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Mitsuru Ishikawa

Publications and source records attributed to Mitsuru Ishikawa.

At least 19 recordsLinked to original sources
PubMed2007

Polarization modulation imaging ellipsometer.

The polarization modulation technique was successfully combined with parallel synchronous detection using a switching light source and a CCD camera to realize full-frame measurement of ellipsometric parameters. The detected thickness of a monolayer film of n-octadecylsiloxane agreed well with theoretical and reported experimental values. The thickness resolution for imaging and the temporal noise in parallel thickness measurements were smaller than +/-0.1 nm and smaller than +/-0.02 nm, respectively.

Biophysical Phenomena↗
PubMed2006

Quenching of photoluminescence in conjugates of quantum dots and single-walled carbon nanotube.

Development of quantum dot (QD) based device components requires controlled integration of QDs into different photonic and electronic materials. In this regard, introduction of methods for regular arrangement of QDs and investigation of properties of QD-based assemblies are important. In the current work we report (1) controlled conjugation of CdSe-ZnS QDs to sidewall-functionalized single-walled carbon nanotube (SWCNT) templates (2) and the effect of conjugation of QDs to SWCNT on the photoluminescence (PL) properties of QDs. We identified that PL intensity and lifetime of QDs are considerably reduced after conjugation to SWCNT. The origin of the quenching of the PL intensity and lifetime was discussed in terms of Förster resonance energy transfer (FRET). FRET involves nonradiative transfer of energy from a photoexcited QD (energy donor) to a nearby SWCNT (energy acceptor) in the ground state. This was examined by varying the density of QDs on SWCNT and conjugating smaller and bigger QDs to the same SWCNT. We estimated the FRET efficiency in QD-SWCNT conjugates from the quenching of the PL intensity and lifetime and identified that FRET is independent of the density and type of QDs on SWCNT but inherent to QD-SWCNT conjugates.

Carbon↗
PubMed2006

Usefulness of the 5' region of the cDNA encoding acidic ribosomal phosphoprotein P0 conserved among rats, mice, and humans as a standard probe for gene expression analysis in different tissues and animal species.

Housekeeping genes are often used as internal standards for gene expression analysis. When steady-state transcript levels of 4 typically used housekeeping genes, i.e., beta-actin, glyceraldehyde 3-phosphate dehydrogenase, cyclophilin, and acidic ribosomal phosphoprotein P0 (36B4), were evaluated in various rat tissues, the 36B4 gene seemed to be the most suitable as a standard to compare the expression levels of genes among different tissues. Next, for possible quantitative comparison of the expression level of this gene among different animal species, we compared the nucleotide sequence of the cDNA of 36B4 among rats, mice, and humans. As a result, highly conserved regions showing more than 97.5% identities were observed in the 5' portion of its open reading frame. When samples of synthesized mRNA encoding rat, mouse, and human 36B4 were hybridized with the entire cDNA encoding rat 36B4 as a probe, hybridization signals of mRNAs of mouse and human 36B4 were much weaker than those of mRNA encoding rat 36B4. However, when they were hybridized with an oligonucleotide probe corresponding to the highly conserved regions, they showed similar signal intensities. Thus, these highly conserved regions of the cDNA encoding 36B4 were concluded to be an effective standard for use in gene expression analysis.

Animals↗
PubMed2006

Variations in steady-state and time-resolved background luminescence from surface-enhanced resonance Raman scattering-active single Ag nanoaggregates.

We observed a background luminescence emission that was associated with surface-enhanced resonance Raman scattering (SERRS) of rhodamine 6G (R6G) molecules adsorbed on single Ag nanoaggregates and investigated the origin of the background luminescence. Thanks to the observation of single nanoaggregates, we clearly identified nanoaggregate-by-nanoaggregate variations in the steady-state and time-resolved background luminescence spectra of each nanoaggregate. From the variations in the steady-state spectra, two kinds of key properties were revealed. First, the background luminescence spectra were divided into four components: one fluorescence band corresponding to the monomers of R6G and three Lorentzian bands whose maxima were red-shifted from the fluorescence maximum of the monomer by several tens of nanometers. On the basis of the red-shifted luminescence maxima, and experimental and theoretical studies of background luminescence, we attributed the three background luminescences to fluorescence from aggregates (dimer and two kinds of higher-order aggregates) of R6G molecules on an Ag surface. Second, a positive correlation was observed between wavelengths of background luminescence maxima and wavelengths of plasmon resonance maxima. This positive correlation invoked the idea that the dipoles of both the background luminescence and the plasmon radiation are coupled with each other. From the key observations in the steady-state background luminescence spectra, we propose that two factors contribute to the variations in the steady-state background luminescence spectra; one is the aggregation (monomer, dimer, and two kinds of higher-order aggregates) of R6G molecules on an Ag surface, and the other is plasmon resonance maxima of single Ag nanoaggregates. Considering these two factors, we propose that the variations in the time-resolved background luminescence spectra are associated with deaggregation of R6G molecules (higher- to lower-order aggregates) and temporal shifts in the plasmon resonance maxima of single Ag nanoaggregates.

Image Processing, Computer-Assisted↗
PubMed2006

Elucidation of interaction between metal-free tetraphenylporphine and surface Ag atoms through temporal fluctuation of surface-enhanced resonance Raman scattering and background-light emission.

We have observed simultaneously temporal fluctuation of surface-enhanced resonance Raman scattering (SERRS) and its background-light emission from single Ag nanoaggregates that were adsorbed with metal-free tetraphenylporphine (H(2)TPP) molecules. We found that temporally stable SERRS spectra showed clearly a SERRS band that is attributed to a stretching mode of a chemical bond between a carbon atom and a non-hydrogenated nitrogen atom (C(alpha)-N). This stretching mode was not observed in regular resonance Raman spectra which are free from surface enhancement. On the other hand, we also found that temporally unstable SERRS spectra did not clearly show a C(alpha)-N stretching mode in SERRS bands. Furthermore, temporally stable SERRS spectra were accompanied by temporally stable background-light emission. Kobayashi et al. [J. Phys. Chem. 1985, 89, 5174] reported that formation of an Ag-N bond between surface Ag atoms and non-hydrogenated N atoms in a pyrrole ring enhances the intensity of a C(alpha)-N stretching mode. Thus, the observed relationship between clear appearance of a C(alpha)-N stretching mode and temporal stability of SERRS plus background-light emission strongly suggests that formation of a stable Ag-N bond suppresses fluctuation of both SERRS and background-light emission. Furthermore, the observed relationship implies that chemical contribution to SERRS is stabilization of H(2)TPP molecules that are adsorbed on SERRS-active sites by formation of Ag-N bonds. Additionally, we attributed background-light emission to luminescence of complexes between H(2)TPP molecules and surface Ag atoms considering possible formation of Ag-N bonds, synchronized SERRS intensity with background-light emission intensity, blue-shifted background-light emission maxima from normal fluorescence maxima, and previous reports related to electronic structures of H(2)TPP molecules on Ag surfaces.

Journal Article↗
PubMed2006

Surface-enhanced resonance Raman scattering and background light emission coupled with plasmon of single Ag nanoaggregates.

We investigated the optical properties of isolated single aggregates of Ag nanoparticles (Ag nanoaggregates) on which rhodamine 6G molecules were adsorbed to reveal experimentally a correlation among plasmon resonance Rayleigh scattering, surface-enhanced resonance Raman scattering (SERRS), and its background light emission. From the lack of excitation-laser energy dependence of background emission maxima we concluded that the background emission is luminescence, not Raman scattering. The polarization dependence of both SERRS and background emission was the same as that of the lowest-energy plasmon resonance maxima, which is associated with a longitudinal plasmon. From the common polarization dependence, we identified that the lowest-energy plasmon is coupled with both SERRS and background emission. In addition, we revealed that the lowest-energy plasmon with a higher quality factor (Q factor) yields larger SERRS and background emission intensity. Also, we identified that the Q factor dependence of the SERRS intensity was similar to that of the background emission intensity. This similarity directly supported us to demonstrate an enhancement of both SERRS and background emission by coupling with a common plasmon radiative mode.

Journal Article↗
PubMed2006

Hybrid dynamic coating with n-dodecyl beta-D-maltoside and methyl cellulose for high-performance carbohydrate analysis on poly(methyl methacrylate) chips.

Hybrid dynamic coating using n-dodecyl beta-d-maltoside (DDM) and methyl cellulose (MC) has been developed for suppression of analyte adsorption and electroosmotic flow (EOF) in a poly(methyl methacrylate) (PMMA) channel. The adsorption of APTS-labeled sugars in a PMMA channel was obviously suppressed with DDM dynamic coating; however, EOF was reduced only by a factor of approximately 25%, resulting in irreproducible separations. In contrast, both analyte adsorption and EOF in a PMMA channel were efficiently minimized with MC coating; however, concentrated MC above 0.3% was required to achieve high-performance separations, which greatly increased viscosity of the solution and caused difficulties during buffer loading and rinsing. In addition, n-dodecyltrimethylammonium chloride did not show observable effects on reducing analyte adsorption, although it has the same hydrophobic alkyl chain as DDM. These results strongly indicated that the polysaccharide moiety of surface modifiers has a specific affinity to surface charges and is crucial to achieving efficient and stable dynamic coating on the PMMA surface. Hybrid dynamic coating with 0.25% DDM and 0.03% MC was found to minimize both analyte adsorption and EOF in a PMMA channel to a negligible level, while still keeping a low viscosity of the solution. High-speed and high-throughput profiling of the N-linked glycans derived from alpha1-acid glycoprotein, fetuin, and ribonuclease B was demonstrated in both single-channel and 10-channel PMMA chips using DDM-MC hybrid coating. We propose that DDM-MC hybrid coating might be a general method for suppressing analyte adsorption and EOF in polymer MCE devices. The current MCE-based method might be a promising alternative for high-throughput screening of carbohydrate alterations in glycoproteins.

Adsorption↗
PubMed2006

Structure-property correlation of CdSe clusters using experimental results and first-principles DFT calculations.

Structures and properties of CdSe quantum dots (clusters) up to a diameter of approximately 2 nm were investigated by combining experimental absorption, photoluminescence (PL), and X-ray diffraction (XRD) spectroscopies as well as ab initio DFT calculations. These CdSe clusters were nucleated and grown from solutions containing respective cadmium and selenium precursors following the hot-injection technique that allows one to obtain size-controlled CdSe clusters having PL efficiency up to 0.5. The DFT calculations were performed at the B3LYP/Lanl2dz level and followed by time-dependent TDDFT calculations to estimate n energy singlet transitions. On the basis of the results of these experimental and theoretical studies, an approach to determine whether the proposed cluster with a mean diameter of approximately 2 nm is more physically reasonable is discussed. It was shown that the minimum nucleus of a CdSe cluster consists of (CdSe)(3) with a six-membered ring and planar structure. No PL is observed for this structure. The formation of the next stable cluster depends on whether hexadecylamine (HDA) was used for the growth of the CdSe clusters. In the absence of HDA, the second cluster was found to be (CdSe)(6) characterized by a broad PL spectrum, while in the presence of HDA, it was found to be (CdSe)(n) (where n > or = 14) with a sharp PL spectrum.

Journal Article↗
PubMed2006

Surfactant protein B gene variations and susceptibility to lung cancer in chromate workers.

BACKGROUND: Hexavalent chromium has been extensively investigated regarding its mutagenicity and carcinogenicity; however, its mechanism for initiating and enhancing the development of lung cancer is still obscure. Biomarkers of exposure, effect or susceptibility are required for risk assessment and for epidemiologic research studies especially in occupational settings. Since the surfactant protein system (SP) is very important for normal lung function and for mediating local airway conditions and in the clearance of the upper respiratory tract from the occupational and environmental dusts, we hypothesize that SP genes may represent good candidates to study susceptibility for lung cancer. METHODS: Using PCR genotyping methods with gel electrophoresis and confirmation of results with precise DNA fragment size measurement on microchip electrophoresis, we analyzed SP-B intron-4 polymorphism in 230 subjects who were classified into groups; chromate-related lung cancer, control chromate workers who had not developed lung cancer, control individuals with non chromate-related adenocarcinoma or squamous cell carcinoma of the lungs, or healthy Japanese control individuals. RESULTS: Our results indicated that the SP-B variants (deletion/insertion) were significantly overrepresented (61.3%) in the chromate-related lung cancer group than other groups (X2 = 47.6; DF = 4, P = 0.0001). There was a significant difference between the chromate lung cancer group and both of the control groups, healthy individuals and chromate workers who did not develop lung cancer, showing odds ratios (OR) with 95% confidence intervals (CI) of 21.9 (7.3-65.7) and 19.0 (3.78-95.4), respectively. Compared with 46 non chromate-related SCC of the lung, the SP-B variants were significantly overrepresented in the chromate-related SCC (18/28; 64.3%) than the non-chromate SCC (11/46; 23.9%) of the lung samples (X(2) = 10.27, P = 0.01), OR with 95% CI is 5.73 (2.05-16.01). CONCLUSION: These findings indicate a very strong association of the SP-B intron-4 variants with mechanisms that may enhance lung cancer susceptibility, especially in workers who are employed in chromate industry. Moreover, confirmation of such results may help to suggest adding the SP-B intron-4 typing to be one of the screening tests of the pre-placement medical examination to confirm that the worker has no variations of the SP-B gene before being engaged in a chromium-related industry, with the intention of providing proper medical counseling.

Carcinogens, Environmental↗
PubMed2006

Developmental expression of the SRF co-activator MAL in brain: role in regulating dendritic morphology.

The dynamic changes in dendritic morphology displayed by developing and mature neurons have stimulated interest in deciphering the signaling pathways involved. Recent studies have identified megakaryocytic acute leukemia (MAL), a serum response factor (SRF) co-activator, as a key component of a signaling pathway linking changes in the actin cytoskeleton to SRF-mediated transcription. To help define the role of this pathway in regulating dendritic morphology, we have characterized the pattern of MAL expression in the developing and adult brain, and have examined its role in regulating dendritic morphology in cultured cortical neurons. In histological studies of mouse brain, we found prominent expression of MAL in neurons in adult hippocampus and cerebral cortex. MAL immunostaining revealed localization of this protein in neuronal cell bodies and apical dendrites. During development, an increase in MAL expression occurs during the second post-natal week. Expression of dominant negative MAL constructs or MAL siRNA in cortical neurons grown in primary culture reduces the number of dendritic processes and decreases the basal level of SRF-mediated transcription. Taken together, these findings indicate that the MAL-SRF signaling pathway plays a key role in regulating dendritic morphology.

Animals↗
PubMed2006

Self-surface passivation of CdX (X = Se, Te) quantum dots.

A small portion of a reaction mixture including unpurified CdX (X = Se or Te) quantum dots (QDs), in which unreacted Cd and Se ions were left together with coordinating solvents, was dropped into an organic solvent. The CdX QDs in this organic solution showed enhancement of photoluminescence (PL) efficiency, growth of particles, and focusing of size distribution for more than 10 h at room temperature (RT, -23 degrees C). These effects were attributed to passivation of QDs' surface by Cd and X ions present in the solution. No external energy source was used for these achievements; therefore, the process is termed as self-surface passivation. The self-surface passivation was reproduced using purified CdX QDs with additional Cd and X ions in an organic solvent. The self-surface passivation method was applied to RT-synthesized CdSe QDs, which is characterized by a broad PL spectrum (fwhm - 150 nm) for monodispersed QDs, to modify their emission characteristics. On self-surface passivation, the broad PL spectrum was narrowed (fwhm - 35 nm) and the QDs were grown. The X-ray diffraction measurements of RT-synthesized CdSe QDs and that subsequently aged in 1-butanol showed that crystallinity of the samples was improved on aging.

Cadmium Compounds↗
PubMed2005

Rapid analysis of oligosaccharides derived from glycoproteins by microchip electrophoresis.

A novel method for fast profiling of complex oligosaccharides released from glycoproteins based on microchip electrophoresis (mu-CE) is presented here. The characterization of separation conditions, i.e., the composition, concentration and pH of running buffer as well as the applied voltage, has been performed using maltose (G2), cellobiose ( G2'), maltriose (G3) and panose (G3') as oligosaccharide isomer models. In mu-CE, much better separation of oligosaccharide isomers and oligosaccharide ladder was obtained in phosphate buffer than in borate buffer over a wide pH range. Under optimal conditions, high-performance separation of the N-linked complex oligosaccharides released from ribonuclease B, fetuin, alpha1-acid glycoprotein (AGP) and IgG was achieved using polymethylmethacrylate (PMMA) microchips with an effective separation channel of 30 mm. These results represent the first reported analysis of the N-linked oligosaccharides derived from glycoproteins by mu-CE, indicating that the present mu-CE-based method is a promising alternative for characterization of the N-linked oligosaccharides in glycoproteins.

Carbohydrate Sequence↗
PubMed2005

Subsecond luminescence intensity fluctuations of single CdSe quantum dots.

Photoluminescence (PL) intermittency characteristics are examined for single quantum dots (QDs) in a CdSe QD sample synthesized at a slow rate at 75 degrees C. Although the PL quantum efficiency was relatively low ( approximately 0.25), we noticed that the PL intensity of single CdSe QDs fluctuated on a subsecond time scale with short-lived "on" and "off" states. The subsecond PL intensity fluctuations of CdSe QDs are different from "on" and "off" PL blinking generally observed for QDs fluctuating on a millisecond to minute time scale. We characterized single QDs by identifying polarized excitations, topographic imaging using atomic force microscopy (AFM), and transmission electron microscopy (TEM). From analysis of the PL intensity trajectories from >100 single CdSe QDs, the average intermittency time was 213 ms. From the PL quantum efficiency, slow growth of QDs, intensity trajectory analyses, and previous reports relating surface trap states and PL properties of QDs, we attribute the subsecond PL intensity fluctuations of single CdSe QDs and short-lived "on" and "off" states to a high-density distribution of homogeneous surface trap states.

Cadmium Compounds↗
PubMed2005

Temperature-sensitive photoluminescence of CdSe quantum dot clusters.

The formation of narrow size dispersed and nanometer size aggregates (clusters) of cadmium selenide (CdSe) quantum dots (QDs) and their temperature-sensitive photoluminescence (PL) spectral properties close to room temperature (298 K) are discussed. CdSe QDs formed stable clusters with an average diameter of approximately 27 nm in the absence of coordinating solvents. Using transmission electron microscopy (TEM) imaging, we identified the association of individual QDs with 2-5 nm diameters into clusters of uniform size. A suspension of these clusters in different solvents exhibited reversible PL intensity changes and PL spectral shifts which were correlated with temperature. Although the PL intensity of CdSe QDs encapsulated in host matrixes and the solid state showed a response to temperature under cryogenic conditions, the current work identified for the first time QD clusters showing temperature-sensitive PL intensity variations and spectral shifts at moderate temperatures above room temperature. Temperature-sensitive reversible PL changes of clusters are discussed with respect to reversible thermal trapping of electrons at inter-QD interfaces and dipole-dipole interactions in clusters. Reversible luminescence intensity variations and spectral shifts of QD clusters show the potential for developing sensors based on QD nanoscale assemblies.

Cadmium Compounds↗
PubMed2005

High-performance genetic analysis on microfabricated capillary array electrophoresis plastic chips fabricated by injection molding.

We have developed a novel technique for mass production of microfabricated capillary array electrophoresis (mu-CAE) plastic chips for high-speed, high-throughput genetic analysis. The mu-CAE chips, containing 10 individual separation channels of 50-microm width, 50-microm depth, and a 100-microm lane-to-lane spacing at the detection region and a sacrificial channel network, were fabricated on a poly(methyl methacrylate) substrate by injection molding and then bonded manually using a pressure-sensitive sealing tape within several seconds at room temperature. The conditions for injection molding and bonding were carefully characterized to yield mu-CAE chips with well-defined channel and injection structures. A CCD camera equipped with an image intensifier was used to monitor simultaneously the separation in a 10-channel array with laser-induced fluorescence detection. High-performance electrophoretic separations of phiX174 HaeIII DNA restriction fragments and PCR products related to the human beta-globin gene and SP-B gene (the surfactant protein B) have been demonstrated on mu-CAE plastic chips using a methylcellulose sieving matrix in individual channels. The current work demonstrated greatly simplified the fabrication process as well as a detection scheme for mu-CAE chips and will bring the low-cost mass production and application of mu-CAE plastic chips for genetic analysis.

Chemistry Techniques, Analytical↗
PubMed2005

Nonradioactive telomerase activity assay by microchip electrophoresis: privileges to the classical gel electrophoresis assay.

The present study accents on the privileges of microchip-based electrophoresis to the conventional gel electrophoresis in separation of telomerase repeat amplification protocol/polymerase chain reaction (PCR) ladder products obtained in telomerase-catalyzed reaction in cancer cells. We try to clarify the interpretation of the results obtained by both electrophoretic procedures and to avoid misinterpretation as a result of PCR-dependent artefacts.

Electrophoresis, Microchip↗
PubMed2005

Role of free cadmium and selenium ions in the potential mechanism for the enhancement of photoluminescence of CdSe quantum dots under ultraviolet irradiation.

The present study describes an enhancement of the photoluminescence of CdSe quantum dots under long-term ultraviolet irradiation in organic solvents. The photoenhancement effect followed multiexponential kinetics and was found to depend on several factors: intensity of ultraviolet light, polarity of the solvent, presence of capping agents on the nanocrystal surface, and presence of free Cd and Se ions in the solution. High intensity ultraviolet irradiation provoked a rapid enhancement of the photoluminescence of CdSe nanocrystals, reaching the maximum with subsequent photoluminescence decay. Low-intensity ultraviolet irradiation provoked a comparatively slow enhancement of the photoluminescence of CdSe nanocrystals, reaching saturation after 5-6 hours of irradiation in organic solvents (butanol and chloroform). The photoenhancement effect was reversible or irreversible depending on the additional ingredients. The role of free Cd and Se in these processes was clarified. The results are discussed in the context of ultraviolet induced liberation of free Cd and Se ions from the nanocrystal surface and their hypothetical reversible deposition with trapping of the surface holes and influencing the efficiency of radiative versus nonradiative exciton decay during the enhancement of photoluminescence.

Cadmium↗