X. Lu

The selective effect of plasma activated medium in an in vitro co-culture of liver cancer and normal cells

In this work, a co-culture system with liver cancer cell line HepG2 and normal cell line L02 is used to investigate the selective effect on cancer and normal cells by plasma activated medium (PAM), which is closer to the real environment where cancer cells develop. Besides, the co-culture system is a better model to study the selective effect than the widely used separate culture systems, where the cancer cell line and normal cell line are cultured independently. By using the co-culture system, it is found that there is an optimum dose of PAM to induce significant cancer cell apoptosis while keeping minimum damage to normal cells.

The effect of applied electric field on pulsed radio frequency and pulsed direct current plasma jet array

Here we compare the plasma plume propagation characteristics of a 3-channel pulsed RF plasma jet array and those of the same device operated by a pulsed dc source. For the pulsed-RF jet array, numerous long life time ions and metastables accumulated in the plasma channel make the plasma plume respond quickly to applied electric field. Its structure similar as “plasma bullet” is an anode glow indeed. For the pulsed dcplasma jet array, the strong electric field in the vicinity of the tube is the reason for the growing plasma bullet in the launching period. The repulsive forces between the growing plasma bullets result in the divergence of the pulsed dcplasma jet array. Finally, the comparison of 309u2009nm and 777u2009nm emissions between these two jet arrays suggests the high chemical activity of pulsed RF plasma jet array.

OH density optimization in atmospheric-pressure plasma jet by using multiple ring electrodes

OH radical is one of the important reactive species generated by non-equilibrium atmospheric-pressure plasma jets, which is believed to play an important role in plasma medicine applications such as cancer therapy, wound healing and sterilization. In this study, a method to increase OH density is proposed. By using multiple pairs of ring electrodes, we generate 3–5 times more OH radicals than in the common device which uses only one high-voltage ring electrode. Discharge imaging shows that the plasma plume with only one ring electrode is longer and its emission intensity is higher than those with multiple pairs of ring electrodes. Further studies indicate that the distribution of OH radicals is significantly influenced by the gas flow rate. At higher gas flow rates, the OH peak concentration is detected further away from the nozzle, and the position of the peak OH concentration correlates with the product of the gas flow velocity and the pulse duration. As observed from the emission spectra, multiple electrodes only enhance the plasma inside the tube rather than the plasma plume in the surrounding air. These results suggest that the OH radicals are mainly generated inside the tube and then delivered to the outer plasma plume region by the gas flow.

A battery-operated atmospheric-pressure plasma wand for biomedical applications

Summary form only given. A handheld, battery-operated atmospheric-pressure plasma rod (named plasma wand, Fig. 1) which does not rely on external power source (e.g., wall power or power generator) and gas supply is reported1. The plasma wand can be used for killing bacteria, fungi, or viruses that are hidden in narrow channels such as nasal cavity and ear canal, which are difficult to access using most of currently available devices. Besides, the electrical characterization, plasma wand temperature, emission spectra of the plasma, ozone and OH radical concentration generated by the device, are investigated by different diagnostic methods. The temperature on the plasma wand stays at about 38°C after operating for about 5 minute and the outside electrode is grounded. So there is no feeling of hot or electrical shock at all when we hold the plasma wand. From the Lissajous-figure of the discharge, the power consumption is estimated to be about 12 W. The ozone concentration reaches 120 ppm at 1 mm away from the device and the OH concentration reaches 3.5×1014 cm-3 in the plasma. The preliminary bacteria inactivation experiment results show that all bacteria samples on the microfiltration membrane are killed by this device within 30 s.

On the penetration depth of reactive oxygen and nitrogen species generated by a plasma jet through real biological tissue

In this work, an actual biological tissue is used to investigate how thick the reactive oxygen and nitrogen species (RONS) produced by a plasma jet can penetrate through the tissue. This is one of the most critical questions in plasma medicine. The concentration of RONS (O3, H2O2, OH, NO2−, NO2− + NO3−) produced by the plasma jet penetrating through different thickness of the tissue is measured. It is found that the reactive oxygen species (ROS) produced by the plasma are significantly consumed by the tissue. For the tissue thickness of 500u2009μm, there is only about five percent or even less of the ROS (O3, H2O2, and OH) penetrating through the tissue. On the other hand, more than 80% of the reactive nitrogen species (NO2− + NO3−) are able to penetrate through the 500u2009μm biological tissue. Furthermore, under certain experimental conditions, some of the RONS can penetrate through 1.25u2009mm of the biological tissue. Finally, besides H2O2, NO2−, and NO3−, there is some other unknown RONS that penetrate through t...

The effect of three different methods of adding O2 additive on O concentration of atmospheric pressure plasma jets (APPJs)

In order to maximize the O concentration generated by the atmospheric pressure plasma jets (APPJs), several different methods of adding O2 additive to working gas have been proposed. However, it is not clear, which method is capable of generating the highest concentration of O atom. In this paper, the concentration of O atoms in an APPJs by adding O2 to (1) the working gas, to (2) the downstream inside the tube, and (3) to the shielding gas is investigated by two-photon absorption laser-induced fluorescence spectrometry. The results clearly demonstrate that the highest O density is achieved when 1.5% of O2 is added to the working gas rather than the other two methods. In other words, the most effective way to generate O atoms is by premixing O2 with the working gas. Further investigation suggests that O atoms are mainly generated around the electrode region, where the electric field is highest. In addition, when O2 is added to the working gas, if in the meantime extra O2 is added to the downstream inside ...

The effect of seed electrons on the repeatability of atmospheric pressure plasma plume propagation: I. Experiment

One of the significant differences between the traditional streamers and the plasma jets is the repeatability of their propagation. In this paper, the effect of the seed electron density on the repeatability of the plasma jets is investigated. The seed electron density plays an essential role in the propagation of plasma plume which is in either repeatable mode or random mode depending on the frequency of the applied voltage and the mixture percentage of the working gas. By measuring the propagation velocities and the ignition delay time, it is found that the propagation velocities of the plasma plume are independent of the seed electron density. However, the jitter of the ignition delay time strongly depends on the frequency of the applied voltage and the mixture percentage of the working gas. After detailed analyzing of the experiment results, it is concluded that the minimum seed electron density required for the plasma bullet to propagate in repeatable mode is on the order of 108 cm−3 for gas pressure...

Medical applications of nonthermal atmospheric pressure plasma in dermatology: Applications of nonthermal plasma in cutaneous diseases

Plasma is an ionized gas that consists of positively and negatively charged particles, neutral atoms, and photons. Recent developments in plasma sources have made it possible to generate room‐temperature plasma in the “open air”, thus enabling the application of plasma in vivo. Using nonthermal plasma, active agents can be efficiently delivered to target cells without creating thermal damage. Also known as cold atmospheric pressure plasma (CAP), nonthermal atmospheric pressure plasma offers innovative medical applications. In this context, it has also gained wide attention in the field of dermatology. The complex and variable mixture of active agents in plasma – predominantly reactive oxygen and nitrogen species (ROS, RNS) – can control or trigger complex biochemical reactions, achieving the desired effects in a dose‐dependent manner. The objective of the present review is to present potential applications of plasma in dermatology and analyze its potential mechanisms of action.

Active species delivered by dielectric barrier discharge filaments to bacteria biofilms on the surface of apple

The atmospheric pressure non-equilibrium plasma has shown a significant potential as a novel food decontamination technology. In this paper, we report a computational study of the intersection of negative streamer produced by air dielectric barrier discharge with bacteria biofilm on an apple surface. The structure, conductivities, and permittivities of bacteria biofilm have been considered in the Poissons equations and transportation equations of charge and neutral species to realize self-consistent transportation of plasma between electrode and charging surfaces of apple. We find that the ionization near the biofilm facilitates the propagation of negative streamer when the streamer head is 1u2009mm from the biofilm. The structure of the biofilm results in the non-uniform distribution of ROS and RNS captured by flux and time fluence of these reactive species. The mean free path of charged species in μm scale permitted the plasma penetrate into the cavity of the biofilm, therefore, although the density of ROS...

Visible light effects in plasma plume ignition

The breakdown delay time of a closed plasma plume excited by a high-voltage pulse is investigated. The visible monochromatic light of 404, 532, and 662u2009nm wavelength and narrow-waveband light at a central wavelength of 400, 430, 450, 470, 500, 530, 570, 610, and 630u2009nm are used to pre-ionize the gas. It is found that the breakdown delay time decreases when the visible light illuminates the discharge tube. The light is most effective when it is applied at the position near the high-voltage electrode. Besides, the tube material and size are important for enhancing the effect. The jet using quartz tube and larger inner diameter make the effect stronger. The effect of visible light is found to inversely relate to the wavelength, manifested by the longer breakdown delay times for longer wavelengths. With increasing the frequency and the pulse width of the voltage, the visible light shortens the delay time more effectively. These observations can be explained by the visible light-enhanced generation of free electrons before the ignition. The proposed mechanisms of free-electron generation are the optically stimulated exoelectron emission from the inner surface of the discharge tube wall and the vibrational excitation of nitrogen molecules. The effects of visible light weaken with the addition of oxygen as a result of electron affinity to oxygen.