Michihiko Nakano

Single-molecule PCR using water-in-oil emulsion.

Polymerase chain reaction (PCR) using a single molecule of DNA is very useful for analysis, detection and cloning of the desired DNA fragment. We developed a simple PCR method utilizing a water-in-oil (W/O) emulsion that included numerous droplets of reaction mixture in bulk oil phase. These droplets, which were stable even at high temperatures, functioned as micro-reactors. This allows the effective concentration of template DNA to be increased, even for low concentrations of template DNA. The present method consists of a two-step thermal cycle. The first step was carried out using the W/O emulsion. During this step, the template DNA was amplified in the limited volume of the droplets in the W/O emulsion. The W/O emulsion was broken and the second PCR step was carried out. This method can be easily applied to amplify a single DNA molecule.

Development of rapid oral bacteria detection apparatus based on dielectrophoretic impedance measurement method

In this study, a bacteria detection apparatus based on dielectrophoretic impedance measurement (DEPIM) method was demonstrated for rapid evaluation of oral hygiene. The authors integrated a micro electrode chip on which bacteria were captured by dielectrophoresis (DEP), an AC voltage source to induce DEP force, and an impedance measurement circuit to a portable instrument that enables rapid and automated oral bacterial inspection in hospitals and clinics. Special considerations have been made on effects of high electrical conductivity of oral samples on DEP force and DEPIM results. It was shown experimentally and theoretically that using a higher electric field frequency for the DEP bacteria trap and the impedance measurement could realise DEPIM application to bacteria inspection from oral samples with higher conductivity. Based on these investigations, the authors optimised the frequency condition of the DEPIM suitable for inspecting an oral sample along with the design and development of a portable DEPIM apparatus for on-site inspection of oral bacteria. Under the optimised frequency condition, DEPIM results were in good agreement with the conventional culture method showing significant applicability of the DEPIM apparatus for practical rapid oral bacteria inspection.

Development of an Optoelectrostatic Micropump Using a Focused Laser Beam in a High-Frequency Electric Field

In this paper, fluid flow generated by laser irradiation in a high-frequency electric field was investigated with a view to using it as the driving force for a micropump. We discovered an optoelectrostatic phenomenon known as optoelectrostatic microvortex (OEMV) ten years ago. The OEMV is generated around the focal point of a laser beam located in the center of an intense high-frequency electric field. The direction of the opposed flow is parallel to the ac electric field and perpendicular to the sides of the electrodes. In this paper, the laser focus was positioned near one of the electrodes. One-directional flow was generated toward the other electrode. This flow was generated in a microchannel by simultaneous application of an Nd:YAG laser (1064 nm) and an ac voltage. The flow velocity increased with both increasing laser power and increasing ac voltage. In addition, the flow velocity was affected by the ac frequency. The flow velocity around the focal point was several hundred micrometers per second. At a distance of 3 mm from the laser spot, a flow velocity of 25 mum/s (0.74 muL/s) was observed

Electric fields and corona currents in needle-to-meshed plate gaps

This paper is aimed at evaluating the electric field, the corona onset voltage and the corona current in negatively stressed needle-to-meshed plate gaps as compared with the case of using a flat plate. The charge simulation method is used for calculating the electric field in the gap. The onset voltage is evaluated based on the calculated field and the criterion for self-recurring single electron-avalanches in the ionization-zone around the needle tip. The corona current?voltage characteristics were measured for thin and thick needles at two gap spacings with meshed and flat plates. The corona currents with meshed plates are lower than those with a flat plate; even the corona onset voltage with the flat plate is higher than that with the meshed plate.

Corona-induced pressures, potentials, fields and currents in electrostatic precipitator configurations

This paper is aimed at assessing analytically the dc corona induced pressures in wire-cylinder and wire-plate electrostatic precipitator configurations. This calls for solving the equations describing the corona discharge and the force balance for static gas equilibrium provided that the corona onset voltage and the space-charge-free field values are calculable. The calculated pressure and potential distributions along the gap axis in air and nitrogen at atmospheric pressure agreed well with those measured previously. The calculated corona current density values agreed reasonably with those measured for a high-temperature high-pressure wire-cylinder precipitator. The analytically calculated positive and negative dc corona onset voltages for wire-duct precipitators following proposed criteria based on discharge physics are in good agreement with those measured experimentally at atmospheric and lower pressures.

One-end immobilization of individual DNA molecules on a functional hydrophobic glass surface.

Abstract We demonstrate an effective method for DNA immobilization on a hydrophobic glass surface. The new DNA immobilizing technique is extremely simple compared with conventional techniques that require heterobifunctional crosslinking reagent between DNA and substrate surface that are both modified chemically. In the first process, a coverslip was treated with dichlorodimethylsilane resulting in hydrophobic surface. γ DNA molecules were ligated with 3′-terminus disulfide-modified 14 mer oligonucleotides at one cohesive end. After reduction of the disulfide to sulfhydryl (thiol) groups the resulting thiol-modified γ DNA molecules were reacted on silanized coverslip. Fluorescent observation showed that the thiol-modified γ DNA molecules were anchored specifically to the hydrophobic surface at one terminus, although non-specific binding of the DNA molecules was suppressed. It was observed that the one-end-attached DNA molecule was bound firmly to the surface and stretched reversibly in one direction when a d.c. electric field was applied.

Detection of SF 6 decomposition products generated by DC corona discharge using a carbon nanotube gas sensor

This paper describes application of carbon nanotube (CNT) gas sensor to detection of SF6 decomposition products generated by positive or negative DC corona discharge. The present authors have demonstrated CNT gas sensor-based partial discharge (PD) detection, aiming to develop a new diagnosis method of gas-insulated switchgear (GIS) filled with high pressure SF6 gas. In our previous studies, PD was generated by ac high voltage because most of GIS are designed and operated for conventional high voltage ac (HVAC) power transmission lines. In recent years, however, the electrical power industry has shown a trend shifting from HVAC to high voltage dc (HVDC) power transmission, which has many advantages such as higher power capacity and lower power loss. This technological trend motivated us to explore and expand the application of CNT gas sensor to detection of SF6 decomposition products generated by dc corona discharges. It was found that the CNT gas sensor exhibited significant response to dc corona discharge depending on the voltage polarity. In order to elucidate the mechanism of the polarity effect, SF6 decomposition products were analyzed by Fourier transformation infrared (FTIR) spectroscopy as well as using a gas detection tube. Based on comparison between the polarity effects on the CNT sensor response and the decomposition products, a possible contribution of HF to the CNT gas sensor response was suggested.

An array of interdigitated parallel wire electrodes for preparing a large-scale nanocomposite film with aligned carbon nanotubes

Application of high electric field is effective for the alignment of carbon nanotube (CNT) in a nanocomposite film. The conventionally used single pair of parallel plate electrodes is not applicable to large-sized nanocomposite fabrication due to limited output voltage of the high-voltage source. We have proposed an array of parallel wire electrodes to address this issue. The composite material was spread over a thin dielectric layer placed on the wire electrodes. The high electric field region can be extended over a wider area just by increasing the number of electrode pairs. Discrete electric field distribution bordered by the wire electrodes was avoided by linearly oscillated motion of the composite film. A CNT/epoxy resin composite film with a size of 15 cm × 15 cm was successfully fabricated.

Rapid microbead-based DNA detection using dielectrophoresis and impedance measurement

Polymerase chain reaction (PCR) is a powerful tool for diagnostic procedures in bacterial and viral infections. The authors propose a new electrical technique for rapid detection of DNA amplified by PCR using dielectrophoresis (DEP) of microbeads. The method is based on dramatic alteration of DEP characteristics of microbeads caused by DNA labeling. DNA-labeled microbeads are trapped on a microelectrode under the action of positive DEP, whereas pristine ones are not. DEP-trapped microbeads are measured impedimetrically to realize rapid and quantitative detection of the amplified DNA. The validity of the proposed method was demonstrated by detection of PCR-amplified DNA of viruses.

Dielectrophoresis and dielectrophoretic impedance detection of adenovirus and rotavirus

The aim of this study is the electrical detection of pathogenic viruses, namely, adenovirus and rotavirus, using dielectrophoretic impedance measurement (DEPIM). DEPIM consists of two simultaneous processes: dielectrophoretic trapping of the target and measurement of the impedance change and increase in conductance with the number of trapped targets. This is the first study of applying DEPIM, which was originally developed to detect bacteria suspended in aqueous solutions, to virus detection. The dielectric properties of the viruses were also investigated in terms of their dielectrophoretic behavior. Although their estimated dielectric properties were different from those of bacteria, the trapped viruses increased the conductance of the microelectrode in a manner similar to that in bacteria detection. We demonstrated the electrical detection of viruses within 60 s at concentrations as low as 70 ng/ml for adenovirus and 50 ng/ml for rotavirus.