Study On OH Radical And Its Biological Effect In Surface Discharge Plasma Using Laser Induced Fluorescence Spectroscopic Technique

Since 1990s,atmospheric pressure plasma has become a research hotspot in the field of plasma science where the plasma biomedical applications is the strongly growing branch.The reactive oxygen species?ROS?and reactive nitrogen species?RNS?is considered as the key mediator for the plasma induced biomedical effect.Characterization and unraveling of the ROS/RNS is the key issue for the research of biomedical application of atmospheric pressure plasma.Temporally and spatially resolved diagnosis of the number density of ROS/RNS in the atmospheric pressure plasma is much desired.In the recent years,atmospheric pressure surface discharge plasma as newly developed plasma source,becomes an ideal approach for the ROS/RNS generation and biomedical sample processing.This thesis focused on the diagnosis of temporal and spatial distribution of OH radical,which is considered as key ROS in the plasma.The major works of this theis are summarized as follows:In the chapter 2,a laser induced fluorescence diagnostic system with temporal and spatial resolution ability for ROS/RNS measurement has been established.This diagnostic system integrated an atmospheric pressure surface discharge reactor including high precision synchronization timging AC power supply and nanosecond pulsed DC power supply,gas composition controlling system,a laser beam?sheet?shaping system and ultraviolet fluorescent detecting system.The image BOXCAR technique has been developed,which significantly improved the signal to noise ratio of the whole laser induced fluorescence diagnostic system.The OH?X?radical has been taken as benchmark test and the sensitivity of ppb level,spatial resolution of 100?m and temporal resolution of 20 ns have been achieved.In the chapter 3,the absolute number density calibration on the laser induced fluorescence dignostic system has been carried out based on the laser Rayleigh scattering technique.The multi rotational branches resonance excitation approach using broadband tunable OPO laser has been developed by laser pump scheme of OH?X²?,v"=0?A²?⁺,v'= 1?,where the three rotational transitions Q1?1?,Q21?1?and R2?3?from the ground state OH were resonantly excited.Compared with conventional single rotational branch excitation via tunable narrowband dye laser,this method significantly reduced frequency instability induced by variable temperature.This approach increases calibration accuracy of the absolute number density about five times.In the chapter 4,three dimensional distribution of OH in the helium surface discharge plasma has been measured by the developed laser induced fluorescence diagnostic system.The results indicated that OH could migrate larger length far beyond the prediction by fluid model.Temporal and spatial characterization of OH has been studied by pulsed modulation technique and the results demonstrated that at the short discharge pulse modulation time,the OH migration length was consisted between experiment and fluid simulation;As the discharge pulse modulation time increased,the OH migration length was increased remarkably.Moreover,the VUV spectrum of the surface discharge has been measured and the results indicated that the VUV photondissociation of H₂O would play a minor role in generating OH in large migration length.Hence long lifetime species could be the main mechanism of the OH generation in the large migration length region.In the chapter 5,the evaluation of biological effect induced by helium surface discharge plasma has been implemented for the typical eukaryote Saccharomyces cerevisiae.Under various discharge parameters and OH number density,the influence of OH on yeast cell has been investigated by assessing cell viability,cell morphology and DNA content.The result showed that OH radical was the direct mediator in the damage of yeast cells including cell death,cell membrane rupture as well as DNA fragment,where the plasma generated OH number density played the key role for the yeast cell damage level.