodulators for bioexcitation.

A single organism comprises diverse types of cells. To acquire a detailed understanding of the biological functions of each cell, comprehensive control and analysis of homeostatic processes at the single-cell level are required. In this study, we develop a new type of light-driven nanomodulator comprising dye-functionalized carbon nanohorns (CNHs) that generate heat and reactive oxygen species under biologically transparent near-infrared (NIR) laser irradiation. By exploiting the physicochemical properties of the nanohorns, cellular calcium ion flux and membrane currents were successfully controlled at the single-cell level. In addition, the nanomodulator allows a remote bioexcitation of tissues during NIR laser exposure making this system a powerful tool for single-cell analyses and innovative cell therapies.