Rsc_cp_c001188f 7779..7781

The use of non-thermal plasmas in bio-medical applications has been driven by the development of cold plasma devices capable of being operated in the open atmosphere. The generation of atmospheric pressure plasmas removes the need for costly high vacuum systems and avoids the inherent difficulties of treating living tissue under vacuum conditions. Moreover, since such plasmas are ‘cold’ they are ideal for treating materials that are easily damaged by high temperatures, e.g. soft plastics and biological media, indeed exposure of any cellular material to temperatures only a few degrees higher than ambient may cause irreparable damage. A recent extended review provides an update on research related to applications of non-thermal plasmas in medicine and a discussion of the possible mechanisms of interactions between plasma and living matter. In this review the authors presented a very broad overview of the use of ‘cold’ plasmas in the clinic including: tissue sterilization, wound healing, tissue regeneration, treatment of melanoma skin cancer and dental cavities. However, these applications are still in the earliest stage of their development and their introduction into general medical practice may be some years away. The main reason for this is a lack of a deeper understanding of the physical, chemical and biological mechanisms underlying the interaction of a nonthermal atmospheric pressure plasma and living cells, tissues and organs. In the present work we have investigated the formation of singleand doublestrand breaks in DNA molecules induced by an atmospheric pressure plasma jet (APPJ). The complexity of plasma-generated species, i.e. excited atoms and molecules, charged particles, electrons and UV light gives a variety of possible pathways by which DNA can be damaged. Therefore, our aim is to understand the interaction of particular components of the plasma with DNA. A schematic view of the experimental set-up is presented in Fig. 1. Two tubular metal electrodes are separated by a 3 cm gap. A quartz cylindrical tube is inserted between the electrodes and helium is flowed through the tube with the velocity of 10 m s . The two electrodes are connected to a RF power supply capable of producing sinusoidal shaped voltage pulses with an amplitude of 4 kV and repetition rate of 3.2 kHz. A discharge is ignited in the gap between electrodes; the discharge current typically reaches a peak value of 19 mA under these conditions. The mean power transferred into the discharge is around 20 W. At the open end of the reactor a plasma plume is launched into the surrounding air. The general working principle of the generation of such plasma jets is described by Kedzierski et al. In this experiment we used extra-chromosomal plasmid DNA (pBR322, 4361 base pair) extracted from E. coli bacteria and purified to ensure only a relatively small amount of residual proteins. Plasmid DNA was dissolved in autoclaved ultra-pure water and 2 mL of such an aqueous DNA (200 ng mL ) solution was deposited onto mica slides that were then dried at room temperature. The DNA covered mica slides were then placed perpendicularly to the ‘cold’ plasma jet formed in helium. Samples located at the tip of the jet were exposed for different time durations. It should be noted that the temperature of the tip of the plasma jet was measured using a mercury thermometer and a thermocouple and was found to be no more than 10 1C above ambient. Thus, no significant thermal effects on the plasmid DNA are expected. Moreover, control experiments were also performed by leaving a few samples at room temperature, while the other samples were treated. In this control measurement, 85–75% of intact DNA was recovered from the mica slides. Additionally, experiments were also performed, where the dry DNA samples were exposed to a