Ryota Yuge

Site Identification of Carboxyl Groups on Graphene Edges with Pt Derivatives

Although chemical functionalization at carboxyl groups of nanocarbons has been vigorously investigated and the identities and quantities of the carboxyl groups have been well studied, the location of carboxyl groups had not previously been clarified. Here, we show that site identification of carboxyl groups is possible by using Pt-ammine complex as a stain. After Pt-ammine complexes were mixed with graphenes in ethanol, many Pt-ammine complex clusters with an average size of about 0.6 nm were found to exist at edges of graphene sheets, indicating that the carboxyl groups mainly existed at the graphene edges. These results will make it easier to add functionalities by chemical modifications for various applications of nanotubes and other nanocarbons.

Biodistribution and Ultrastructural Localization of Single-Walled Carbon Nanohorns Determined In Vivo with Embedded Gd2O3 Labels

Single-walled carbon nanohorns (SWNHs) are single-graphene tubules that have shown high potential for drug delivery systems. In drug delivery, it is essential to quantitatively determine biodistribution and ultrastructural localization. However, to date, these determinations have not been successfully achieved. In this report, we describe for the first time a method that can achieve these determinations. We embedded Gd(2)O(3) nanoparticles within SWNH aggregates (Gd(2)O(3)@SWNHag) to facilitate detection and quantification. Gd(2)O(3)@SWNHag was intravenously injected into mice, and the quantities of Gd in the internal organs were measured by inductively coupled plasma atomic emission spectroscopy: 70-80% of the total injected material accumulated in liver. The high electron scattering ability of Gd allows detection with energy dispersive X-ray spectroscopy and facilitates the ultrastructural localization of individual Gd(2)O(3)@SWNHag with transmission electron microscopy. In the liver, we found that the Gd(2)O(3)@SWNHag was localized in Kupffer cells but were not observed in hepatocytes. In the Kupffer cells, most of the Gd(2)O(3)@SWNHag was detected inside phagosomes, but some were in another cytoplasmic compartment that was most likely the phagolysosome.

Highly efficient field emission from carbon nanotube-nanohorn hybrids prepared by chemical vapor deposition.

Electrically conductive carbon nanotubes (CNTs) with high aspect ratios emit electrons at low electric fields, thus applications to large-area field emission (FE) devices with CNT cathodes are attractive to save energy consumption. However, the poor dispersion and easy bundling properties of CNTs in solvents have hindered this progress. We have solved these problems by growing single-walled CNTs (SWNTs) on single-walled carbon nanohorn (SWNH) aggregates that have spherical forms with ca. 100-nm diameters. In the obtained SWNT-SWNH hybrids (NTNHs), the SWNTs diameters were 1-1.7 nm and the bundle diameters became almost uniform, that is, less than 10 nm, since the SWNTs were separated by SWNH aggregates. We also confirmed that a large-area FE device with NTNH cathodes made by screen printing was highly and homogeneously bright, suggesting the success of the hybrid strategy.

A high poly(ethylene glycol) density on graphene nanomaterials reduces the detachment of lipid-poly(ethylene glycol) and macrophage uptake

Amphiphilic lipid-poly(ethylene glycol) (LPEG) is widely used for the noncovalent functionalization of graphene nanomaterials (GNMs) to improve their dispersion in aqueous solutions for biomedical applications. However, not much is known about the detachment of LPEGs from GNMs and macrophage uptake of dispersed GNMs in relation to the alkyl chain coverage, the PEG coverage, and the linker group in LPEGs. In this study we examined these relationships using single walled carbon nanohorns (SWCNHs). The high coverage of PEG rather than that of alkyl chains was dominant in suppressing the detachment of LPEGs from SWCNHs in protein-containing physiological solution. Correspondingly, the quantity of LPEG-covered SWCNHs (LPEG-SWCNHs) taken up by macrophages decreased at a high PEG coverage. Our study also demonstrated an effect of the ionic group in LPEG on SWCNH uptake into macrophages. A phosphate anionic group in the LPEG induced lower alkyl chain coverage and easy detachment of the LPEG, however, the negative surface charge of LPEG-SWCNHs reduced the uptake of SWCNHs by macrophages.

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.

Preparation and Characterization of Newly Discovered Fibrous Aggregates of Single-Walled Carbon Nanohorns.

Fibrous aggregates composed of radially assembled graphene-based single-walled nanotubules are prepared, named here as fibrous aggregates of single-walled carbon nanohorns (fib-CNHs), whose structure resembles that of chenille stems. The newly discovered fib-CNHs are 30-100 nm in diameter and 1-10 μm in length. The fib-CNHs show high dispersibility and conductivity. The fib-CNHs increase the advantages of nanocarbons in various fields.

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.

Intercalation Effect of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimetane Having Strong Electron Affinity in Self-Assembled Monolayers Composed of Charge Transfer Complex Prepared by Coadsorption and Layer-by-Layer Adsorption Methods

Charge transfer (CT) complex self-assembled monolayers (SAMs) on a gold substrate are prepared using layer-by-layer adsorption and coadsorption methods with mercapto-methyl-tetrathiafulvalene (TTF-CH2SH) and strong acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (TCNQF4), in comparison with TTF-CH2SH/TCNQ SAMs consisting of moderate acceptor TCNQ. The layer-by-layer method yields TTF-CH2SH/TCNQF4 SAMs with the coexistence of neutral TCNQF4 and anionic TCNQF4-, where the TCNQF4- anions are laid on the TTF layer with the TTF-CH2SH molecules standing perpendicular to the gold substrate. The neutral TCNQF4 molecules are stacked above the TCNQF4- anion layer. This is in contrast to the fact that TCNQ having intermediate strength of acceptor character does not yield any CT SAMs when using the layer-by-layer technique. In the coadsorption method, TTF-CH2SH/TCNQF4 SAMs are formed, where all the TCNQF4 molecules are completely reduced as TCNQF4- anions, similar to those in bulk TTF-TCNQF4 crystals. Taking into account that TTF-CH2SH/TCNQ SAMs have the same fractional value (0.6) of the degree of charge transfer to that of bulk TTF-TCNQ crystal, the coadsorption technique can reproduce the electronic structure of the bulk CT complex in the 2D SAMs. The coadsorbed SAMs have an intercalation structure, where acceptor molecules are intercalated into the interstitials of TTF-CH2SH/Au units with the molecular axes of both acceptor and donor molecules parallel to each other. Such a donor/acceptor molecular arrangement can provide a favorable situation in the charge transfer between the two ingredients, resulting in the similar electronic structure to that of bulk CT crystals.

Ultrastructural localization of intravenously injected carbon nanohorns in tumor

Nanocarbons have many potential medical applications. Drug delivery, diagnostic imaging, and photohyperthermia therapy, especially in the treatment of tumors, have attracted interest. For the further advancement of these application studies, the microscopic localization of nanocarbons in tumor tissues and cells is a prerequisite. In this study, carbon nanohorns (CNHs) with sizes of about 100 nm were intravenously injected into mice having subcutaneously transplanted tumors, and the CNHs in tumor tissue were observed with optical and electron microscopy. In the tumor tissue, the CNHs were found in macrophages and endothelial cells within the blood vessels. Few CNHs were found in tumor cells or in the region away from blood vessels, suggesting that, under these study conditions, the enhanced permeability of tumor blood vessels was not effective for the movement of CNHs through the vessel walls. The CNHs in normal skin tissue were similarly observed. The extravasation of CNHs was not so obvious in tumor but was easily found in normal skin, which was probably due to their vessel wall structure difference. Proper understanding of the location of CNHs in tissues is helpful in the development of the medical uses of CNHs.

PROPERTY OF SELF-ASSEMBLED MONOLAYERS OF LONG-ALKYL-CHAIN-SUBSTITUTED TTF DIRIVATIVE

Self-assembled monolayers (SAMs) of an electron donor TTF derivative with long alkyl chains (-C11H22-) are formed on Au (111). STM, surface plasmon resonance, and FTIR reflection absorption spectroscopy measurements suggest that TTF backbone is isolated from the gold substrate by long alkyl chains. Cyclic voltammograms reveal two redox peaks (E1 1/2=263 mV, E2 1/2=508 mV vs. Ag/Ag+) corresponding to TTF/TTF+ and TTF+/TTF2+. These peak currents are proportional to the scan rates, indicating that the TTF backbone maintains its electrochemical activity in the SAMs. In addition, the peak-to-peak separations between oxidation and reduction are roughly proportional to the scan rates, which indicates that a potential drop takes place at the long alkyl chains, which work as resistance in the electron transport.