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.

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.

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.

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.

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.

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.

Photothermic regulation of gene expression triggered by laser-induced carbon nanohorns.

The development of optical methods to control cellular functions is important for various biological applications. In particular, heat shock promoter-mediated gene expression systems by laser light are attractive targets for controlling cellular functions. However, previous approaches have considerable technical limitations related to their use of UV, short-wavelength visible (vis), and infrared (IR) laser light, which have poor penetration into biological tissue. Biological tissue is relatively transparent to light inside the diagnostic window at wavelengths of 650-1,100 nm. Here we present a unique optical biotechnological method using carbon nanohorn (CNH) that transforms energy from diagnostic window laser light to heat to control the expression of various genes. We report that with this method, laser irradiation within the diagnostic window resulted in effective heat generation and thus caused heat shock promoter-mediated gene expression. This study provides an important step forward in the development of light-manipulated gene expression technologies.

Carbon nanohorns as a scaffold for the construction of disposable electrochemical immunosensing platforms. Application to the determination of fibrinogen in human plasma and urine.

We describe in this work a novel electrochemical immunosensor design making use of carbon nanohorns (CNHs) as a scaffold for the preparation of disposable immunosensing platforms for the determination of fibrinogen (Fib). The approach involved the immobilization of Fib onto activated CNHs deposited on screen-printed carbon electrodes (SPCEs) and the implementation of an indirect competitive assay using anti-Fib labeled with horseradish peroxidase (HRP) and hydroquinone (HQ) as the redox mediator. Both CNHs and the Fib-CNHs covalent assembly were characterized by microscopic and electrochemical techniques. The different variables affecting the analytical performance of the amperometric immunosensing strategy were optimized. The calibration plot for Fib allowed a range of linearity between 0.1 and 100 µg/mL (r(2) = 0.994) and a detection limit of 58 ng/mL to be achieved. The Fib-CNHs/SPCEs exhibited an excellent storage stability of at least 42 days. The developed immunosensor provides, in general, an analytical performance better than that reported for other Fib immunosensors and commercial ELISA kits. This simple and relatively low cost immunosensor configuration permitted the sensitive and selective determination of Fib in human plasma and urine.

Lysosomal membrane permeabilization: carbon nanohorn-induced reactive oxygen species generation and toxicity by this neglected mechanism.

Understanding the molecular mechanisms responsible for the cytotoxic effects of carbon nanomaterials is important for their future biomedical applications. Carbon nanotubular materials induce the generation of reactive oxygen species (ROS), which causes cell death; however, the exact details of this process are still unclear. Here, we identify a mechanism of ROS generation that is involved in the apoptosis of RAW264.7 macrophages caused by excess uptake of carbon nanohorns (CNHs), a typical type of carbon nanotubule. CNH accumulated in the lysosomes, where they induced lysosomal membrane permeabilization (LMP) and the subsequent release of lysosomal proteases, such as cathepsins, which in turn caused mitochondrial dysfunction and triggered the generation of ROS in the mitochondria. The nicotinamide adenine dinucleotide phosphate oxidase was not directly involved in CNH-related ROS production, and the ROS generation cannot be regulated by mitochondrial electron transport chain. ROS fed back to amplify the mitochondrial dysfunction, leading to the subsequent activation of caspases and cell apoptosis. Carbon nanotubules commonly accumulate in the lysosomes after internalization in cells; however, lysosomal dysfunction has not attracted much attention in toxicity studies of these materials. These results suggest that LMP, a neglected mechanism, may be the primary reason for carbon nanotubule toxicity.

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.

Carboxylation of thin graphitic sheets is faster than that of carbon nanohorns.

Globular aggregates of carbon nanohorns (CNHs) often contain graphite-like thin sheets (GLSs), and providing different functions to CNHs and GLSs would expand the possible applications of the CNH-GLS aggregates. We show that the GLS edges can be carboxylated selectively by immersing the aggregates in an aqueous solution of H2O2 at room temperature for 1 hour. The presence of carboxyl groups was confirmed by temperature-programmed desorption mass spectroscopy measurements, and their amounts were evaluated using thermogravimetric analysis. The preferential carboxylation of GLSs at their edges was evidenced, after the carboxyl groups were reacted with Pt-ammine complexes, by electron microscopic observation of the Pt atoms at the GLS edges. Since few holes in CNH walls were opened by the short-period H2O2 treatment, there was little carboxylation of CNHs.

Size-dependent biodistribution of carbon nanohorns in vivo.

Carbon nanotubules, such as nanotubes and nanohorns, are potentially useful as drug delivery or hyperthermia agents for cancer therapy. However, the biokinetics of variously sized nanocarbons are important for their medical application and risk assessment. To examine the time course of the biodistribution of carbon nanohorns (CNHs) in mice, CNH aggregates of 100nm (L-CNHs) or CNHs of 30-50nm (S-CNHs) were dispersed with lipid polyethylene glycol and administered to mice through tail vein injection. Histological observation revealed that S-CNHs accumulated more slowly than did L-CNHs in the liver and spleen. The accumulation of L- and S-CNHs in spleen reached saturation within 1 and 48h, respectively, and the accumulation in liver reached saturation within 48h and >7days, respectively. CNHs did not accumulate appreciably in the lung, skin, or kidney. Histologic, hematologic, and immunologic (IL-6, TNF-α, and IFN-γ) tests did not reveal obvious toxicologic lesions at any time point. FROM THE CLINICAL EDITOR: In this study the biodistribution and accumulation characteristics of small and large carbon nanohorns were characterized in mice. Data demonstrate slower accumulation of small carbon nanohorns in liver and spleen, no accumulation in skin, lung, or kidney, and no obvious hematologic or immunologic toxicity.

Small-sized carbon nanohorns enabling cellular uptake control.

Carbon nanotubes perform well in preclinical tests for drug delivery and diagnostic imaging, but controlling the size at less than 100 nm to avoid nonspecific uptake by reticuloendothelial systems while targeting delivery to cells of interest via receptor-mediated endocytosis is difficult, which currently limits their widespread use. Herein, 20-50-nm graphene tubules, small-sized single-walled carbon nanohorns (S-SWNHs), are obtained with a yield of 20% or higher by an oxidative exfoliation of 100 nm pristine SWNH aggregates. S-SWNHs are highly hydrophilic and remarkably resistant to cellular uptake by macrophages (RAW 264.7 cells), tumor cells (HeLa or KB), or normal cells (FHs 173We). The nonstimulatory property to cell membranes therefore makes cellular uptake control of S-SWNHs by functionalization easy. By attaching phospholipid polyethylene glycol, the cellular internalization of S-SWNHs is almost completely inhibited in RAW 264.7 macrophages. When functionalized with tumor-targeting folic acid (FA), FA-S-SWNHs are taken up by FA receptor-overexpressing KB cells but not by normal human embryonic cells (FHs 173We), which do not express the FA receptor. With a high rate of stealth and targeting in vitro, S-SWNHs are one of the most promising nanoparticles for medical use.

Helicity in ropes of chiral nanotubes: calculations and observation.

Even though isolated defect-free single-wall carbon nanotubes are straight, bundles of chiral single-wall carbon nanotubes are often helical according to our observations using high-resolution electron microscopy. The driving force for the formation of such helices is the energy gain associated with the optimum orientational alignment of neighboring nanotubes. Our total energy calculations allow us to analyze the torsional and bending stress components in helical nanotube ropes and specify under which conditions straight nanotube bundles gain energy upon forming a helix.

Atomic imaging and spectroscopy of low-dimensional materials with interrupted periodicities.

Identification of individual atoms and examination of their electronic properties in materials are the ultimate goal of all microscopy-based analytical techniques. Here, we demonstrate successful single-atom imaging and spectroscopy in low-dimensional materials using (scanning) transmission electron microscopy together with electron energy-loss spectroscopy (EELS). Edges and point defects in single-layered materials such as graphene, hexagonal boron nitride and WS(2) nanoribbons are investigated by annular dark-field imaging and EELS fine-structure analysis. Individual dopant atoms are unambiguously identified in nano-peapods. It is noteworthy that irradiation damage and specimen contamination even at the single-atom level are crucial issues in these experiments.

Selective extraction of large-diameter single-wall carbon nanotubes with specific chiral indices by poly(9,9-dioctylfluorene-alt-benzothiadiazole).

Semiconducting single-wall carbon nanotubes (SWCNTs) having large diameters (d(t) > 1.3 nm) are successfully extracted in toluene by fluorene-based polymers. In particular, poly(9,9-dioctylfluorene-alt-benzothiadiazole) shows excellent selectivity for (15,4) SWCNTs. Although the importance of structural matching between the fluorene backbone and the tube surface has already been discussed, the present photoluminescence studies reveal that matching the energy levels between fluorene-based polymers and SWCNTs is crucial for selective nanotube extractions.

Confinement in carbon nanospace-induced production of KI nanocrystals of high-pressure phase.

An outstanding compression function for materials preparation exhibited by nanospaces of single-walled carbon nanohorns (SWCNHs) was studied using the B1-to-B2 solid phase transition of KI crystals at 1.9 GPa. High-resolution transmission electron microscopy and synchrotron X-ray diffraction examinations provided evidence that KI nanocrystals doped in the nanotube spaces of SWCNHs at pressures below 0.1 MPa had the super-high-pressure B2 phase structure, which is induced at pressures above 1.9 GPa in bulk KI crystals. This finding of the supercompression function of the carbon nanotubular spaces can lead to the development of a new compression-free route to precious materials whose syntheses require the application of high pressure.

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 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.

Histological assessments for toxicity and functionalization-dependent biodistribution of carbon nanohorns.

Single-walled carbon nanohorns (SWNHs) intravenously administered to mice did not show severe toxicity during a 26-week test period, which was confirmed by normal gross appearance, normal weight gain and the lack of abnormality in the tissues on histological observations of the mice. SWNH biodistribution was influenced by chemical functionalization. Accumulation of SWNH in the lungs reduced as SWNH hydrophilicity increased; however, the most hydrophilic SWNHs modified with bovine serum albumin (BSA) were most likely to be trapped in the lungs, suggesting that the BSA moiety enhanced macrophage phagocytosis in the lungs. Clearance of some of the hydrophobic SWNHs from the lungs was observed, the mechanism of which is briefly discussed.