Control of microbial agents by functionalization of commercial air filters with metal oxide particles

According to the World Health Organization, low-quality air results in 3.2 million premature annual deaths of which 21 % are attributed to respiratory infections. The recent coronavirus (COVID-19) pandemic, responsible for millions of deaths worldwide, has highlighted the issue of airborne pathogens on human health. Air filtration is an established method to ensure good indoor air quality, being effective at capturing airborne particles and dust, as well as pathogens, and preventing diseases such as asthma. Nevertheless, with usage, water from air humidity, dust, and dirt, including fungi and bacteria spores, can accumulate on filters creating ideal conditions for the propagation of microorganisms. Thus, the filter can become a secondary source for airborne pathogens. In this work, antiviral and antibacterial filters were prepared by spray coating Ag2O, CuO, and ZnO particles into commercially available air filters. The reliability of the filters was tested through particle release in air, through a scanning mobility particle sizer, and filtration performance was measured against an aerosol of iron nanoparticles in nitrogen gas produced through a spark discharge generator. Additionally, the biosafety of the filters was measured in vitro through cytotoxicity tests against L-929 mouse fibroblast cells. Antibacterial activity was measured in vitro against two clinically relevant pathogens: Streptococcus pneumoniae and Pseudomonas aeruginosa and the anti-viral performance was measured against human respiratory syncytial virus. In general, the results have shown that spray coating is a reliable solution, with no detectable cytotoxicity effects or particle release in the air. After functionalization, both Ag2O and CuO compounds have been shown to have total antiviral activity (over 99 %), while only Ag2O presented a clear antibacterial action. In conclusion, spray coating as postmanufacturing functionalization of air filters can be an efficient and low-cost solution against airborne pathogens.