This award is made in response to a proposal submitted to and reviewed under the NSF/DOE Partnership in Basic Plasma Science and Engineering joint solicitation NSF 09-596. The award provides funds to support undergraduate participation in the overall research effort, which is being funded separately by the DOE under contract to University of Maryland (Grant DE-FG02-10ER55077).
The proposed research objective is to establish an atomistic understanding of interactions of low temperature plasma (LTP) with prototypical biological assays to achieve biological deactivation. While LTP treatment of biological cells and living tissue at both low and atmospheric pressure has been demonstrated as a versatile method to directly alter biological function of living matter in desirable ways, important scientific knowledge gaps exist and preclude rational development of these procedures. These gaps include understanding of ion-, energetic photon or reactive neutral initiated processes, changes in surface/near-surface properties of the treated biological entities and correlation with altered biological function, and lack of theoretical models capable to assist with interpretation of experimental observations and formulation of a consistent framework. Addressing these knowledge gaps requires an interdisciplinary team of investigators. The combined expertise available to this project includes biological assay methodologies, plasma-surface treatments and in-situ surface characterization, beam-surface interactions and molecular dynamics simulations of plasma/biological materials interactions, and interactions between lipid A/LPS and LBP at the atomic scale simulations using all-atom molecular mechanical force fields molecular dynamics simulations of proteins. The current team is thus positioned to significantly advance the scientific understanding of LTP treatment of biological matter for biological deactivation.
Successful completion of the project will provide the scientific foundation for LTP-based disinfection of medical instrumentation, packaging for food and medicines, other surfaces, and decontamination of biological warfare agents. The principles under study in this project are relevant to all applications of LTP to biological systems, cells and tissue, including the growing field of plasma medicine. The interdisciplinary character of this research provides unique educational opportunities for the students and faculty
The NSF support of undergraduate participation adds a broader educational impact through the early-year training of students by introducing them to scientific research as a possible career path.
Low temperature plasma treatments have been shown to degrade bacteria and deactivate biomolecules. However, a major knowledge gap existed regarding which plasma species, e.g. charged species (ions), ultraviolet energetic light, and reactive atoms or molecules (radicals), are responsible for the modifications required for deactivation. Lipopolysaccharide (LPS) and lipid A, the toxic element of LPS, are the main components of the outer membrane of Gram-negative bacteria and difficult to remove from surfaces by traditional sterilization methods, and used as representative biomolecules in this work. In the first part of this study, various approaches were used to isolate the different plasma species to examine their effect on the biological activity of the LPS and lipid A biomolecules (see Fig. 1). This work showed that besides etching and ultraviolet light induced biomolecule changes subtle biomolecular changes due to atomic species can lead to the deactivation of biomolecules. These modifications can inhibit the binding of receptor molecules, whose binding depends on a variety of interactions such as hydrophobic and electrostatic interactions and lock-and-key mechanisms where binding is conformation-dependent. Complementary, collaborative work at UC-Berkeley involved beam experiments. The clarification of the role of ions, high energy photons, and radicals in deactivation of biomolecules established in this work has broad implications for the emerging field of plasma medicine where plasma species interact with sensitive, biological matter. A key finding that reactive neutral species can deactivate and modify surfaces covered with biomolecules with negligible etching motivated studies of using plasma sources operated at atmospheric pressure where neutral species dominate the interaction with surfaces. The range of applications of small atmospheric pressure plasma devices as shown in Fig. 2 is growing rapidly. These sources have been used for thin film deposition, medical decontamination of surfaces, and cancer treatment, to name just a few. However, a mechanistic understanding of plasma-surface interactions at atmospheric pressure is lacking. How do these sources interact with the environment? Can this interaction be regulated to control surface modifications? To answer these questions, we used an atmospheric pressure plasma jet in an isolated chamber that can be evacuated and is interfaced to a surface analysis system, allowing us to study surface modifications under well-controlled conditions. High-speed photography was used to observe how the effluent changes from an air environment to one that matches the feed gas. For Ar and N2/Ar plasma, we see that the plume size increasing dramatically when the environment matches the feed gas, but is much smaller regardless of environment for the O2/Ar plasma (see Fig. 3). Even though the plume is much smaller for O2/Ar plasma, the surface modifications are consistently the strongest. We exposed the same biomolecules described above to atmospheric plasma in various environments. The plasma creates a variety of species that can modify the film including reactive oxygen and nitrogen species such as atomic O, NOx, metastable O2, and ozone. We find that plasma-environment interactions strongly influence the species that reach the surface. For example, atomic O reacts with nitrogen to form NOx. This consumption impacts the degree of deactivation observed, as we have found that O2/N2 mixtures, which create NOx, are less effective than O2 alone, which creates atomic O (see Fig. 4). Our work in controlled environments demonstrates that the efficacy of using APP sources for material modifications depends strongly on the environment in which it is performed. Treatments likely will differ if they are performed in a dry desert or a humid rainforest. In addition, the results of this work guides the design of future APP sources since the plasma-environment interaction can be used to tune the density and type of reactive species striking a surface, as required for many applications.
