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UBC Theses and Dissertations

Studying microbial inactivation by a new UV radiation source : microplasma UV Raeiszadeh Oskouei, Milad


Pathogenic microbes are quickly becoming one of the biggest human health threats of our time. Ultraviolet (UV) radiation enables the optogenetic control of microorganismal replication without requiring chemical addition. However, microbes with UV-resistant and repairable nucleic acids have challenged the germicidal efficiency (GE) of present UV sources. In this regard, targeting intercellular proteins responsible for nucleic acid excitation, repair, and infection can be the solution. The newly-emerged microplasma UV technology is capable of irradiating far-UVC (200 – 240 nm) with unique spectral power distributions in a flat form, which opens new pathways for the development of novel UV disinfection systems. This study is the first to identify the mechanism-analyzed and kinetic-modelled GE of microplasma UV, radiating around proteins UV-absorption and decomposition peak. The microplasma UV lamp is initially characterized in terms of radiation profile and the impact of operating parameters on the power output. It is shown to be an instant-on and fast stabilized source. The radiant power output is a linear function of the electrical current and is not influenced by the lamp operating temperature and intermittent on/off cycles. Afterwards, a protocol is also developed for obtaining reliable kinetic data for microplasma UV-induced reactions. An experimental setup is proposed for the kinetic studies, where the characteristics of the incident irradiance of the lamp, including uniformity, collimation, and divergence, are quantitatively evaluated. Two studied cases of microbial inactivation and the chemical photo-initiated oxidation in individual protocol-based setups confirm the reproducibility of the fluence-based kinetic data independent of the reactor size. Eventually, the GE of microplasma UV is studied against two surrogates for challenging microorganisms, Escherichia coli (E. coli) and bacteriophage MS2, and compared with literature values for current UV sources: about 2-fold GE for MS2 inactivation and one-third repair for E. coli is achieved. Emitted microplasma UV photons induce significant nucleic acid repair deficiency disorder and dramatic infection proteins excitation to enhance the genome inactivation. The reactive oxygen species are found to not play a role in this enhancement. Present results nominate promising inactivation sources for severely resistant microorganisms, thereby paving the way toward sustainable disinfection systems.

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