Tea–Essential Oil–Metal Hybrid Nanocoatings for Bacterial and Viral Inactivation

Natural plant-derived antimicrobial nanocoatings have been synthesized by mixing brewed tea with cinnamaldehyde oil. Concurrent addition of copper or silver salts produces hybrid tea–cinnamaldehyde–copper or tea–cinnamaldehyde–silver nanocoatings, respectively. Tea–cinnamaldehyde, tea–cinnamaldehyde–copper, and tea–cinnamaldehyde–silver coatings are all found to display strong antibacterial efficacy against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus (Log10 Reduction = 8.44 and 7.90, respectively). Tea–cinnamaldehyde–copper and tea–cinnamaldehyde–silver hybrid nanocoatings deposited onto nonwoven polypropylene provide 98.6 and 99.8% deactivation, respectively, toward murine coronavirus MHV-A59 (a potential surrogate for COVID-19 global pandemic coronavirus SARS-CoV-2). Key advantages of this approach are that the coating fabrication involves just a single step, utilizes cheap reagents (which are widely available over the counter to the general public), does not require any equipment apart from a container, and the coatings spontaneously adhere to a variety of substrate materials (including silicon, glass, polyester, nonwoven polypropylene, poly(tetrafluoroethylene), and cotton). Tea is one of the most ubiquitous beverages in the world, meaning that these antimicrobial coatings could be produced locally almost anywhere and by anyone without the need for any specialized technical training or expertize (for example, at remote field hospitals during humanitarian crises and in low-income countries).