Biodeactivation of lipopolysaccharide correlates with surface-bound NO₃ after cold atmospheric plasma treatment

Cold atmospheric plasma (CAP) treatment of biological surfaces results in important changes of biological functions, but little knowledge on specific surface-chemical changes is available. We measured surface-bound NO₃ on polymer and biomolecular films after CAP treatment. An O₂/N₂-based surface microdischarge was used to deactivate lipopolysaccharide (LPS), an immune-stimulating biomolecule found in Gram negative bacteria. The observed LPS biodeactivation was highest for low N₂ concentrations in O₂, increased roughly linearly with surface NO₃, and then saturated. NO₃ was also observed after treatment by a very different source: an atmospheric pressure plasma jet operating with an Ar carrier gas. Thus, NO₃ formation is a generic surface chemical modification of these materials by CAP sources. We report on measurements of surface-bound NO₃ on a variety of materials after treatment by both an atmospheric pressure plasma jet and surface microdischarge. This species forms on polymers containing neither nitrogen nor oxygen, indicating that it forms in the gas phase. The concentration of surface-bound NO₃, not general oxidation, correlates with the biodeactivation of lipopolysaccharide, a pyrogenic biomolecule. This is the first attempt to correlate a specific surface moiety with biological function.