BIOPLASMAS & PLASMAS WITH LIQUIDS - Joint Conference of COST ACTIONS TD1208 “Electrical discharges with liquids for future applications” & MP1101 Biomedical Applications of Atmospheric Pressure Plasma Technology, Bertinoro, Italy, 13th-17th September 2015 OH in an Atmospheric Pressure Plasma Jet and its Reactivity with Fatty Acid Methyl Esters L. M. Martini1, M. Scapinello2, G. Bortolotti1, G. Dilecce1,3, G Guella1, M. Scotoni1, P. Tosi1 1 Dipartimento di Fisica Università di Trento, via Sommarive 14, 38050 Trento - Italy 2 CNR-IMCB, UOS Trento, via Sommarive 14, 38050 Trento - Italy 3 CNR - Istituto di Nanotecnologia, via Amendola 122/D, 70126 Bari - Italy Atmospheric-pressure plasma jets (APPJ) allow to generate reactive oxygen species (ROS), such as OH, O, O3 and O2(a1Δg). For this reason, these discharges are of interest in sterilization and other biomedical applications . From the viewpoint of basic research, APPJs can be utilized to investigate radical-initiated oxidation processes . We used laser induced fluorescence (LIF) to measure the OH concentration in a radio-frequency APPJ of He/H2O . The jet plume impinges over the surface of a liquid target, composed of fatty acid methyl esters (FAMEs). OH radicals produced in the discharge may thus trigger the reactivity of unsaturated FAMEs. We choose this class of compounds as a simplified model of cellular membrane constituents. The gas composition in the Jet-surface contact zone is of great importance for the relative abundance of ROS produced by the jet. As shown by model calculations, in He-H2O mixtures OH is the most abundant specie, while the other ROS, in particular atomic oxygen, have a factor of 2-3 lower concentration . The addition of O2 to the mixture greatly enhances the production of O, O3 and O2(a1Δg) . Air penetration in the Jet plume attains a similar effect . Our RF APPJ is equipped with a concentric He flow creating a He gas jacket that greatly limits air intake in the jet region. This has been verified by LIF measurements of humid air concentration in the jet. Changing the feed gas composition, then, we can select two extreme ROS relative abundance conditions: (a) with He-H2O gas feed and very small air penetration, a condition with OH concentration about two times larger than that of the other ROS; (b) with He-O2 gas feed and residual water from gas feed tubes, a condition with O, O3 and O2(a1Δg) concentration more than one order of magnitude larger than that of OH. The treatment of fatty acids in the two extreme conditions results into strikingly different products, revealed by chromatographic (GC-MS/HPLC-MS) and NMR techniques. In the first case, in the presence of prevailing OH flux, the main observed effects are the reduction of FAMEs and the formation of dimeric species. In the second condition, at high concentrations of O, O3 and O2(a1Δg), we observed the presence of several oxidized products. The appearance of these species is typical of lipid autoxidation . We carried out LIF measurement over the surface of the target in order to assess a correlation between the OH flux and the FAME reactivity.  A. Fridman and G. Friedman, Plasma Medicine, John Wiley & Sons Ltd (2013).  J. V. der Paal, S. Aernouts, A. C. T. van Duin, E. C. Neyts and A. Bogaerts, J. Phys. D: Appl. Phys., 46 (2013) 395201  G. Dilecce, L. M. Martini, P. Tosi, M. Scotoni and S. De Benedictis, Plasma Sources Sci. Technol. 24 (2015) 034007  G. V. Naidis, Plasma Sources Sci. Technol. 22 (2013) 035015  K. McKay, D. X. Liu, M. Z. Rong, F. Iza and M. G. Kong, J. Phys. D: Appl. Phys., 45 (2012) 172001  G. V. Naidis, Plasma Sources Sci. Technol. 23 (2014) 065014  E. N. Frankel, Lipid oxidation, Woodhead Publishing Limited (2005).