HEPA filters were coated with charged carbon nanotubes. During the filtration study, the nanotubes were shown to be 92% effective in the filtration of a viral bacteriophage, MS2, as a model of viral particle [158]. There are virtually no reports on coated antiviral air filters, let alone employing an LbL coating method to create these masks. These are rapid inactivation action, broad-spectrum inactivation not only against specific strains, and lastly universal application on various media, not just facial masks [159].