Generation mechanism of hydroxyl radical species and its lifetime prediction during the plasma-initiated ultraviolet (UV) photolysis

Abstract

Through this work, we have elucidated the mechanism of hydroxyl radicals (OH(•)) generation and its life time measurements in biosolution. We observed that plasma-initiated ultraviolet (UV) photolysis were responsible for the continues generation of OH(•) species, that resulted in OH(•) to be major reactive species (RS) in the solution. The density and lifetime of OH(•) species acted inversely proportional to each other with increasing depth inside the solution. The cause of increased lifetime of OH(•) inside the solution is predicted using theoretical and semiempirical calculations. Further, to predict the mechanism of conversion of hydroxide ion (OH(-)) to OH(•) or H2O2 (hydrogen peroxide) and electron, we determined the current inside the solution of different pH. Additionally, we have investigated the critical criterion for OH(•) interaction on cancer cell inducing apoptosis under effective OH(•) exposure time. These studies are innovative in the field of plasma chemistry and medicine.

Figure 1

(a) Optical emission spectrum measured by CCD spectrometer with optical fiber at the 2 mm above and below region, respectively, of the DI water under Ar plasma jet bombardment onto the biosolution surface with inclusion of Ar gas in glove box; (b) Lifetimes for various ROS measured at ambient air region of 2 mm above the water surface without Ar glove box by using the monochromator; (c) Temporal behaviors of 309 nm for OH^• emission intensity for different depth locations of 2 mm, 4 mm, and 6 mm inside the DI solution with quartz filter located at 1 mm depth position of water during Ar plasma jet bombardment; (d) Lifetimes of OH^• vs water depth positions for 2 mm, 4 mm, and 6 mm from the surface.

Figure 2

(a) Visual observation for generation of OH^• species inside the DI water and PBS when the UV mercury lamp has been irradiated onto their surface; (b) Visual confirmation for generation of H₂O₂, inside the DI water either by irradiation of UV or plasma bombardment onto the water surface with quartz filter located just below the DI surface; (c) OH^• density vs the external H₂O₂ concentrations in DI water at 4 mm depth position, when the Ar plasma jet has been bombarded; (d)Density of OH^• vs the depth positions of the DI water and PBS solutions, generated by Ar plasma jet operated in Ar glove box, under the low electrical power of 4.9 W and driving frequency of 35 kHz.

Figure 3

(a) Cell death area's ratio, which is calculated by ratio of cell death area of PI (Propidium Iodide: dead) stained region to NTP plasma exposed area whose diameter is 1 cm, of lung cancer H460 cells and SEM images of lung cancer H460 cells for the control and Ar plasma treatment by 60 s, adhered at 2 mm, 4 mm, and 6 mm depth positions of PBS, respectively; (b) Ion-induced secondary electron emission coefficient (γ) for lung cancer H 460 cell surfaces for the controls and plasma treated cells by 60 s, respectively, versus the incoming He ion energy ranged from 140 eV to 200 eV; (c) Molecular surface energy distribution of the lung cancer H460 cells for the control and Ar plasma treated.

Figure 4

(a) Setup to determine different amount of current generated during plasma bombardment in different pH solution; (b) Visual test of H₂O₂ generation at different pH in the presence of titanyl ion after plasma bombardment; (c) Absorbance spectra of DI water before and after the Ar plasma treatment at different pH. To confirm the different concentration of H₂O₂ generation at different pH in the presence of titanyl ion.