| AVS 58th Annual International Symposium and Exhibition | |
| Plasma Science and Technology Division | Monday Sessions |
| Session PS+BI-MoA |
| Session: | Multiphase (Liquid, Solid, Gas) and Biological Related Plasmas |
| Presenter: | Elliot Bartis, University of Maryland, College Park |
| Authors: | E. Bartis, University of Maryland, College Park T.-Y. Chung, University of California, Berkeley N. Ning, University of California, Berkeley J.-W. Chu, University of California, Berkeley D.B. Graves, University of California, Berkeley J. Seog, University of Maryland, College Park G.S. Oehrlein, University of Maryland, College Park |
| Correspondent: | Click to Email |
Low temperature plasma (LTP) treatment of surfaces is a promising path toward sterilization of bacteria [1]. Past works have shown plasma-induced degradation of bacteria [2], but little knowledge exists regarding the plasma-induced chemical modifications in biomolecules that result in inactivation since various plasma species, e.g. ions, reactive radicals, and UV/VUV photons may aid in inactivation. Lipopolysaccharides (LPS) are a main component of the outer membrane of gram-negative bacteria and are difficult to remove from surfaces by conventional methods [3]. LPS is made up of a polysaccharide chain and lipid A and lipid A elicits an immune response in animals [1]. Previous studies have found that adding H2to an Ar plasma leads to a reduction of infrared bands originating from the aliphatic chains of lipid A, namely C-Hx stretching, C-O, and amide bands [4]. This study aims to distinguish the roles of physical sputtering, chemical attack by H-atoms, and plasma-generated VUV. LPS-coated silicon chips were exposed to LTP (Ar, H2, and Ar/H2 mixtures) to explore the effects of plasma composition/ion energy on the etch rates (ER) and chemical and optical properties of LPS. Real-time in-situ ellipsometry was used to monitor ER and changes in the LPS film’s optical density during plasma exposure. The real-time data showed that Ar plasmas create a dense film on the surface that decreases in density with H2addition. The films were etched fastest in Ar discharges mixed with ~10% H2and were slowest in pure H2. Since previous work [4] found that adding H2to an Ar discharge enhanced sterilization, these results may indicate that chemical modification rather than rapid erosion may be more important for inactivation. After LTP treatment, samples were characterized by vacuum-transfer to x-ray photoelectron spectroscopy (XPS) to measure the chemical modifications taking place in the LPS layer. With XPS, we measured a decrease in the intensity of the C-C/C-H peak, which indicates that the aliphatic chains in lipid A were removed. The N/C ratio increases approximately equally in all discharges, which suggests that gas chemistry does not have a large impact on amides. Complementary studies with Lipid A will be presented as well as results of a VUV optical filter approach used to probe VUV-induced LPS modifications in real time by in-situ ellipsometry while protecting the material against ion bombardment.
[1]A. von Keudell et al., Plasma Process. Polym. 7, 327 (2010)
[2]H. Rauscher et al., Chem. Phys. Chem. 11, 1382 (2010)
[3]E. T. Rietschel et al., FASEB J. 8, 217 (1994)
[4]O. Kylian et al., Plasma Process. Polym. 5, 26 (2008)