Xu, W. et al. 2021. Reduction of SARS-CoV-2 Infectious Titers by Direct Contact with Cuprous-Oxide Impregnated Face Masks External Layers. RA Journal Of Applied Research. 7, 8 (Aug. 2021), 2471–2476. DOI:https://doi.org/10.47191/rajar/v7i8.01.