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Graduate Student Seminar - 11/11/2011

"Deactivation of Pyrogenic Biomolecules by Ar/H2 Inductively Coupled Plasmas"

by Elliot Bartis

Friday, November 11, 2011 -- 12:00 p.m.
Large Conference Room, 1207 Energy Research Facility

Advisor:  Professor Gottlieb Oehrlein

Low temperature plasma (LTP) treatment of surfaces is a promising path toward sterilization of bacteria. Past works have shown plasma-induced degradation of bacteria, but little knowledge exists regarding the plasma-induced chemical modifications in biomolecules that result in inactivation since various plasma species, e.g., ions, reactive radials, 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. LPS is made up of a polysaccharide chain and lipid A, and lipid A elicits an innate immune response in animals. Previous studies have found that adding H2 to 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. 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. The films were etched fastest in Ar discharges mixed with 20% H2 and were slowest in pure H2. Since previous work found that adding H2 to 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. XPS analysis suggests that H2 plasmas are more effective at removing carbonyl groups. 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.

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