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.

Are dopant-stabilized visible light-responsive photocatalysts efficient and stable?

Nitrogen and carbon codopants-stabilized hierarchical porous ZnS microspheres undergo an unexpected dynamic transformation into hollow microspheres when nitrogen and carbon are removed from the former. Thus, such a transformation is evidence for the unprecedented stability of non-metal doped visible light-responsive photocatalysts.

Plasmon-induced photothermal cell-killing effect of gold colloidal nanoparticles on epithelial carcinoma cells.

Gold colloidal nanoparticles were prepared by the liquid laser ablation of a gold metal plate in water and also by the citrate reduction of HAuCl(4).4H2O. The gold colloidal nanoparticles with the plasmonic band strongly absorb light, which is converted to the photothermal energy. This photothermal energy gives a cytotoxic effect on epithelial carcinoma cells. Interestingly, we found that the size and shape of the nanoparticles are changed by light during the photothermal process in vitro. The cervical carcinoma cell line (HeLa cell) was incubated with the colloidal gold nanoparticles and then exposed to continuous visible light at 400-600 nm with UV- and heat-cutoff filters. The distinct cell-killing effect was observed by this procedure. In the absence of the gold colloidal nanoparticles, only a small amount of cells were photothermally destroyed.

Photophysical and photochemical studies of chlorophyll a and cobalt(II)tetraphenylporphyrin in poly(L-glutamate)-decylammonium ion complex.

Spectroscopic studies were carried out on chlorophyll a and cobalt(II)tetraphenylporphyrin solubilized in a poly(L-glutamate) (Poly(Glu))-decylammonium chloride (DeAC) complex system, in the presence of methylviologen (MV2+). The cooperative binding occurred between the anionic Poly(Glu) and the cationic DeAC, leading to the formation of micelle-like hydrophobic clusters of DeAC and also the change in conformation of the Poly(Glu) from the random coil to the alpha-helix. All of the absorption spectra, the fluorescence quantum yields and the fluorescence lifetimes indicated the existence of equilibrium between the aggregated biofunctional molecules in the bulk phase and the monomeric species in the complex phase of the Poly(Glu)-DeAC solution. The fluorescence quenching of the biofunctional molecules by methylviologen indicates that the conformation-dependent electron transfer occurs in the complex phase.

Visible-light induced hydrogen production using a polypeptide-chlorophyll complex with alpha-helix conformation.

Hydrogen production was accomplished under visible-light irradiation by using a system consisting of a biomolecule (chlorophyll a), methylviologen, ethylenediaminetetraacetic acid disodium salt and Pt-loaded poly(l-glutamate) (Poly(Glu)), in aqueous decylammonium chloride (DeAC) solution. Spectroscopic studies revealed that chlorophyll a is solubilized in the hydrophobic clusters of Pt-loaded Poly(Glu)-decylammonium chloride. In the Poly(Glu)-DeAC complex, the electron transfer occurred between chlorophyll a and methylviologen leading to hydrogen production. The most noticeable result is that the rate of hydrogen evolution depends on the change from the random coil to the alpha-helix in conformation of Poly(Glu) induced by the cooperative binding with DeAC.

Quantitative analysis of deuterium using laser-induced plasma at low pressure of helium.

It was proved that the analysis of deuterium can be conducted using laser-induced plasma spectroscopy. By selecting the appropriate surrounding gas, its pressure, and gating time of the detection system, it was shown that the emission lines of both hydrogen (H(alpha)) and deuterium (D(alpha)), separated by only 0.179 nm, can be fully resolved. A linear calibration curve was also obtained, indicating that this technique has the potential for quantitative analysis of deuterium. The minimum detection limit achieved in this stage of research was estimated to be 50 ppm. We have also shown that this technique can be used as a simple and rapid method for D and H analysis in solid samples.

Potentiometric and Spectroscopic Characterization of Copolypeptide-Surfactant Complexes Formed by a Cooperative Binding System.

The binding behavior of an anionic surfactant, sodium dodecyl sulfate (SDS), to a series of L-lysine-containing copolypeptides in aqueous solutions was investigated in relation to the conformational change of copolypeptide-surfactant complexes with the use of potentiometric and spectroscopic techniques. The present results of CD spectra and the binding isotherm of SDS by copolypeptides of opposite charges can lead us to conclude that SDS binds cooperatively to the positively charged side groups of a series of copolypeptides used in this work, resulting in the formation of a micelle-like cluster due to an additional hydrophobic interaction among bound SDS ions. Solid-state properties of the stoichiometric copolypeptide-SDS complexes were also examined by using CD and FT-IR spectroscopies; (Lys, Tyr) (1:1) and (4:1) systems adopt a beta-pleated sheet conformation, while (Lys, Trp) (4:1) and (Lys, Phe) (1:1) systems adopt an alpha-helical conformation. Based on the results of FT-IR spectra, in all cases surfactant alkyl chains of SDS in the solid complexes were in an extended conformation. Copyright 2000 Academic Press.