Studies Of Atmospheric Pressure Plasma Jet And Its Application On Sterilization

Recently, much attention has been paid to atmospheric pressure nonthermal plasma jet (APPJ) for its convenient employing without a vacuum and the high efficiency on applications with low temperature treatments, especially on the heat-sensitive materials and biological tissues, such as plastics, rubbers, foods, fiber, and skin. Unfortunately, it is still unclear about underpin physics of discharge mechanism and chemical characteristics, such as the active species produced in APPJ. Furthermore, the mechanism of plasma sterilization is on-going studied worldwide currently. Here, the studies of discharge mechanism and chemical characteristics of APPJ are carried out, which is correlated to the effectiveness and efficiency of plasma sterilization. It helps the understanding of interaction between the plasma and micro-organisms, also progresses the medical applications of APPJ.In this study, an APPJ device is developed and characterized by the optical emission spectroscopy (OES), intensified charge-coupled detector (ICCD) and gas temperature measurements. The bacterial of Staphylococcus aureus is selected as the sample for APPJ sterilization. The sterilization mechanism of APPJ is proposed based on the parametric studies of APPJ characteristics and sterilization, especially on the amplitude of applied voltage.The OES measurements show the different active species and free radicals produced in APPJ, such as N2, N2+, He, OH and O, whose intensities grow with the increasing of applied voltage. It is also found that the length of plasma jet in ambient air increases with the gas flow rate and the plasma jet is composed of a hypersonic "plasma bullets", which is shown by the plasma images with the exposure time of Ins. The traveling speed of "plasma bullet" is estimated to be about 20 km/s with the peak-to-peak value of applied voltage (Vpp) of 15 KV. With higher applied voltage, the plasma bullet can be elongated and the multi-plasma bullets (2 bullets) are found at Vpp of 16.5 KV, and eventually the "plasma bullet" becomes the "strip" at Vpp of 18 KV.It is shown that the sterilization effect by the APPJ is not significant with the Vpp of 15 KV and the million of Staphylococcus aureus cells can be inactived within 180s and 120s with the Vpp of 16.5 KV and 18 KV, respectively, which suggests the efficiency of sterilization by APPJ. The scanning electron microscope (SEM) images of cells before and after APPJ treatment demonstrate the cracks, holes on the cells surface, and leakage of intracellular material around the cell, which suggests the effectiveness of sterilization by APPJ.According to the sterilization results by the APPJ, the plasma sterilization mechanism is attributed to the charged particles and reactive particles generated in APPJ, such as N2+, OH and O, by etching and damaging the cells and DNA. On the other hand, the temperature and UV rays in the APPJ are not the important issues in plasma sterilization.