, D. (2011). Cold atmospheric pressure plasma jets as sources of singlet delta oxygen for biomedical applications.

The effect of a cold (<40 °C) radio frequency-driven atmospheric pressure plasma jet on plasmid DNA has been investigated. Gel electrophoresis was used to analyze the DNA forms post-treatment. The experimental data are fitted to a rate equation model that allows for quantitative determination of the rates of single and double strand break formation. The formation of double strand breaks correlates well with the atomic oxygen density. Taken with other measurements, this indicates that neutral components in the jet are effective in inducing double strand breaks.

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Cold atmospheric pressure plasmas offer a unique environment for treatments of soft materials, including biomaterials and living tissue. Single plasma devices can be as small as micro-meters allowing very precise treatments reducing damage to surrounding healthy living cells. It is essential to correlate direct plasma parameters with effects on bio-materials. There are various energy carrying species in the plasma such as charged particles, excited neutrals, radicals, and photons. In particular radical oxygen species ROS e.g. O, OH, have been identified as important.Little is known of the influence the plasma has on DNA, this is vital to quantify before any potential application on living tissue can be realized. In this study we quantify the influence a cold plasma has on plasmid DNA and simultaneously measure absolute densities of ground state atomic oxygen (Diagnostic based Modelling) and helium metastables (laser absorption spectroscopy) for direct correlation.An RF atmospheric pressure plasma jet configuration, operated in helium and oxygen, is used for application on plasmid DNA to determine the nature of the influence on DNA. The effluent of the plasma interacts with pCDNA3.1 plasmid DNA for varying treatment times and various plasma conditions. Three different buffers -water, phosphate buffered saline (PBS), and Tris-EDTA are used. After irradiation an electrophoresis technique is used to separate out the different DNA constituents supercoiled, open circular and linear. A rate equation model is used to fit the experimental data and determine the rate of single strand breaks (SSBs) and double strand breaks (DSBs). This allows for greater understanding of the processes involved in DNA damage. While SSBs are easily repaired since the damaged strand can replicate the undamaged strand, DSBs are more serious and incorrect repair can lead to DNA mutations or even cancer.Absolute atomic oxygen densities and helium metastable densities are measured in the plasma bulk for correlations to the influence on DNA. Double strand breaks require more energy or a second single strand break within 10 DNA base pairs of the first (where a typical strand of the DNA used has 5400), and so there are significantly fewer linear breaks. With increasing power, and increasing atomic oxygen densities and helium metastables, an increase in both single and double strand break rates are observed. Significantly less damage is observed in the Tris-EDTA solution, indicating the role of radicals in damage.

Study of the effects of microplasmas on living tissue has been prolific in recent years [1]. However, while there are many desirable outcomes of using such devices, on for example chronic wounds, in order to safely use these plasmas the long term effects must be considered.Here a 13.56 MHz RF plasma is formed between two stainless steel electrodes with 1 mm gap distance. It was previously found that a helium-based plasma with a small admixture of 0.5 % oxygen was effective in causing DNA damage [2]. Here, this was further explored, introducing small admixtures (up to 2 %) of oxygen, argon or nitrogen. The plasma was operated with constant moderate power. The singlet delta oxygen, ozone and atomic oxygen densities in this source have been measured [3,4].The effect of plasma exposure to plasmid DNA was studied. Damage was considered to be an event wherein a single or double strand break was created.The exit of the plasma source was placed 3.2 mm from plasmid DNA for times varying from 1-10 seconds. The DNA was analysed for the different components using gel electrophoresis and from these results the rates of single and double strand break damage can be obtained [5].It was found that helium with added oxygen produced a greater rate of both double and single strand breaks. The damage with oxygen introduced to the helium gas flow was compared to singlet delta oxygen (SDO), ozone and atomic oxygen densities in the plasma and a positive correlation between the amount of SDO and the amount of single and double strand breaks was evident. Conversely, nitrogen lowered DNA damage by a factor of 3, and in fact for most cases reduced the damage below that of pure helium.

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