Toshio Ogino

Site-specific gene transfer with high efficiency onto a carbon nanotube-loaded electrode.

A transfection array, which is specifically developed for use in high-throughput analyses of genome functions by the over-expression or suppression of genes on a chip, is expected to become an important method for post-genome research. High efficiency of gene expression or suppression is indispensable for high-throughput analyses because the adherent cell number on a single spot decreases as the density of spots increases in the transfection array. We have studied an electro-stimulated pore formation on the cell membrane for gene delivery. Fine pores should be formed on the cell membrane to increase the efficiency of gene transfection without cell damage. Herein, we examined the electrode carrying chemically functionalized carbon nanotubes (CNTs) on the surface. The CNTs were loaded on a gold electrode with a self-assembled monolayer membrane by electrostatic interaction. Adsorbed plasmid DNA was transfected with higher efficiency into adherent cells on the CNT-loaded electrode than on an electrode without CNTs. This result may be due to the strong but fine field emission formed from the tips of the CNTs.

Electric Property Control of Carbon Nanotubes by Defects

Effects of local low-energy irradiation on the electric properties of metallic single-walled carbon nanotubes were studied. Defects formed by 20 keV-electron irradiation in an electron beam lithography system converted the room-temperature electric properties to p-type or ambipolar semiconducting. Coulomb oscillation was also observed at room temperature. The results also suggest that electric measurements are inconclusive for distinguishing whether a nanotube is metallic or semiconducting.

Ultrahigh vacuum scanning electron microscope system combined with wide-movable scanning tunneling microscope

A surface analysis system has been newly developed with combination of ultrahigh vacuum scanning electron microscope (SEM) and wide-movable scanning tunneling microscope (STM). The basic performance is experimentally demonstrated. These SEM and STM images are clear enough to obtain details of surface structures. The STM unit moves horizontally over several millimeters by sliding motion of PZT actuators. The motion resolution is proved to be submicrometers. The STM tip mounted on another PZT scanner can be guided to a specific object on the sample surface during SEM observation. In the observation of a Si(111) surface rapidly cooled from high temperature, the STM tip was accurately guided to an isolated atomic step and slightly moved along it during SEM observation. The STM observation shows an asymmetry of the (7×7)-transformed region along the step between the upper and lower terraces. (7×7) bands continuously formed along the edge of terraces, while (7×7) domains distributed on the terraces slightly far...

Morphology of Carbon Nanostructures in Alcohol Chemical Vapor Deposition

We have investigated the growth of carbon nanocoils (CNCs) using a combination of a Ni catalyst and alcohol chemical vapor deposition (CVD). When using an Fe or Co catalyst, only normal carbon nanotubes (CNTs) are grown at 700 and 900 °C. On the other hand, when using a Ni catalyst, CNCs with various helical structures are grown at 900 °C in addition to CNTs. When a Ni/Fe or Ni/Co alloyed catalyst is used, the yield of the CNCs decreases and the shape of the CNCs becomes elongated as the Fe or Co content increases. These results will contribute to our understanding of the CNC growth mechanism.

Characterization of Mechanical Properties of Suspended Carbon Nanotubes in Liquid

In this paper, we describe the mechanical interaction between the vibrating tip of an atomic force microscope (AFM) and carbon nanotubes (CNTs) suspended over a trench on a Si wafer. The interaction was detected by recording the oscillation amplitudes of the cantilever tip above the suspended CNTs during both tip-down and tip-up processes. We refer to the oscillation amplitude versus tip vertical position as a force curve. In the force curve obtained in air, the mechanical response of a CNT bundle under a periodic external force applied by the tip is interpreted as a simple model that includes the attachment/detachment of the CNTs onto the tip surface and the oscillation of the CNTs fixed to the tip. The curve obtained in water has features similar to that obtained in air. The difference between the force curves obtained in air and in water suggests that the adhesion force between the AFM tip and CNTs is weaked in water than in air.

Construction of carbon nanotube networks using ferroin solution

We investigate methods of fabricating a distinctive structure on a silicon substrate to grow a carbon nanotube network using a dried ferroin solution. A dried ferroin solution forms fissure structures on the substrates. The fissure structures have unique shapes and iron particles that act as catalysts for growing carbon nanotubes. Such structures should be suitable for fabricating 3D carbon nanotube networks. To confirm this, we use a thermal CVD of a hydrogen-methane gas system to grow carbon nanotubes on the structures. The density of carbon nanotube networks grown on the substrates seems to be higher when the concentration of the ferroin solution is stronger. Results indicate that the dried ferroin solution can not only produce distinctive structures for carbon nanotube growth as expected, but also control the growth.

Fabrication of carbon nanotube thin films by surface engineering

We have investigated uniform carbon nanotube (CNT) dispersion in a solution and fabrication of CNT thin films on solid surfaces. To prevent bundle formation, we have examined surface modification of both the CNT surfaces and the substrate surfaces. To enhance the interaction between surfaces of the substrate and the CNTs, the substrate surfaces were made hydrophobic, because CNTs are generally hydrophobic. When CNTs were dispersed on the hydrophobic surfaces, relatively uniform CNT thin films were formed. To weaken the interaction between the individual CNTs, CNT surfaces were coated with synthetic polymers or biomolecules. Amphiphilic, ionic polymers with pi-stacking are most suitable for CNT solubilization in a polar solvent. High-density well-dispersed CNT thin films were fabricated by modifying CNT surfaces with single-stranded DNAs.

Effect of Chemical Modification of the Substrate Surface on Lipid Bilayer Formation

Bio-compatible surfaces and interfaces are required in the functional analysis of living cells and biological molecules as well as in their application to various biotechnological devices because those cells and molecules have to be immobilized on the solid surfaces without danaturation of the bioactivities. To fabricate bio-compatible interfaces, control of the initial solid surfaces is crucial. Cell surfaces consist of a lipid bilayer and membrane proteins. The reserch on membrane proteins is important in application to biochips and biosensors. Artifical lipid bilayers are often used as a model system of the cells in in vitro studies of the fundamental properties of the membrane proteins.. For fomation of lipid bilayers, we used vesicle fusion method illustrated in Fig. 1. Lipid bilayers, which consist of two amphiphilic phospholipid layers formed in polar solution, are formed by fusion and expansion of the vesicles. In the formation process, hydrophilic and/or hydrophobic interactions between the vesicles and the substrate surface are essential. Generally the surface control includes structural and chemical approach. In the formation of uniform low-defect bilayers, the chemical state control plays more important role. We focused on the chemical controls of the substrate surfaces, in particular control of hydrophilicity and/or hydrophobicity of the surfaces. We also examined the effect of surface charge by modifying the surfaces with various self-assemble monolayers (SAMs).