In order to study the impact of different gas compositions on the bactericidal efficiency of cold atmospheric plasma jets, a device with a controlled atmosphere is built. Various mixtures of argon and helium with air are studied regarding their sterilizing effect on Escherichia coli in solution. Bacteria reduction rates react fundamentally different on addition of air in both gases. In case of helium, a distinct maximum for small admixtures is observed. Several diagnostic techniques were applied to the plasma. Stronger formation of peroxynitrous acid due to higher concentrations of hydrogen peroxide and nitrite is found to be responsible for the observed trends and differences. The presented findings are important for the development of efficient treatment devices.

In this study, our aim is to compare the inactivation of bacteria by direct plasma exposure of bacterial solution and plasma activated water (PAW) using a surface micro-discharge (SMD). Four potential factors which could affect both treatments were tested, namely the effect of low dose reactive oxygen species (ROS) pretreatment, enzymatic defence mechanism against oxidative stress, extracellular molecules, and mass transfer in liquid. We applied two power modes of the SMD, i.e. low power ozone mode and high power mode, to inactivate () in distilled water either by direct treatment (DT) or PAW. ROS pretreatment was tested by 30 M of , while superoxide dismutase (SOD) and catalase were used to investigate the effect of enzymatic antioxidant defense. Furthermore, the effect of extracellular molecules was examined by centrifuging and mass transfer in liquid by vortexing. In addition, reactive species in the solution were measured by titanium sulfonate, and nitrite/nitrate colorimetric method for , and and , respectively. Results indicate that vortexing and centrifuging significantly influence the bacterial reduction, while pretreatment could not induce resistance of bacteria against plasma treatment. Enzymatic antioxidants of SOD and catalase could potentially effect the inactivation and plasma chemistry yet only if the concentrations are sufficiently high. We assume that the continuous generation of peroxynitrite is crucial in plasma inactivation for both DT and PAW under high power condition, while under low power condition, long-term bactericidal affects are limited due to the decomposition of ozone by nitrite.

Potential in biomedical-related applications by atmospheric pressure plasma-treated water gradually increased recently. In order to enhance the generation of reactive species in atmospheric pressure plasma in regards to liquid treatment, this study aims to investigate the effect of external axial magnetic field on a helium atmospheric pressure plasma jet (APPJ) and plasma-irradiated water. Magnetic field strength up to 2.0 T was generated by an electromagnet in Helmholtz configuration. The dielectric barrier discharge-based APPJ is driven by 4.4 slm helium and sinusoidal 30 kHz, 10 k V p p signals. Plasma was mainly characterized by optical emission where vibrational and rotational temperature was estimated by nitrogen second positive system, and electron temperature and density by emission intensity line ratio method. Representative reactive species of nitrite, nitrate, and hydrogen peroxide concentration in the plasma-treated water were also quantified. Results of vibrational temperature and electron density showed a first drop then rise trend which partially corresponds to the reactive species in the plasma-treated water. No significant changes were found in rotational temperature, while electron temperature monotonically increased with the magnetic field.

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