A Comparative Study of Polymer and Biomolecule Surface Modifications by an Atmospheric Pressure Plasma Jet and Surface Microdischarge in Controlled Environments

In this work, polymer- and lipopolysaccharide-coated Si substrates were exposed to a surface microdischarge (SMD) and an atmospheric pressure plasma jet (APPJ) in controlled ambients. We seek to understand how plasma-ambient interactions impact biodeactivation and surface modifications by regulating the ambient gas chemistry and the proximity of the plasma to the ambient. A key difference between the SMD and APPJ is that the APPJ needs an Ar feed gas and the SMD does not. By adding small N$_{\mathrm{2}}$/O$_{\mathrm{2}}$ admixtures to Ar, we find that the O$_{\mathrm{2}}$ admixture in the APPJ is a key factor for both deactivation and surface modification. After plasma treatments, we detected a new chemical species on a variety of surfaces that was identified as NO$_{\mathrm{3}}$. We find that NO$_{\mathrm{3}}$ forms even with no N$_{\mathrm{2}}$ in the feed gas, demonstrating that this species forms due to interactions with ambient N$_{\mathrm{2}}$. Despite a very different discharge mechanism, the SMD modifies surfaces similarly to the APPJ, including NO$_{\mathrm{3}}$ formation. The SMD generates large O$_{\mathrm{3}}$ concentrations, which do not correlate with NO$_{\mathrm{3}}$, suggesting that O$_{\mathrm{3}}$ alone is not involved in the NO$_{\mathrm{3}}$ formation mechanism. The authors gratefully acknowledge financial support by the US Department of Energy (DE-SC0005105 and DE-SC0001939) and National Science Foundation (PHY-1004256).