Atmospheric gas plasma–induced ROS production activates TNF-ASK1 pathway for the induction of melanoma cancer cell apoptosis

Atmospheric gas plasmas (AGPs) are able to selectively induce apoptosis in cancer cells, offering a promising alternative to conventional therapies that have unwanted side effects such as drug resistance and toxicity. However, the mechanism of AGP-induced cancer cell death is unknown. In this study, AGP is shown to up-regulate intracellular reactive oxygen species (ROS) levels and induce apoptosis in melanoma but not normal melanocyte cells. By screening genes involved in apoptosis, we identify tumor necrosis factor (TNF)-family members as the most differentially expressed cellular genes upon AGP treatment of melanoma cells. TNF receptor 1 (TNFR1) antagonist-neutralizing antibody specifically inhibits AGP-induced apoptosis signal, regulating apoptosis signal-regulating kinase 1 (ASK1) activity and subsequent ASK1-dependent apoptosis. Treatment of cells with intracellular ROS scavenger N-acetyl-l-cysteine also inhibits AGP-induced activation of ASK1, as well as apoptosis. Moreover, depletion of intracellular ASK1 reduces the level of AGP-induced oxidative stress and apoptosis. The evidence for TNF-signaling dependence of ASK1-mediated apoptosis suggests possible mechanisms for AGP activation and regulation of apoptosis-signaling pathways in tumor cells.

Nanoparticles in cancer imaging and therapy

Nanoparticle contrast agents offer the potential to significantly improve existing methods of cancer diagnosis and treatment. Advantages include biocompatibility, selective accumulation in tumor cells, and reduced toxicity. Considerable research is underway into the use of nanoparticles as enhancement agents for radiation therapy and photodynamic therapy, where they may be used to deliver treatment agents, produce localized enhancements in radiation dose and selectively target tumor cells for localized damage. This paper reviews the current status of nanoparticles for cancer treatment and presents preliminary results of a pilot study investigating titanium dioxide nanoparticles for dual-mode enhancement of computed tomography (CT) imaging and kilovoltage radiation therapy. Although titanium dioxide produced noticeable image contrast enhancement in the CT scans, more sensitive detectors are needed to determine whether the nanoparticles can also produce localized dose enhancement for targeted radiation therapy.

Uniformity of postprocessing of dense nanotube arrays by neutral and ion fluxes

The advantages of using low-temperature plasma environments for postprocessing of dense nanotube arrays are shown by means of multiscale hybrid numerical simulations. By controlling plasma-extracted ion fluxes and varying the plasma and sheath parameters, one can selectively coat, dope, or functionalize different areas on nanotube surfaces. Conditions of uniform deposition of ion fluxes over the entire nanotube surfaces are obtained for different array densities. The plasma route enables a uniform processing of lateral nanotube surfaces in very dense (with a step-to-height ratio of 1:4) arrays, impossible via the neutral gas process wherein radical penetration into the internanotube gaps is poor. © 2006 American Institute of Physics.

Nanopore processing in dielectric materials and dielectric template-assisted nanoarray synthesis : using pulsed bias to enhance process throughput and precision

An effective technique to improve the precision and throughput of energetic ion condensation through dielectric nanoporous templates and reduce nanopore clogging by using finely tuned pulsed bias is proposed. Multiscale numerical simulations of ion deposition show the possibility of controlling the dynamic charge balance on the upper template's surface to minimize ion deposition on nanopore sidewalls and to deposit ions selectively on the substrate surface in contact with the pore opening. In this way, the shapes of nanodots in template-assisted nanoarray fabrication can be effectively controlled. The results are applicable to various processes involving porous dielectric nanomaterials and dense nanoarrays.

Diagnostics and two-dimensional simulation of low-frequency inductively coupled plasmas with neutral gas heating and electron heat fluxes

This article presents the results on the diagnostics and numerical modeling of low-frequency (∼460 KHz) inductively coupled plasmas generated in a cylindrical metal chamber by an external flat spiral coil. Experimental data on the electron number densities and temperatures, electron energy distribution functions, and optical emission intensities of the abundant plasma species in low/intermediate pressure argon discharges are included. The spatial profiles of the plasma density, electron temperature, and excited argon species are computed, for different rf powers and working gas pressures, using the two-dimensional fluid approach. The model allows one to achieve a reasonable agreement between the computed and experimental data. The effect of the neutral gas temperature on the plasma parameters is also investigated. It is shown that neutral gas heating (at rf powers≥0.55kW) is one of the key factors that control the electron number density and temperature. The dependence of the average rf power loss, per electron-ion pair created, on the working gas pressure shows that the electron heat flux to the walls appears to be a critical factor in the total power loss in the discharge.

Equilibrium and relaxation of particulate charge in fluorocarbon plasmas

Charging of micron-size particulates, often appearing in fluorocarbon plasma etching experiments, is considered. It is shown that in inductively coupled and microwave slot-excited plasmas of C4F8 and Ar gas mixtures, the equilibrium particle charge and charge relaxation processes are controlled by a combination of microscopic electron, atomic (Ar+ and F+), and molecular ion (CF+ 3, CF+ 2, and CF+) currents. The impact of molecular ion currents on the particulate charging and charge relaxation processes is analyzed. It is revealed that in low-power (<0.5 kW) microwave slot-excited plasmas, the impact of the combined molecular ion current to the total positive microscopic current on the particle can be as high as 40%. The particulate charge relaxation rate in fluorocarbon plasmas appears to exceed 108 s-1, which is almost one order of magnitude higher than that from purely argon plasmas. This can be attributed to the impact of positive currents of fluorocarbon molecular ions, as well as to the electron density fluctuations with particle charge, associated with electron capture and release by the particulates.

Standing surface waves in a dust-contaminated large-area planar plasma source

The effect of charged particulates or dusts on surface wave produced microwave discharges is studied. The frequencies of the standing electromagnetic eigenmodes of large-area flat plasmas are calculated. The dusts absorb a significant amount of the plasma electrons and can lead to a modification of the electromagnetic field structure in the discharge by shifting the originally excited operating mode out of resonance. For certain given proportions of dusts, mode conversion is found to be possible. The power loss in the discharge is also increased because of dust-specific dissipations, leading to a decrease of the operating mode quality factor.

Extremely non-equilibrium synthesis of luminescent zinc oxide nanoparticles through energetic ion condensation in a dense plasma focus device

Luminescent ZnO nanoparticles have been synthesized on silicon and quartz substrates under extremely non-equilibrium conditions of energetic ion condensation during the post-focus phase in a dense plasma focus (DPF) device. Ar+, O+, Zn+ and ZnO+ ions are generated as a result of interaction of hot and dense argon plasma focus with the surfaces of ZnO pellets placed at the anode. It is found that the sizes, structural and photoluminescence (PL) properties of the ZnO nanoparticles appear to be quite different on Si(1 0 0) and quartz substrates. The results of x-ray diffractometry and atomic force microscopy show that the ZnO nanoparticles are crystalline and range in size from 5-7 nm on Si(1 0 0) substrates to 10-38 nm on quartz substrates. Room-temperature PL studies reveal strong peaks related to excitonic bands and defects for the ZnO nanoparticles deposited on Si (1 0 0), whereas the excitonic bands are not excited in the quartz substrate case. Raman studies indicate the presence of E2 (high) mode for ZnO nanoparticles deposited on Si(1 0 0).

Bistability and hysteresis in inductively coupled plasmas

The transition between the two stable operation regimes (E and H discharge modes) in inductively coupled argon plasmas has been studied experimentally and theoretically. Analogy with other physical phenomena exhibiting hysteresis has been drawn. Analysis of power balance, electromagnetic field, plasma parameters, densities of the excited states, and optical emission spectra shows that the hysteresis may be due to nonlinearities associated with step-wise ionization through excited states of the argon atoms.

Optical emission characteristics and mode transitions in low-frequency inductively coupled plasmas

An attempt was made to investigate the optical emission spectra of atomic, molecular, and ionic species in low-frequency, high-density ICP discharges in pure nitrogen, ar con gases, and gas mixtures Ar+H2, N2+Ar, and N2+H2. The excited species were identified by in situ optical emission intensity (OEI) measurements in the discharge chamber. In general, significant results were obtained.

SiC-like phase and room-temperature photoluminescence of low-k SiOCH films

Carbon-doped hydrogenated silicon oxide (SiOCH) low-k films have been prepared using 13.56 MHz discharge in trimethylsilane (3MS) - oxygen gas mixtures at 3, 4, and 5 Torr sustained with RF power densities 1.3 - 2.6 W/cm2. The atomic structure of the SiOCH films appears to be a mixture the amorphous SiO2-like and the partially polycrystalline SiC-like phases. Results of the infra-red spectroscopy reflect the increment in the volume fraction of the SiC-like phase from 0.22 - 0.28 to 0.36 - 0.39 as the RF power increment. Steady-state near-UV laser-excited (364 nm wavelength, 40±2 mW) photoluminescence (PL) has been studied at room temperatures in the visible (1.8 eV - 3.1 eV) subrange of photon spectrum. Two main bands of the PL signal (at the photon energies of 2.5 - 2.6 eV and 2.8 - 2.9 eV) are observed. Intensities of the both bands are changed monotonically with RF power, whereas the bandwidth of ∼0.1 eV remains almost invariable. It is likely that the above lines are dumped by the non-radiative recombination involving E1-like centres in the amorphous-nanocrystalline SiC-like phases. Such explanation of the PL intensity dependences on the RF power density is supported by results of experimental studies of defect states spectrum in bandgap of the SiOCH films.

Parametric excitation of high-frequency surface waves in a plasma-metal waveguide structure

The problem concerning the excitation of high-frequency surface waves (SW) propagating across an external magnetic field at a plasma-metal interface is considered. A homogeneous electric pump field is applied in the direction transverse with respect to the plasma-metal interface. Two high-frequency SW from different frequency ranges of existence and propagating in different directions are shown to be excited in this pump field. The instability threshold pump-field values and increments are obtained for different parameters of the considered waveguide structure. The results associated with saturation of the nonlinear instability due to self-interaction effects of the excited SW are given as well. The results are appropriate for both gaseous and semiconductor plasmas.

Atmospheric-pressure plasma jets : effect of gas flow, active species, and snake-like bullet propagation

Cold atmospheric-pressure plasma jets have recently attracted enormous interest owing to numerous applications in plasma biology, health care, medicine, and nanotechnology. A dedicated study of the interaction between the upstream and downstream plasma plumes revealed that the active species (electrons, ions, excited OH, metastable Ar, and nitrogen-related species) generated by the upstream plasma plume enhance the propagation of the downstream plasma plume. At gas flows exceeding 2 l/min, the downstream plasma plume is longer than the upstream plasma plume. Detailed plasma diagnostics and discharge species analysis suggest that this effect is due to the electrons and ions that are generated by the upstream plasma and flow into the downstream plume. This in turn leads to the relatively higher electron density in the downstream plasma. Moreover, high-speed photography reveals a highly unusual behavior of the plasma bullets, which propagate in snake-like motions, very differently from the previous reports. This behavior is related to the hydrodynamic instability of the gas flow, which results in non-uniform distributions of long-lifetime active species in the discharge tube and of surface charges on the inner surface of the tube.

Comparative behavior of CdS and CdSe quantum dots in poly(3-hexylthiophene) based nanocomposites

CdS and CdSe nanoparticles have been prepared using conducting poly(3-hexylthiophene) (P3HT) matrix with an objective to understand the effect of nanoparticles on the polymer matrix using electrochemical and spectroscopic techniques. The spectroscopic results reveal that the electronic structure of polymer is strongly influenced by the characteristics of embedded semiconducting nanoparticles. SEM and TEM images show the ordered morphology of the CdS and CdSe nanoparticles in presence of the polymer matrix. Cyclic voltammetry performed both in the presence and absence of light enables us to understand the redox changes in P3HT due to CdS and CdSe quantum dots such as the generation of free radical in the excited state and their electrochemical band gaps.

Rodlike bimetallic ruthenium and osmium complexes bridged by phenylene spacers. Synthesis, electrochemistry, and photophysics

In the search for light-addressable nanosized compounds we have synthesized 10 dinuclear homometallic trisbipyridyl complexes of linear structure with the general formula [M(bpy)3-BL-M(bpy)3]4+ [M = Ru(II) or Os(II); BL = polyphenylenes (2, 3, 4, or 5 units) or indenofluorene; bpy = 2,2′-bipyridine]. By using a "chemistry on the complex" approach, different sizes of rodlike systems have been obtained with a length of 19.8 and 32.5 Å for the shortest and longest complex, respectively. For one of the ruthenium precursors, [RUbpy-ph2-Si(CH3) 3][PF6]2, single crystals were obtained by recrystallization from methanol. Their photophysical and electrochemical properties are reported. All the compounds are luminescent both at room and low temperature with long excited-state lifetimes due to an extended delocalization. Nanosecond transient absorption showed that the lowest excited state involves the chelating unit attached to the bridging ligand. Electrochemical data indicated that the first reduction is at a slightly more positive potential than for the reference complexes [M(bpy)3]2+ (M = Ru, Os). This result confirms that the best acceptor is the bipyridine moiety connected to the conjugated spacers. The role of the tilt angle between the phenylene units, in the two series of complexes, for the ground and excited states is discussed.