Production of energetic metastable nitrogen species for sterilization of chemically-sensitive medical equipment (Topic 22a)

Research into cold atmospheric-pressure plasmas for decontamination and sterilization has been rapidly increasing. Such plasmas are often operated in ambient air, making plasma / biomatter interaction mechanisms difficult to identify and control. In addition, such discharges always produce some level of ozone, which is incompatible with many materials used in medical practice. Physical Sciences Inc. (PSI) proposes to employ our existing electrically efficient, compact, microwave-driven non-equilibrium discharge for operation in nitrogen, using the energetic discharge effluent for sterilization of plastic and rubber medical equipment. Electronically- and vibrationally-excited states of nitrogen are energetic but are chemically less reactive than oxygen-containing species, and have previously been shown to be capable of both deactivating bacterial species and persisting far downstream of an active discharge region. Such excited species of nitrogen will be generated in the proposed work by passing nitrogen gas through the active region of a microwave-generated plasma. The unique microwave discharge design to be used in this project has previously been shown to be extremely efficient at generating large fluxes of excited atomic and molecular species in other gases at atmospheric pressure; preliminary measurements indicate that this efficiency translates to excited nitrogen as well. The microwave resonator-based discharge allows the generation of a stable, dense plasma operating in true steady-state. The excited nitrogen species in the discharge effluent will be measured downstream of the active plasma using a combination of emission and absorption spectroscopy, and evaluated via a kinetics model of nitrogen energy transfer, and will draw upon PSI’s long history of work with energy transfer in excited nitrogen to ensure correctness. Bactericidal effectiveness will be measured through exposure of representative bacteria species to the discharge effluent in both simplified and realistic device geometries. Many medical devices are made from plastics, rubber, or other thermally- and chemically- sensitive materials, limiting the options for sterilization. Ethylene oxide gas is widely used to treat such devices, but this gas is both toxic to workers and highly flammable. Alternative techniques include gamma ray or electron-beam irradiation. Each of these options impose significant safety burdens and associated costs onto users. A nitrogen discharge producing a sufficient flux excited nitrogen molecules to sterilize medical devices would largely eliminate safety concerns.