Cold atmospheric plasma-induced acidification of tissue surface: visualization and quantification using agarose gel models

The biological effects induced by cold atmospheric plasmas (CAPs) on human tissues are mainly due to the production of reactive oxygen and nitrogen species (RONS). Some RONS are also responsible for pH lowering of the treated medium. The CAP-induced acidification has beneficial effect on biological tissues, contributing to the anti-bacterial effect and to the healing improvement observed in treated wound. In this work we investigated the local acidification induced by a helium CAP treatment using tissue models made of agarose gels with adjusted pH around 7.4 to mimic generic organs or around 5.5 to simulate skin surface pH. Using fluorescein as a pH-sensitive fluorescent marker, we developed a useful technique to visualize and quantify the local acidification induced by CAP exposure of tissue surface. The different capillaries used to produce the plasma jet, the treatment time, the initial pH of the surface and the buffer capacity of the tissue model were shown to modulate both the size of the impacted surface and the intensity of the pH decrease. The proposed technique can be advantageous to study the acidifying effect induced by plasma. This method can help to plan safe and controlled plasma treatments in order to avoid hyper-acidification of the tissue, especially when a localized treatment is administered.