In this work, an actual biological tissue is used to investigate how thick the reactive oxygen and nitrogen species (RONS) produced by a plasma jet can penetrate through the tissue. This is one of the most critical questions in plasma medicine. The concentration of RONS (O3, H2O2, OH, NO2−, NO2− + NO3−) produced by the plasma jet penetrating through different thickness of the tissue is measured. It is found that the reactive oxygen species (ROS) produced by the plasma are significantly consumed by the tissue. For the tissue thickness of 500 μm, there is only about five percent or even less of the ROS (O3, H2O2, and OH) penetrating through the tissue. On the other hand, more than 80% of the reactive nitrogen species (NO2− + NO3−) are able to penetrate through the 500 μm biological tissue. Furthermore, under certain experimental conditions, some of the RONS can penetrate through 1.25 mm of the biological tissue. Finally, besides H2O2, NO2−, and NO3−, there is some other unknown RONS that penetrate through the biological tissue.

In this work, a co-culture system with liver cancer cell line HepG2 and normal cell line L02 is used to investigate the selective effect on cancer and normal cells by plasma activated medium (PAM), which is closer to the real environment where cancer cells develop. Besides, the co-culture system is a better model to study the selective effect than the widely used separate culture systems, where the cancer cell line and normal cell line are cultured independently. By using the co-culture system, it is found that there is an optimum dose of PAM to induce significant cancer cell apoptosis while keeping minimum damage to normal cells.

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Two of the key questions in plasma medicine are how deep the reactive oxygen and nitrogen species (RONS) generated by a plasma can penetrate into tissue and how the liquid (extracellular and intracellular fluid) composition affects the concentration of RONS. In this paper, different thicknesses of pig muscle tissue are used as a tissue mode to investigate the effect of tissue thickness on the penetration of RONS through tissue. Six different types of liquid (inorganic group: double-distilled water (DDW), 1% phosphate-buffered saline, 0.9% NaCl; organic group: 5% glucose, 2% serum and 10% serum solution) are used in the receiving chamber under the tissue in order to try to understand the effect of liquid composition on the penetration of RONS (H 2 O 2 , NO − 2 and NO − 3 ) generated by the plasma. It is found that when a tissue thickness of 500 µm is used the H 2 O 2 concentrations in organic liquids are about 20-30 times higher than in DDW. The NO − 2 and NO − 3 concentrations in serum liquid are much higher than in all other liquids, which might be due to the plasma reacting with amino acids and proteins. Besides, the NO − 3 concentration in organic solution is higher than the NO − 2 concentration for the same experimental conditions. Furthermore, when the serum percentage is increased from 2% to 10%, the NO − 2 concentration increases dramatically but the NO − 3 concentration decreases significantly. This is especially true for a tissue thickness of 500 µm. One novel discovery is the RONS do not only penetrate the tissue by diffusion-there are also reactions between the plasma and the liquid which affect the final RONS concentration.

In this work, reactive oxygen and nitrogen species (RONS) generated by a plasma jet penetrating through and left in the skin after the plasma treatment are measured, and the effects of stratum corneum (SC) on the penetration of the RONS are also investigated. It is found that the RONS generated by the plasma jet can penetrate through the skin, and that the penetration of some kinds of the RONS could be enhanced significantly by tape stripping the SC layer of the skin. Further investigations find that the typical reactive oxygen species, including OH, 1O2, O3, and H2O2, cannot penetrate through the mice skin at all (under the detection limit) no matter whether the SC layer of the skin is present or not, where the thickness of the mice skin is about 200–300 μm. This result is very different from the experimental results obtained from the muscle tissue model and gelatin model. Finally, it is found that high concentrations of long-lived RONS (H2O2, NO2−, and NO3−) are left in the skin after the plasma treatment, which means that the plasma treatment could have a long-time scale therapy effect. This finding is important for the applications of plasma medicine.