Combined effect of protein and oxygen on reactive oxygen and nitrogen species in the plasma treatment of tissue

The influence of protein and molecular, ground state oxygen (O₂) on the plasma generation, and transport of reactive oxygen and nitrogen species (RONS) in tissue are investigated. A tissue target, comprising a 1mm thick gelatin film (a surrogate for real tissue), is placed on top of a 96-well plate; each well is filled with phosphate buffered saline (PBS, pH 7.4) containing one fluorescent or colorimetric reporter that is specific for one of three RONS (i.e., H₂O₂, NO₂^-, or OH^•) or a broad spectrum reactive oxygen species reporter (2,7-dichlorodihydrofluorescein). A helium cold atmospheric plasma (CAP) jet contacts the top of the gelatin surface, and the concentrations of RONS generated in PBS are measured on a microplate reader. The data show that H₂O₂, NO₂^-, or OH^• are generated in PBS underneath the target. Independently, measurements are made of the O₂ concentration in the PBS with and without the gelatin target. Adding bovine serum albumin protein to the PBS or gelatin shows that protein either raises or inhibits RONS depending upon the O₂ concentration. Our results are discussed in the context of plasma-soft tissue interactions that are important in the development of CAP technology for medicine, biology, and food manufacturing.