Table of contents

Control over electron-spin states, such as coherent manipulation, filtering and measurement promises access to new technologies in conventional as well as in quantum computation and quantum communication. In this paper, we review recent theoretical proposal of using electron spins in quantum confined structures as qubits. We also present a theoretical proposal for testing Bell's inequality in nano-electronics devices. We show that the entanglement of two electron spins can be detected in the spin filter effect in the nanostructure semiconductor/ferromagnetic semiconductor/semiconductor junction. In particular, we show how to test Bell's inequality via the measurement of the current-current correlation function in this setup.

Results of spin-related transport observed in various one-dimensional (1D) samples made at high In-content InGaAs/InAlAs modulation-doped hetero-junctions are reported. This type of material is interesting especially from the view point of non-magnetic semiconductor spintronics, since it contains two-dimensional electron gas (2DEG) which reveals large spin–orbit coupling constant (α) as well as very high electron mobility (μ_e) at low temperatures. 1D structures studied here are diffusive narrow wires (width, w) and quantum point contacts (QPCs) as typical example of ballistic transport regime. In the long diffusive wires with a variety of width, α is found to remain unchanged when w>2 μm. But in the diffusive wires with side-gate (the width of the wire can thus be controlled by the side-gate voltage), α is enhanced by applying negative voltage to the side gate. This is probably due to that the side-gate voltage has enhanced asymmetric lateral electric field perpendicular to the moving direction of 2DEG. In the QPC samples defined by the wire and the finger side-gate, conductance quantization in unit of 0.5(2e²/h) is confirmed. This might be caused by the formation of 'spin-related Tomonaga–Luttinger wire', which encourages spin-polarized transport in such an ideal conductor. Finally, we propose several quantum information processing devices based on the spin-FET, that could construct a solid-state qubit and quantum computation devices and circuits.

We investigated the transport properties of ferromagnetic/semiconductor hybrid structures utilizing an InAs/In_0.75Al_0.25As modulation-doped heterostructures formed on a GaAs (001) substrate with In_xAl_1−xAs step-graded buffer layers. We used NiFe as ferromagnetic electrodes for injection/detection of spin-polarized electrons, which were formed on side walls of the semiconductor mesa to contact electron channel directly. We measured magneto-transport properties of the samples with current flow between the ferromagnetic electrodes at low temperatures. Under vertical magnetic fields, magneto-resistance oscillations were clearly observed, thus the ferromagnetic electrodes worked as ohmic contacts. In addition, we successfully found spin-valve properties under parallel magnetic fields. Furthermore, we observed the enhancement of spin-valve properties by squeezing the channel width.

We systematically studied spin–orbit interaction in narrow wires with different wire widths, where the base material is a normal-type In_0.75Ga_0.25As/In_0.75Al_0.25As modulation-doped narrow-gap heterojunction. We used two different methods to make the wires and analyze their spin-dependent transports. As a first method, the wire width was defined by simply mesa-etching the samples on the same substrate. As a second method, we fabricated wire samples with side-gate. The wire width was changed by varying a voltage applied to the side-gate. For the determination of spin–orbit coupling constant, α, we measured magneto-resistance at 1.6 K. In the first method, α remained almost constant in the wires with various widths longer than 0.4 μm. However, in the second method, α increased with decreasing the wire width down to about 1 μm. The increase of α observed in the side-gate structure sample might rather be attributed to the effect of the lateral electric field by the side-gate, which could enhance the effect of the vertical electric field originally existing at the hetero-interface.

Oxyfluoride glasses were developed with composition 30SiO₂·15AlO_1.5·28PbF₂·22CdF₂·(4.9−x)GdF₃·0.1HoF₃·xYbF₃ (x=0, 0.1, 0.2, 0.5, 1, 2, 3, and 4) in mol%. Powder X-ray diffraction analysis revealed that the heat-treatments of the oxyfluoride glasses at the first crystallization temperature cause the precipitation of Yb³⁺–Ho³⁺ co-doped fluorite-type nano-crystals of about 17.8 nm in diameter in the glass matrix. These transparent glass-ceramics exhibited very strong green up-conversion luminescence due to the Ho³⁺: (⁵F₄, ⁵S₂)→⁵I₈ transition under 980 nm excitation. The intensity of the green up-conversion luminescence in the glass-ceramics was much stronger than that in the precursor oxyfluoride glass. The reasons for the highly efficient Ho³⁺ up-conversion luminescence in the oxyfluoride glass-ceramics are discussed.

Diffraction efficiency and morphology of holographic gratings were improved by combining ring-opening polymerizable epoxides with radical polymerizable conventional acrylate systems. By adding epoxide materials, the grating spacings were increased when compared with the case where only acrylate was used. The effects were especially notable for cyclohexane oxide derivatives. The diffraction efficiency was the highest, and nanoscale phase-separated liquid crystal domains were the most clearly formed using siloxane-containing cyclohexane oxide group, due to their incompatibility and fast curing.

Aluminum (III) tris[2-(2-hydroxyphenyl)-5-phenyl-1,3-oxazole] (Alppo₃), has been synthesized as a new efficient blue electroluminescent (EL) material. Alppo₃ provided good color purity, high luminance, and high efficiency of blue light-emission in an organic light-emitting device. The EL maximum wavelength is 420 nm and Commission Internationale de l'Eclairage coordinates are x=0.16, y=0.15 of blue color chromaticity. The luminance efficiency and the maximum luminance of Alppo₃ device were 3 lm/W at 6.05 mA/cm² (345 cd/m²) and 13,900 cd/m², respectively.

Improved lifetime with enhanced efficiency of an Alq₃ based OLED was realized by the co-evaporation of hexamethylbenzene (HMB). Two different solvated crystalline systems of Alq₃, Alq₃(C₇H₈)_1/2, Alq₃(C₂H₅OH), were synthesized to investigate the effect of optically inactive materials on the emission properties of Alq₃. Clathrate solvents perturb the excited electronic states of Alq₃ so that the incorporated materials in OLEDs should be chemically and optically inactive to control polymorphs. HMB acts as a carrier blocker for both electrons and holes. However, Alq₃ may be stabilized from Joule heat if the Joule heat is efficiently consumed as the vibrational/rotational energy of HMB. Consequently, the self-quenching and the crystallization of Alq₃ are effectively suppressed by the HMB, resulting in prolonged operating time and enhanced efficiency for Alq₃-OLEDs.

Proteins are prone to aggregate at high temperature. In order to investigate the heat-induced aggregation, Concanavalin A (Con A) was used as a model protein because disulfide formation doesn't occur throughout the aggregation process. With increasing temperature, fluorescence intensities of 8-anilino-1-naphthalenesulfonate (ANS) and thioflavin T (ThT) showed a maximum at around 45–50 °C. After the heating, the fluorescence intensities increased with decreasing temperatures. The enhancement of the fluorescence during cooling implies that the heat-induced aggregates of Con A possess porosity on this surface allowing the binding to fluorescent probes.

This study describes the optimization of fluorescent cell-based assays using microchamber array chip formats as well as using automatic nanoliter volumes of sample dispensing system for high-throughput screening analysis of anticancer drugs. Cell-based assays can be employed efficiently in the screening of potential anticancer drug candidates and bioactive compounds with distinct biological function. Identification and development of cell-based assays adapted to high-throughput screening requirements is important when screening chemicals for their potential anticancer properties. Cell-based screening assays using microchamber array chip formats and automatic nanoliter volumes of sample dispensing system requires an optimization as a prerequisite for parameters including assay liquid volume and number of cells per each chamber, and the total cell-based assay itself. Further, the anticancer effect of mitomycin C was studied as an example against human cervical carcinoma cell line-HeLa 229 using cell-based assay that was optimized on chamber array chip formats and determined the cytotoxicity of mitomycin C by measuring the cell proliferation of HeLa with Calcein-AM fluorescent dye. The cell-based screening assay that was performed using chamber array chip formats was compared with the conventional 96-well plate formats was discussed. The assay described in this study is rapid, simple and inexpensive that is desirable in selecting anticancer candidates.

The specific binding of peptide nucleic acid (PNA) to its complementary DNA target is combined with magnetic separation to enable discrimination against single nucleotide polymorphisms (SNP). PNA probes with biotin label at 5'-end were attached to strepavidin coated superparamagnetic iron oxide beads. PNA modified beads were then challenged with non-complementary, SNP containing and perfect-match DNA targets. PNA probe showed no affinity towards non-complementary DNA. The non-specific binding of SNP containing DNA target was suppressed by the washing step of the beads by using sodium dodecylsulfate in blank buffer solution. Then, an electro-active intercalator, 7-dimethyl-amino-1,2-benzophenoxazinium salt (Meldola's blue, MDB) was introduced to the beads. MDB intercalated between the double-helix of the hybrid molecules on the beads. After removing the excessive MDB, the beads were collected from the solution by immersing a biotin modified carbon paste electrode into the solution. Specific hybridization between PNA probe and DNA target was determined by monitoring the voltammetric peak of MDB. Numerous factors affecting the MDB signal, such as target DNA concentration, intercalator concentration and accumulation time were investigated. MDB signal indicated a detection limit of 2 pM in connection with 20 min hybridization time.

Oigonucleotide microarrays (DNA chips) are very efficient tools to analyze genotypes of patients or change in gene expressions between two different samples. However, there is no cost effective procedure to manufacture DNA chips. We are developing 'probe-on-carriers', immobilized oligonucleotide probes on solid phase to make DNA chips. In this procedure, each oligonucleotide is synthesized on a controlled porous glass carrier as a solid phase, and can be used as a probe for each sequence. This can be substantiated by technology for strictly controlled pore-size of porous glass. In fact, we found the sequence specific hybridization of probe-on-carrier with using porous glass of larger than 50 nm pore diameter.

The probe-on-carriers for wildtype and mutant p53 genes were hybridized with their complementary probes, respectively, but not with another probes. This result clearly demonstrated that the probe-on-carriers could recognize one-nucleotide substitutions of a gene. We found that the fixed probe-on-carriers on a slide glass still showed sequence specific hybridization. Therefore, we conclude that the probe-on-carriers are epoch-making materials for making DNA chip economically.

Aminoethylcarbamoyl-polyrotaxanes (AEC-α/E35-TYR-Zs) were synthesized as a novel cationic polymer for DNA complexation and characterized in terms of physicochemical properties of polyion complex. Here, AEC groups were introduced to hydroxyl groups of α-cyclodextrins (α-CDs) that are threaded onto a poly(ethylene glycol) (PEG) chain capped with bulky end-groups (polyrotaxane). We examined the ability of DNA complexation of the AEC-α/E35-TYR-Zs compared with polyethylenimine (PEI). Agarose gel shift assay and ethydium bromide (EB) displacement analysis showed that the number of threading α-CDs was one of the dominant factors to enhance the ability of DNA complexation. In addition, increasing the number of AEC groups in the AEC-α/E35-TYR-Zs led to tighter complexation.

Through layer-by-layer adsorption (LBL) technique, multilayer film was prepared from enzymes, diaphorase (DI) and glucose-6-phosphate dehydrogenase (G6PDH) and polyelectrolytes. The adsorption interface morphology was directly observed by atomic force microscopy, and the immobilization amount and layer thickness were characterized from quartz crystal microbalance which showed formation of nanoscale multilayer structure and linear mass increase which depended on alternate adsorption cycles. In order to construct a new mediated bi-enzyme biosensor system, polymerized mediator, DI and G6PDH were immobilized on carbon electrode surface by using LBL method. Electrochemical experiments indicated highly efficient electron transfer by the polymerized mediator. Two enzymes kept their activities after immobilization, and the electrode immobilized by mediator and enzymes showed sensitive response to glucose-6-phosphate in the presence of free NAD⁺, and high stability during long period of storage.

Plants, like other organisms, have adaptive mechanisms whereby they are able to respond to both nutrient deficiencies and toxicities. Phytochelatins (PCs) play an essential role in heavy-metal detoxification in plants, fungi and worms. PCs chelate heavy metals and then PC-metal complexes are translocated across the tonoplast and sequestered in vacuoles. PCs are synthesized from glutathione by the enzyme PC synthase (PCS). Comparison of the deduced amino acid sequences of PCS suggests that the C-terminal domain may be important for activation of the enzyme. We established the method for purification of PCS from Arabidopsis thaliana to perform enzymatic characterization. Moreover, the PCS gene was expressed in E. coli and S. cerevisiae to enhance tolerance to toxicity of cadmium ion. The obtained results implied that the some regions of the PCS may serve as regulatory region through interaction with cadmium ion and/or oxygen related compounds. Moreover, PCS expression dramatically enhanced cadmium ion tolerance of different organisms. Based on our findings, functional mechanism for PCS activation was hypothesized.

The structures of CPI-17 (Protein kinase-C dependent protein phosphatase-1 (PP1) inhibitor of 17 kDa) in an inactive and an active form have been determined by multidimensional NMR spectroscopy. Comparison of the two structures revealed how the molecular switch turns on at atomic resolution. Using the NMR structure of CPI-17 in the active form, the binding with catalytic domain of PP1 (PP1c) was simulated and the binding model is proposed in this report. When the phospho-Thr38 docks to the catalytic site of PP1, possible interactions for the tight binding are found; one is electrostatic interaction between a negatively charged cluster on phospho-CPI-17 and an acidic groove of PP1c, and the other is hydrophobic interaction between a hydrophobic surface area of phospho-CPI-17 and a hydrophobic groove of PP1c.