Hideya Nagata

Near-infrared laser-triggered carbon nanohorns for selective elimination of microbes

Carbon nanomaterials, such as carbon nanohorns and carbon nanotubes, have attracted considerable attention for their biomedical applications. We report here the first application of carbon nanohorns (CNHs) as potent laser therapeutic agents for highly selective elimination of microorganisms. This is the first report, supported by direct observations, of the highly selective elimination of yeast and bacteria (Saccharomyces cerevisiae and Escherichia coli) by employing molecular recognition element–CNH complexes and a near-infrared laser.

Carbon Nanotube–Polymer Composite for Light‐Driven Microthermal Control

Carbon nanotubes (CNTs) have attracted considerable attention because of their various applications. In particular, the development of functional CNT–polymer composites has been a hot research topic in the last years. However, contrary to many theoretical expectations, the physical potential of CNT–polymer composites has not been fully utilized because of the low dispersibility of CNTs in polymer matrices. Therefore, surface engineering of the CNTs is considered to be indispensable for exploiting their physical potential. Here, we present a novel organic-solvent-dispersible single-walled CNT (SWNT) complex that has good dispersibility in poly(dimethylsiloxane) (PDMS)—a model polymer matrix which represents an attractive material for lab-on-a-chip technologies, such as microor nanofabrication. Controlling the temperature of a reaction mixture on a chip is of particular importance for many such applications. A light-driven PDMS microchip that encapsulates the SWNT complexes was shown to be capable of ultrarapid temperature control in a microspace. Covalent and noncovalent functionalizations of SWNTs are useful techniques for improving the dispersibility of the nanotubes in organic solvents. Covalent functionalization, however, disrupts the one-dimensional electronic structure and the desirable optical properties of the SWNTs. The noncovalent approach, on the other hand, is considered to be a promising technique because it results in better retention of the electronic structure of the CNTs. We therefore synthesized a phospholipid, PL, bovine serum albumin, BSA, functionalized single-walled nanotube, SWNT, (PL– BSA–SWNT) complex by using a noncovalent technique (see Figure 1a and the Supporting Information for details). The BSA molecules bind noncovalently to the surface of the SWNTs through hydrophobic interactions, p–p interactions, and interactions via the amine functionalities of the protein. The hydrophobic alkyl chains of the PL increase the dispersibility of the BSA-functionalized SWNT (BSA– SWNT) complexes in both nonaqueous solvents and the PDMS polymer matrix. Pristine SWNTs and the BSA– SWNT complex are not dispersible in dichloromethane (Figure 1b, 1 and 2), whereas the PL–BSA–SWNT complex is readily dispersible in various organic solvents, but not in water (Figure 1b, 3–7). Bundle-free or isolated SWNTs have been reported to exhibit characteristic signals in the visible (Vis) and near-infrared (NIR) regions of their optical absorbance spectra as a result of van Hove transitions. The Vis/NIR optical absorption spectrum of a dispersion of the PL–BSA–SWNT complex in dichloromethane showed first metallic (M11) and second semiconducting (S22) bands in the ranges 440–600 nm and 550–800 nm, respectively (Figure 1c). In addition, we structurally characterized the PL– BSA–SWNT complex by means of atomic force microscopy Figure 1. Organic-solvent-dispersible SWNT complex. a) Image of the PL–BSA–SWNT complex. b) Photographs of dispersions of various SWNT constructs (1: SWNT, 2: BSA–SWNT, 3–7: PL–BSA–SWNT) in organic solvents (1–3: dichloromethane, 4: chloroform, 5: toluene, 6: ethyl acetate) and in water (7). c) Vis/NIR spectrum of a PL–BSA– SWNT/dichloromethane solution (350 mgmL ). d) AFM image of PL– BSA–SWNT complexes deposited on a mica substrate (left), and height profiles [nm] along lines 1–3 (right).

Photoinduced antiviral carbon nanohorns

Nanocarbons, such as carbon nanohorns (CNH) and carbon nanotubes, are materials of interest in many fields of science and technology because of their remarkable physical properties. We report here a novel approach for using NIR laser-driven CNH as an antiviral agent. NIR laser-driven functional CNH complexes could open the way to a new range of antiviral materials.

Light‐Driven Thermoelectric Conversion Based on a Carbon Nanotube–Ionic Liquid Gel Composite

The development of new energy power generators is one of the most important components of the efforts that address today’s energy problems. Thermoelectric conversion devices can directly convert thermal energy into electrical energy owing to temperature differences, and can act as power generators. 2] Using light energy to power thermoelectric devices is an interesting alternative energy source for the generation of power, and can simultaneously meet the demands for energy conservation without damaging the environment. Low-light absorbents, such as carbon black and black iron oxide, are typically used in solar-heat-driven thermoelectric conversion systems as a photo-exothermic material. Nanocarbon materials, such as carbon nanotubes (CNTs), carbon nanohorns, and fullerenes, have been of great interest to researchers over the past decade because of their unique physical and chemical properties. In particular, the photothermal property of nanocarbons is one of the most desirable characteristics for a variety of thermal applications. The light-triggered exothermy of the nanocarbons probably results from the optically stimulated electronic excitations of the carbon atoms being rapidly transferred owing to molecular vibration energies, thereby causing the generation of heat. Recently, we demonstrated that a near-infrared (NIR) laser-driven thermoelectric conversion module, based on a single-walled CNT (SWNT)–polyacrylamide (PAA) hydrogel composite, can operate as a thermoelectric convertor. However, this nanotube thermoelectric conversion system was poor at generating electrical power. This was largely attributed to the low thermal stability of the PAA hydrogel. Fukushima et al. recently reported SWNT–roomtemperature ionic liquid (RTIL) gel composites for use in electronics and as actuators. 16] RTILs, especially those based on the n-alkylimidazolium cation, are emerging as alternatives to the conventional organic solvents used in chemical processes. These environmentally friendly solvents have many useful properties, such as high thermal stability, high ionic conductivity, negligible vapor pressure, and a large electrochemical window. The use of RTILs as gel matrices for lightdriven thermoelectric convertors is interesting; the high thermal stabilities of the RTILs make it possible to obtain a photothermally very stable CNT-based gel composite for a lightdriven thermoelectric convertor. Herein, we report a NIR lasertriggered thermoelectric conversion system based on RTIL gel composites encapsulating SWNTs. Our improved CNT-based thermoelectric conversion devices, which have very high photothermal stabilities, should be useful for many industries, such as robotics and aerospace engineering. The concept of photoinduced thermoelectric conversion based on a CNT–RTIL gel composite is illustrated in Figure 1 a.

Use of a heterogeneous buffer combination in microchip electrophoresis for high-resolution separation by on-line concentration of DNA samples†

We have developed a novel high‐resolution separation technique of DNA fragments in a heterogeneous combination of a sample buffer and a separation buffer. The use of a heterogeneous buffer combination is a simple method for on‐line concentration of DNA fragments, in which a sample buffer is simply exchanged with one including taurine anions. The mobility of taurine anions, co‐ions for DNA, is lower than the that of acetate anions in a separation buffer. The difference in the mobility invokes transient isotachophoresis. The current technique allows DNA fragments to be effectively concentrated and the separation length of microchips to be shorter than that of conventional ones by a factor of three without deterioration in separation resolution and any modification of a chip design. Fragments of 100‐bp DNA ladders (100–1000 bp) were separated with high resolution (0.72–10.7) within 60 s with a 10 mm separation length on a polymethyl methacrylate chip. Furthermore, fragments of 10‐bp DNA ladders (10–330 bp) were separated with high resolution (0.69–2.00) with a 10 mm separation length within 50 s without band broadening. The current achievements will make it possible to fabricate compact devices for microchip electrophoresis.

Light-triggered thermoelectric conversion based on a carbon nanotube-polymer hybrid gel.

Lights? Nanotubes? Action! A hydrogel comprising lysozymes, poly(ethylene glycol), phospholipids, and functionalized single-walled carbon nanotubes is employed for light-driven thermoelectric conversion. A photoinduced thermoelectric conversion module based on the hydrogel functions as a novel electric power generator (see image). This concept may find application in various industries, such as robotics and aerospace engineering.

Sizing of single globular DNA molecules by using a circular acceleration technique with laser trapping.

We describe a method for in situ sizing individual huge DNA molecules by laser trapping. Single DNA molecules are reversibly transformed, without mechanical fragmentation of fragile huge-sized DNA, from their random coil state into their globular state induced by condensing agents poly(ethylene glycol) and Mg(2+). With the use of a globular DNA molecule folded by condensation, the critical velocity of the circularly accelerated single globular DNA molecule by laser trapping was found to be proportional to the size of the DNA. Yeast, Saccharomyces cerevisiae, chromosome III (285 kbp) was successfully sized (281 +/- 40 kbp) from a calibration curve scaled using lambda, T4, and yeast chromosome VI (48.5, 166, and 385 kbp, respectively). The use of critical velocity as a sizing parameter makes it possible to size single DNA molecules without prior conformational information, i.e., the radius of a single globular huge DNA molecule as a nanoparticle. A sized single globular DNA molecule could be trapped again for subsequent manipulation, such as transportation of it anywhere. We also investigated a possibility of reusing the globular DNA molecules condensed by PEG and Mg(2+) for PCR and found that PCR efficiency was not deteriorated in the presence of the condensation agents.

Development of PC-controlled laser manipulation system with image processing functions

Laser manipulation is an important technique suitable for controlling objects in liquid at length scales ranging from sub-micrometers to micrometers. However, the use of this technique by itself is not enough to dexterously or automatically manipulate objects. In this article we propose a concept for automated non-contact micro-manipulation combined with laser manipulation and advanced control system techniques, and describe the configuration of a developed system, i.e. a three-beam laser trapping system with excellent user-interfaces, real-time image processing functions and a micro-laser ablation beam. We also show the results of several demonstrations; namely the arrangement of metallic particles, the manipulation of a non-spherical object, the laser perforation of a cell, and the automated selection and transportation of colored micro beads.