Weidong Xia

Effects and Mechanism of Atmospheric-Pressure Dielectric Barrier Discharge Cold Plasma on Lactate Dehydrogenase (LDH) Enzyme

Proteins are carriers of biological functions and the effects of atmospheric-pressure non-thermal plasmas on proteins are important to applications such as sterilization and plasma-induced apoptosis of cancer cells. Herein, we report our detailed investigation of the effects of helium-oxygen non-thermal dielectric barrier discharge (DBD) plasmas on the inactivation of lactate dehydrogenase (LDH) enzyme solutions. Circular dichroism (CD) and dynamic light scattering (DLS) indicate that the loss of activity stems from plasma-induced modification of the secondary molecular structure as well as polymerization of the peptide chains. Raising the treatment intensity leads to a reduced alpha-helix content, increase in the percentage of the beta-sheet regions and random sequence, as well as gradually decreasing LDH activity. However, the structure of the LDH plasma-treated for 300 seconds exhibits a recovery trend after storage for 24 h and its activity also increases slightly. By comparing direct and indirect plasma treatments, plasma-induced LDH inactivation can be attributed to reactive species (RS) in the plasma, especially ones with a long lifetime including hydrogen peroxide, ozone, and nitrate ion which play the major role in the alteration of the macromolecular structure and molecular diameter in lieu of heat, UV radiation, and charged particles.

Genetic effects of an air discharge plasma on Staphylococcus aureus at the gene transcription level

The dynamics of gene expression regulation (at transcription level) in Staphylococcus aureus after different doses of atmospheric-pressure room-temperature air plasma treatments are investigated by monitoring the quantitative real-time polymerase chain reaction. The plasma treatment influences the transcription of genes which are associated with several important bio-molecular processes related to the environmental stress resistance of the bacteria, including oxidative stress response, biofilm formation, antibiotics resistance, and DNA damage protection/repair. The reactive species generated by the plasma discharge in the gas phase and/or induced in the liquid phase may account for these gene expression changes.

Numerical Study of DC Argon Arc with Axial Magnetic Fields

Numerical simulation of an atmospheric DC arc under an axial magnetic field (AMF) is performed with a model of unifying the plasma and electrodes. In the model the configuration of the cathodic arc attachment is free. Results are given for a 200A argon arc under 0–0.02T AMF. The simulation results indicate that, with the AMF, the cathode arc attachment shrinks towards its tip. That induces many changes of arc configuration and arc parameters, different from the calculation assuming a fixed cathodic arc attachment: as the AMF increases, the plasma temperature nearby the cathode tip increases higher; the low temperature hollow of plasma nearby the anode expands more intensively in both axial and radial direction; the profile of current density on the anode exhibits a bigger concave shape; arc voltage drop increases more; and more power is delivered to the anode. The elements that cause the changes are discussed.

Observation of Thermal Cathodic Hot Spots in a Magnetically Rotating Arc Plasma Generator

At atmospheric pressure, cathodic arc root tends to shrink to a luminous hot spot, which limits arc column expanding and accelerates cathode ablative rates. To obtain a nonconstricted cathodic arc root, we built a magnetically rotating arc plasma generator that mainly consists of a cylindrical graphite anode chamber, a concentric lanthanum tungsten cathode, and a solenoid coil for producing an axial magnetic field (AMF). Evolution of self-organized multihot spots on cathode end is observed in this study. Results show that with the AMF, arc currents, or/and cathode temperature increasing, the spots quantity gradually increases, and at last multispots evolve into a diffuse annular one. When the arc column is constricted, the arc moves on the spots periodically. Thus, a single constricted cathodic root is formed. By controlling the axial gas flow, the constricted arc converts into a diffusive one which covers all spots simultaneously, and then multiroots or diffuse annular root are developed. The cathodic spots and roots formation mechanism are proposed, and experimental results support the prediction of nonlinear surface heating model.

Diffuse and spot mode of cathode arc attachments in an atmospheric magnetically rotating argon arc

Summary form only given. To understand the arc and thermal plasmas, a wide range of numerical simulations based n computational fluid dynamics coupled with electromagnetics have been carried out. Although the LTE models are proved successful to predict plasma temperature, deviations from LTE are experimentally observed, especially around the arc fringe1. Furthermore, the interaction of plasma with cathode surface plays a key role in the whole discharge processe2, 3. To research cathode discharge phenomena with a thermionic, a model including the cathode, the near-cathode layer and the arc column is needed.A typical case is the discharge processes in a atmospheric magnetically rotating argon arc4, 5. Magnetically rotating arcs have been increasingly adopted in dc arc plasma devices for diagnostics and material processing, modern circuit breakers, etc. Many issues remain unclear. One is the spontaneous switching of the dc arc with a thermionic cathode between two distinguished discharge modes: diffuse mode and spot mode. It is noted that, in our simulation the arc column is calculated simultaneously with the near-cathode region and the cathode. Comparative investigation of two modes of attachment of a dc (I=50A,100A) atmospheric pressure arc in argon to a thermionic cathode made of pure tungsten is carried out. Both experimental and computational data reveals that there exist two modes of arc discharge: the spot mode, which has a obvious cathode surface temperature peak in the arc attachment center ; the diffuse mode, which has a flat cathode surface temperature distribution and a larger arc attachment area.

Selective effects of non-thermal atmospheric plasma on triple-negative breast normal and carcinoma cells through different cell signaling pathways

Non-thermal atmospheric plasma (NTP) has shown its selective anticancer effects in many types of tumors in vitro and one of the main mechanisms is that the different increase of intracellular ROS in cancer and homologous normal cells. In this study, we report that NTP treatment reduces the proliferation in triple negative breast cancer (TNBC) and normal cell lines. Simultaneously, STAT3 pathway is inhibited by NTP effects. However, it is observed that normal cells MCF10A are more sensitive to ROS toxicity induced by NTP than cancer cells MDA-MB-231. When 5 mM of ROS inhibitor N-acetyl cysteine (NAC) is employed in NTP treatments, the proliferation of normal breast cells MCF10A recovers. Meanwhile, NTP effects remain significant inhibition of MDA-MB-231 cells. Our results further reveal that NTP can induce apoptosis in MDA-MB-231 cells through inhibiting interleukin-6 receptor (IL-6R) pathway. Moreover, the mechanism of NTP anti-cancer selectivity relates to constantly HER2/Akt activation induced by NTP especially in MCF10A cells but not in MDA-MB-231 cells. Therefore, these two different cell signaling pathways induced by NTP treatments in TNBC and homologous normal cells make NTP becoming a potential tool in future therapy.

Roles of membrane protein damage and intracellular protein damage in death of bacteria induced by atmospheric-pressure air discharge plasmas

Although plasma sterilization has attracted much attention, the underlying mechanisms and biochemical pathways are still not fully understood. In this work, we investigate the molecular mechanism pertaining to the inactivation of Escherichia coli (E. coli) by air discharge plasmas. The membrane protein YgaP and intracellular protein swc7 are over-expressed in E. coli by genetic recombination and gene inducible expression techniques and plasma exposure is demonstrated to alter the structures of YgaP and swc7 in E. coli. The plasma-induced damage of YgaP and swc7 involves changes in the secondary and tertiary structures instead of the primary structure and the modification effectiveness depends on the storage time after the plasma treatment. Owing to the unique structure of E. coli, YgaP is more susceptible to the plasma treatment than intracellular swc7. Within 1 h after plasma exposure, YgaP is modified but not swc7, but after 1 h or longer, both YgaP and swc7 proteins are indeed modified. By analyzing the plasma-induced antimicrobial efficacy and modification of YgaP and swc7, plasma-induced modification of the membrane proteins is the major cause of bacterial death but there is no identifiable relationship with modification of the intracellular protein. The new results provide insights into the mechanism of multiple plasma-induced damage to bacteria and cells as well as the disinfection mechanism.