Helium plasma jet interactions with water in well plates

Abstract

Plasma activation of liquids or cell cultures is a method for investigating the consequences of plasma produced reactive oxygen and nitrogen species (RONS) on living systems. The reproducible transfer of RONS, ions, electrons, and photons to the liquid is critical for determining reaction mechanisms and biological outcomes, and depends strongly on system parameters. A common in vitro method of plasma treatment of cells is a plasma jet directed into a well plate filled (or partially filled) with a liquid cell growth media. This method of treatment intrinsically has several environmental and geometrical factors that could lead to variability in the activation of the media. Uncontrolled or unreported geometrical and environmental factors that affect this transfer can, therefore, influence the reproducibility of measurements. In this paper, results from a numerical modeling investigation of a pulsed helium plasma jet interacting with water in a well plate are discussed while varying the height of the well‐plate rim. The height of the rim changes gas flow patterns, the ratio of He‐to‐air, and the water vapor content in the gas layer above the liquid. With a low rim, gas flowing from the jet stagnates on‐axis and flows radially outward with few vortices that recirculate reactants. With high rims, the gas flow is dominated by vortices and recirculation. With a low rim, the ionization wave (IW) from the jet strikes the liquid and proceeds as a surface IW across the water. With higher rims, the densities of helium and water vapor are higher above the liquid, which results in a volumetric propagation of the IW, initially producing higher densities of H2, HO2, OH, and H2O2. The end result is that for otherwise identical conditions, the densities of solvated H2O2aq and select reactive nitrogen species increase with rim height due to the vortices that recirculate reactants.

Measuring plasma-generated ·OH and O atoms in liquid using EPR spectroscopy and the non-selectivity of the HTA assay

“…However, this difference represents a small fraction of the total peroxide, and reaction rates between DMPO + • OH (k = 4.3 × 10 9 M −1 s −1 ) [53] and • OH combining to H 2 O 2 in the liquid (k = 5 × 10 9 M −1 s −1 ) [56] are similar, eliminating the possibility aqueous • OH radicals are recombining much faster than they can be scavenged. Although gas phase measurements on a COST predecessor using a similar H 2 O admixture indicate • OH and H 2 O 2 densities on the same order at 3 mm from the electrode [22], the Henry's law constant for peroxide is more than three orders of magnitude higher than • OH [57,58]. The tendency for peroxide to transport into the liquid may explain why, despite similar densities in the gas phase, peroxide is much more abundant in the liquid.…”

Guided plasma jets directed onto wet surfaces: angular dependence and control

“…If the density of the liquid species at the surface of the liquid is super-saturated with respect to the gas phase species (that is, the density is higher than the Henry's law equilibrium value), then transport of that species is allowed from the liquid into the gas. The reaction mechanism used in this investigation for He plasma jets into humid air interacting with water is essentially the same as described in [24].…”

Cold atmospheric plasma technology for removal of organic micropollutants from wastewater—a review

“…Pulsed DC corona and DBD plasma over the thin water film are considered most efficient in the degradation of OMPs [71,109,125,127,130] with the efficiencies going to 100%. Higher mass transfer of reaction species from gas to bulk phase with molecular diffusion along with the plasma discharge leads to faster degradation of OMPs [69,150,151]. The thin water film offers a larger surface to volume ratio than other configurations.…”