Yoshihumi Kusumoto

A spectrofluorimetric method for determining the association constants of pyrene with cyclodextrins based on polarity variation

Abstract The association constants of pyrene inclusion complexes with β-cyclodextrin and methylated β-cyclodextrins were determined using equations which provide an accurate description of the variation in the vibronic-band-intensity ratio of pyrene monomer fluorescence in the presence of cyclodextrins.

Energy transfer between rhodamine-6G and 3,3′-diethylthiacarbocyanine iodide enhanced in the premicellar region

Abstract The energy transfer between rhodamine-6G and 3,3′-diethylthiacarbocyanine iodide was studied in aqueous solutions of sodium lauryl sulfate. A highly enhanced energy transfer was observed at very low dye concentrations in the premicellar region. This effect can be explained in terms of the formation of dye-rich mixed micelles.

Absorption and fluorescence studies of the interaction of pyrene with β-cyclodextrin in aqueous surfactant solutions

Abstract The system pyrene-cyclodextrin-sodium dodecyl sulfate (SDS) in aqueous solution was studied as a function of the concentration of SDS. The behavior of absorption and fluorescence spectra of pyrene is explained in terms of complex formation with β-cyclodextrin and SDS below the critical micelle concentration and the formation of mixed micelles containing α- or β-cyclodextrin above it.

Energy transfer dye laser: Confirmation of energy transfer by reabsorption effect

Abstract The laser and fluorescence behavior was studied for the mixed dye system containing various concentrations of 3,3′-diethylthiacarbocyanine iodide and rhodamine 6G. A new way of confirming the occurrence of energy transfer is presented on the basis of the reabsorption effect.

Au-ultrathin functionalized core–shell (Fe3O4@Au) monodispersed nanocubes for a combination of magnetic/plasmonic photothermal cancer cell killing

Magnetic nanocubes, with a controlled precursor molar concentration of ferric nitrate fixed at 0.004 M to ferrous chloride ranging from 0.002 to 0.01 M, were synthesized by a new simple colloidal method at 60 °C under 1 M alkaline condition. The metallic Au-ultrathin layer was successfully functionalized on the magnetic nanocubes surface for the fabrication of the core–shell structure (Fe3O4@Au) by the borohydrate reduction of HAuCl4 in water/poly-L-histidine solution. The functionalized core–shell structure with varying molar-ratios of Fe3+/Fe2+ in aqueous media, core–shell structural characteristics (for example, size, morphology, and shell thickness), and physical properties (for example, crystalline, electronic, optical, and magnetic ones) of the resultant functional nanocubes were systematically investigated using UV-visible spectroscopy, SEM, TEM, XRD, XPS, EDX, and superconducting quantum interface device (SQUID) magnetometer analysis. The core–shell structure of Fe3O4@Au exhibits plasmonic properties with high magnetization and showed excellent hyperthermia-photothemal activity towards the cancer cell (HeLa) killing. For the hyperthermia killing of cancer cells under the alternating current magnetic field (AMF), the as-prepared Fe3O4 exhibited higher activity than the Fe3O4@Au nanoparticles. Interestingly, under the simultaneously combined AMF and photoirradiation with Fe3O4@Au, much higher cancer cell killing was found than with only AMF induced hyperthermia killing. The promoting effect of an Au-ultrathin shell supported on Fe3O4 showed strong absorption in the visible region due to localized surface plasmon resonance and increased the hyperthermia-photothermal temperature with the photothermal stability of the Fe3O4@Au nanoparticles, rather than only Fe3O4. It was found that the cell killing activity depends on the optical and magnetic properties of the Fe3O4@Au nanocubes. The optical and magnetic properties depended on the molar-concentration ratios of precursors of Fe(NO3)3·9H2O and FeCl2·4H2O. The synthesized Fe3O4@Au nanocubes have great potential for a combination of cancer imaging and local treatment as a cancer cell killing paradigm of “see and treat” applications.

Enhanced photocatalytic cytotoxic activity of Ag@Fe-doped TiO2 nanocomposites against human epithelial carcinoma cells

Fe-doped TiO2 nanopowders with controlled molar-atomic ratios of iron to titanium oxide (in percentage) ranging from nominal 1 to 10% were synthesized by a new simple sol–gel method. Metallic Ag nanoparticles were successfully deposited on the nanopowder of the Fe-doped TiO2 surface by citrate reduction of AgNO3 in water/CH3CN mixture. The molar ratio of iron to TiO2, phase formation, bandgaps, crystallinity, catalytic and plasmonic properties of the resultant composites were systematically investigated using UV-visible spectroscopy, SEM, TEM, XRD, XPS, EDX, and photoluminescence spectral analyses. The photocatalytic activity of Ag@Fe-doped TiO2 composite nanoclusters was evaluated through photocatalytic killing of cancer cells. For the photocatalytic killing of cancer cells under visible light irradiation, as-prepared Ag@Fe-doped TiO2 nanopowders exhibited higher activity than Fe-doped TiO2. The promoting effect of the Ag nanoparticles deposited on the Fe-doped TiO2 surface showed strong absorption in the visible region due to localized surface plasmon resonance of Ag and inhibited the recombination of photoelectrons and holes rather than only Fe-doped TiO2. The cytotoxic cell killing efficiency depends on the molar ratio of Fe content to TiO2. The optimum Fe content in Fe-doped TiO2 was determined to be 5% due to the Fe/TiO2 molar ratio. Based on the obtained results, a plausible mechanism was also proposed.

Synergistic enhanced photocatalytic and photothermal activity of Au@TiO2 nanopellets against human epithelial carcinoma cells

The photocatalytic and plasmonic photothermal cancer cell-killing activity of the metallic Au-capped TiO(2) (Au@TiO(2)) composite colloidal nanopellets has been investigated on HeLa cells under UV-visible (350-600 nm) light irradiation. The Au@TiO(2) composite nanopellets with the uniform Au-capped TiO(2) structure were successfully synthesized by simple reduction of HAuCl(4) on the surface of TiO(2) nanoparticles. The morphological structure and surface properties of Au@TiO(2) were characterized by using UV-visible absorption spectroscopy, TEM, SEM, XPS, EDX and XRD analyses. The formation of hydroxyl radicals (˙OH) was confirmed by photoluminescence (PL) spectra. The photocatalytic and photothermal cell-killing activity of the Au@TiO(2) nanopellets was found to vary with the molar ratio of Au to TiO(2). The direct involvement of the metal particles in mediating the electron transfer from the photoexcited TiO(2) under the band gap excitation is considered to carry out the efficient photocatalytic reaction on the cells. The plasmonic absorption spectra of Au@TiO(2) suspensions were also measured for the evaluation of photothermal cell killing. The charge separation, the interfacial charge-transfer and photothermal activity promoted the photocatalytic-photothermal cancer-cell killing more than TiO(2) alone. The cytotoxic effect of Au@TiO(2) nanopellets with low concentration of gold (TiO(2) : Au molar ratio > 1 : 1) was found to be 100%, whereas that of the commercial TiO(2) (P25) was ca. 50%. The comparative study of the cell viability using Au alone and TiO(2) alone revealed that the synergistic effect of photocatalytic hydroxyl radical formation and Au-plasmonic photothermal heat generation plays a vital role in the cancer cell killing. A plausible mechanism was also proposed for photocatalytic cancer cell killing based on the obtained results.

A comparative study on heat dissipation, morphological and magnetic properties of hyperthermia suitable nanoparticles prepared by co-precipitation and hydrothermal methods

Magnetite (Fe3O4) nanoparticles were prepared by co-precipitation and hydrothermal methods and their phase transfer was done successfully to compare their performances in different aspects. Synthesized nanoparticles were characterized for XRD, FE–SEM, TEM, UV-Vis absorption (reflectance) spectra, magnetic hysteresis loops and a.c. magnetic field induced hyperthermia. The magnetic nanoparticles prepared by the co-precipitation method show superior performances in respect of heat dissipation capability, saturation of magnetization values and particle size when compared to those prepared by the hydrothermal method.

The role of He in enhancing the intensity and lifetime of H and D emissions from laser-induced atmospheric-pressure plasma

A series of measurements have been performed on the time dependences of the intensities of helium, hydrogen, and deuterium emission lines from the corresponding laser-induced helium plasma at atmospheric pressure for two different He flow rates. The prolonged Hα and Hβ emissions along with their constant intensity ratio over a relatively extended period indicate the need to provide an alternative excitation mechanism other than the well-known thermal excitation process in a hot plasma. This additional excitation mechanism is also related to the metastable excited state of a He atom as indicated by the similar characteristics of the observed time dependence of the emission intensities. The enhanced intensity and lifetime of He emission at a high He flow rate was explained in terms of the collision-induced increase in the number of He atoms excited to above the 2 S10 metastable state, which was also responsible for the delayed excitation of H and D atoms via an energy transfer mechanism involving a Penning-...

Detection of deuterium and hydrogen using laser-induced helium gas plasma at atmospheric pressure

An experimental study on gas analysis by means of laser-induced breakdown spectroscopy was conducted using a Nd-yttrium aluminum garnet laser (1,064 nm, 120 mJ, 8 ns) and helium host gas at atmospheric pressure on a sample of mixed water (H2O) and heavy water (D2O) in vapor form. It was shown that completely resolved hydrogen (Hα) and deuterium (Dα) emission lines that are separated by only 0.179 nm could be obtained at a properly delayed detection time when the charged particles responsible for the strong Stark broadening effect in the plasma have mostly disappeared. It is argued that the helium metastable excited state plays an important role in the hydrogen excitation process.