Session VR1: Plasma Sterilization and Disinfection: Research and Development Efforts Relevant to the Fight Against COVID 19 and Future Microbial Outbreaks

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Reactive oxygen species inactivate viruses in a dose-dependent fashion. For example, hydrogen peroxide (H2O2) can reduce SARS-CoV-2 on abiotic surfaces by 4-6 logs of plague-forming unit (PFU) per mil in 1 min. There are also evidences that viruses are vulnerable to ROS-generating agents such as cold atmospheric plasma (CAP). To gain specific insight, we studied whether a surface cold atmospheric plasma (CAP) and its activated water may inactivate bacteriophages, viruses that infect bacteria, as surrogates of human viruses. We considered three types of bacteriophages, namely T4, F174 and MS2 that have different nuclear acids, namely double-stranded DNA (T4), single-stranded DNA (F174), and RNS (MS2). Incubation with CAP for 60 s or with PAS for 80 s led to ~10 log PFU/ml) reduction of F174 and MS2 were reduced by ~10 logs of PFU/ml by 60 s-CAP or 80 s-PAS treatment, both with 1-h incubation post treatment, whereas 10-log reduction of T4 required a longer treatment of CAP or PAS. Experiments using ROS reconstitution and scavenging identified singlet oxygen as a major player. Further, DNA and protein analysis of T4 bacteriophages found (1) DNA and protein damage of virus that limit their replication; and (2) aggregation of bacteriophages that compromise their propagation (Fig. 1). Together, these data suggest that CAP and PAS are active in coronaviruses and may be further improved with its antiviral mechanism.\\ \\L. Guo, R. Xu, L. Guo, Z. Liu, Y. Zhao, D. Liu, L. Zhang, HL Chen, MG Kong. Appl. Environ Microbiol. 84, e00726-18 (2018).\\ \\In collaboration with: l. Guo, State Key Lab Electrical Insulation and Power Equipment, Center for Plasma Biomedicine, Xi'an Jiaotong University Xi'an, People's Republic of China; H. L. Chen, Frank Reidy Center for Bioelectrics, Old Dominion University, Norfolk, USA   

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The COVID-19 pandemic is caused by the coronavirus SARS-CoV-2, which can spread through the air via respiratory droplets and aerosols, as well as fomites on contaminated surfaces. The high risk of airborne transmission of SARS-CoV-2 via respiratory droplets led to an increased demand and eventual shortage of N95 masks and other personal protective equipment (PPE) needed by medical professionals on the frontlines of the pandemic. Although respiratory droplets (on the order of 100 microns) can settle from the air relatively quickly, respiratory aerosols (<10 microns) that could contain virus particles can remain airborne for long distances and durations. This talk will describe two on-going efforts at C&J Nyheim Plasma Institute at Drexel University related to the rapid development of non-equilibrium plasma technologies to combat the COVID-19 pandemic. The first effort involves the development of a non-equilibrium short pulsed plasma system that can generate plasma activated fog that is capable of rapid decontamination of PPE. Current results show that greater than 99.9% percent inactivation of viruses is achievable on N95 masks and that the filtration efficiency of the masks is not significantly affected after 20 treatment cycles. The second effort involves a device designed for direct airborne treatment of aerosol droplets containing viral particles using short pulse plasmas. Early results of this technology for direct plasma treatment of air indicates rapid inactivation of enveloped and non-enveloped viruses is achievable under high air flow rates.   

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Increasing recognition of the transmissibility of the SARS-CoV-2 virus between humans as airborne aerosols, and the limited options for respiratory protection against such transmission, have drawn attention to air purification products, with their relative advantages and disadvantages being closely considered. This presentation reviews recent experimental achievements in using non-thermal plasmas (NTPs) as an improvement upon HEPA filtration and ultraviolet irradiation for rapid inactivation of airborne viruses of the sort that is essential for the treatment of flowing air streams typical of ventilation systems. Studies considering both viral surrogates and actual viral pathogens known to cause animal disease are discussed. Particular challenges in conducting inactivation studies of viral aerosols are enumerated and current solutions described. Finally, performance comparisons between NTP air sterilization and the established technologies of UV irradiation and particle filtration are presented, showing the substantial promise for performance improvements that NTP approaches offer.   

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Atmospheric pressure plasmas are a source of a range of reactive species, UV light, and charge that has the capacity to destroy bacteria and viral particles. The destruction pathways include mechanical or chemical destruction of the outer protective envelope or genetic material damage. Here we present the capacity of a plasma tool called the plasma wand to deliver oxidative stress to surfaces for the purpose of sterilization. Delivery of hydrogen peroxide and ozone is quantified along with the production of reactive nitrogen species using chemical probes and physical targets. The effect of these species on E-Coli colonies is also ascertained. Preparation for MS2 phage as a surrogate virus is described. Implications for the treatment of COVID-19 virus is discussed along with a review of diagnostic tools required to access efficacy. This latter point is generally applicable to all plasma based sterilizers and thus serves as general guidance for accessing decontamination.