| Bioaerosol exposure has caused numerous adverse health effects includingpulmonary impairments, allergic diseases, toxic reactions as well as sick buildingsyndrome. In recent years, the number of people with allergic diseases is increasingand airborne pandemic influenza outbreaks occurred frequently. Most recently, SARSalike virus surfaced again and another new virus H7N9was transmitted from birds tohumans, and all these serve as a wakeup call for another influenza pandemic. Inaddition, the threat of bioterrorism is also increasing due to regional instability. It ishighly important to develop effective measures to block the outbreak of diseases.However, current bioaerosol inactivation technologies face the challenges in meetingthe efficiencies, applicability and environment-safety.This study was carried out to investigate the effects and relevant mechanisms ofmicrowave irradiation (thermal effect) and cold plasma (non-thermal effect) onviability and allergenicity of bioaerosols. In this study, both lab-generated andenvironmental bioaerosols were exposed to microwave irradiation and cold plasma forvarying time intervals at different output power levels, collected by a biosampler andthen analyzed using various biochemical analysis methods. Traditional culturemethods and enzyme-linked immunosorbent assay were used to investigate theviability of bacterial, fungal and viral aerosols, and the allergenicity of allergenaerosols, respectively. To investigate the relevant mechanisms, experiments involvingliquid-borne exposure of these species were also conducted. In addition, DNA stain aswell as polymerase chain reaction coupled with ethidium monoazide (EMA-qPCR)methods were used to study the viability of bacterial aerosols; scanning electronmicroscope (SEM) and transmission electron microscope (TEM) were applied toinvestigate the membrane surface morphologies and intracellular components ofmicrobes and the structure of allergens; polymerase chain reaction-denaturinggradient gel electrophoresis (PCR-DGGE) method was used to study the diversitylosses and possible gene mutation of bacterial aerosols; agarose gel electrophoresis combined with reverse transcription polymerase chain reaction (RT-PCR) was utilizedto study the effects of microwave irradiation and cold plasma on viral RNA genescoding for proteins.The results of this study showed that direct exposure to microwave irradiation at700W for about1.5minutes resulted in more than90%inactivation of both airbornePseudomonas uorescens and bacteriophage MS2, while exposure to cold plasma at24W for about0.12s resulted in100%inactivation of airborne Pseudomonasuorescens and85%of bacteriophage MS2, respectively. In addition to theinactivation of lab generated bioaerosols, microwave irradiation and cold plasma werefound to significantly inactivate the environmental bacterial and fungal aerosols. Forexample, exposure to cold plasma for about0.06s resulted in96%inactivation ofairborne bacteria and87%of fungi. Moreover, cold plasma was also found to reducesignificantly the allergenicity of various airborne allergens, eliminating81%of canineallergen Can f1in0.06s. Compared to current air cleaning technologies, microwaveirradiation offers a simple, practical, broad-spectrum and non-invasivedecontamination technology, while cold plasma provides a fast and high-efficiency airpurification technology which broke through the bottleneck of conventionaltechniques in inactivation time and efficiency.The exact inactivation mechanisms of microwave irradiation and cold plasma arestill under debate. Based on the results obtained in this study, it was possible that themicrobial inactivation by microwave irradiation is a result of both thermal andnon-thermal effects which together caused damages to membrane surfacemorphologies, intracellular components and genes; while the inactivation effects ofcold plasma are caused by chemical components such as OH species and antozone,and the charged particles, which destroyed the cellular structure and genetic integrity.The results also revealed the elementary inactivation mechanisms of microwaveirradiation and cold plasma on virus: exposure to microwave irradiation and coldplasma caused evident damage to viral RNA genes coding for A protein andreplication enzyme, thereby resulting in the loss of the viral ability to express theprotein and thus the ability to identify the host and further replicate.Compared to previous studies, this work proposed a new method of usingmicrowave irradiation to directly inactivate bioaerosols. With systematic investigationon the effects of microwave irradiation and cold plasma on airborne bacteria, fungi,viruses and allergens, this study provided valuable references for developing relevantinactivation technologies for reducing infections and allergies. Results from this workhave great potential to be utilized in sterilizing air for closed or semi-closedenvironments such as central air conditioning system, hospitals, flight cabin as well as military bases. In particular, exposure to microwave irradiation and cold plasmaresulted in more than90%inactivation of airborne virus, holding great promise incontrolling the airborne transmission of virus, such as SARS virus and influenzaviruses, and preventing large-scale outbreaks of diseases. |
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