Water in atmospheric-pressure helium rf plasmas

Radio frequency (rf) plasmas operated at atmospheric pressure have received great attention in recent years for their potential use in many scientific and industrial applications. The optical emission profile of these atmospheric pressure rf discharges typically presents two bright layers, one above each of the electrodes. Although in the low-pressure regime bright layers near the electrodes are typically associated with the so-called gamma mode, these layers are observed in the alpha mode at atmospheric pressure and only after a significant increase in current, the transition into the gamma mode takes place. In the gamma mode, the bright layers are found to light up in an alternating fashion, corresponding to the excitation of radiative states by avalanches across the sheaths. On the other hand, in the alpha mode, the bright layers light up simultaneously mostly as a result of the acceleration of bulk electrons in the expanding and retreating sheathbulk boundaries

Water in low-temperature atmospheric-pressure plasmas

pressure plasmas has received growing attention in recent years for the potential use of these plasmas in biomedical applications, air treatment and chemical synthesis. As oxygen, H2O is a good precursor of reactive oxygen species (ROS) and the two can be combined to create cocktails of ROS (O, OH, O3, 1O2, OOH and H2O2) of different compositions. These plasmas tend to be electronegative and display interesting dynamics, particularly when created in small gaps. From a practical point of view, it is important to understand the chemical pathways leading to the production of the biologically relevant ROS, as this will provide guidelines for the optimization of the plasma sources for a particular application

Plasmas for organic synthesis and chemical probes for plasma diagnostics

Although organic chemistry plays a critical role in many plasma applications, there is room for further cross-fertilization between the two disciplines. Here we explore two possible avenues: (1) plasma physics as a new tool for the organic chemist and (2) organic compounds as diagnostics for the plasma physicist

Reaching beyond the surface in plasma treatments

Low temperature atmospheric pressure plasmas have emerged in recent years as a new powerful technology for a wide range of biomedical applications. The potential therapeutic value of these plasmas has already been demonstrated for applications ranging from sterilization of medical equipment to new cancer treatments. With animal and clinical trials underway, the hopes for this new technology are high and the field is developing very rapidly

Comparative study of chemical probes for ozone detection

Plasma composition is typically studied by absorption and emission spectroscopy, mass spectrometry and computational studies. While these techniques provide valuable information about the chemical species in the gas phase, in many applications it is desirable to have a direct measurement of the dose of chemical species delivered to a particular target. For this purpose, chemical probes are particularly interesting as they can provide an inexpensive means for determining the dose of a particular compound. A number of chemical probes have recently been used by the plasma community, particularly those working in plasma medicine and with plasmas interacting with liquids. Generally, however, these probes were not initially intended for use in plasma environments and therefore, it is important to assess their suitability and identify any selectivity issue that could affect the correct interpretation of the measurements. Here, we report on a comparative study of three chemical probes aimed at the quantitative detection of ozone (Table 1): Indigo Carmine and two DCF-derived fluorescent probes

Fluorescence probe for determining the ozone dose delivered by plasmas

Plasma composition is typically studied by absorption and emission spectroscopy, mass spectrometry and computational studies. While these techniques provide valuable information about the chemical species in the gas phase, in many applications it is desirable to have a direct measurement of the dose of chemical species delivered to a particular target. In this work, we will use a fluorescent chemical probe in order to characterize actual flux of ozone experienced by a target exposed to plasma

Emerging applications of low temperature gas plasmas in the food industry

The global burden of foodborne disease due to the presence of contaminating micro-organisms remains high, despite some notable examples of their successful reduction in some instances. Globally, the number of species of micro-organisms responsible for foodborne diseases has increased over the past decades and as a result of the continued centralization of the food processing industry, outbreaks now have far reaching consequences. Gas plasmas offer a broad range of microbicidal capabilities that could be exploited in the food industry and against which microbial resistance would be unlikely to occur. In addition to reducing the incidence of disease by acting on the micro-organisms responsible for food spoilage, gas plasmas could also play a role in increasing the shelf-life of perishable foods and thereby reduce food wastage with positive financial and environmental implications. Treatment need not be confined to the food itself but could include food processing equipment and also the environment in which commercial food processing occurs. Moreover, gas plasmas could also be used to bring about the degradation of undesirable chemical compounds, such as allergens, toxins, and pesticide residues, often encountered on foods and food-processing equipment. The literature on the application of gas plasmas to food treatment is beginning to reveal an appreciation that attention needs also to be paid to ensuring that the key quality attributes of foods are not significantly impaired as a result of treatment. A greater understanding of both the mechanisms by which micro-organisms and chemical compounds are inactivated, and of the plasma species responsible for this is forming. This is significant, as this knowledge can then be used to design plasma systems with tailored compositions that will achieve maximum efficacy. Better understanding of the underlying interactions will also enable the design and implementation of control strategies capable of minimizing variations in plasma treatment efficacy despite perturbations in environmental and operational conditions

Reactive oxygen species production in atmospheric-pressure low-temperature He+O2+H2O plasmas

Low-temperature atmospheric pressure plasmas have received growing interest in recent years, due to their increasing popularity in technological and biological applications. There are many advantages to using these plasmas, for example, they are relatively cheap to run as they do not require expensive vacuum equipment, they are portable, they can be run at near room temperature and they can create complex reactive chemistries inside and outside the discharge region

Reaching beyond the surface in plasma treatments

Cold atmospheric pressure plasmas have been shown to possess bactericidal potential. Many research groups are looking into developing biomedical applications for plasma; however some big questions still remain. There are several main hurdles that need to be jumped before plasma has a chance to break through into the medical treatments market, one of these is penetration. Can plasma penetrate beyond the surface and reach cells beyond those on the surface? Can we make plasma treatments to penetrate, for example, through skin

Continuous flow ozonolysis using atmospheric plasma

Ozonolysis is widely used in organic synthesis to obtain aldehydes and ketones from alkenes, a process of great interest, for example, for the pharmaceutical industry. This reaction is more environmentally accepted than other alternative oxidations and it has good atom efficiency. Ozonolysis, however, has an important drawback; the ozonides generated as intermediates in the process are unstable and pose a risk of explosion. To minimize this risk, continuous flow processing can be used, as this eliminates the accumulation of large amounts of hazardous intermediates, thereby offering an alternative to batch processing that greatly enhances the control and safety of the ozonolysis process.1,2 Here we report on the results obtained with an air plasma-driven continuous-flow ozonolysis system. (... continues