Singapore scientists develop reusable mask that filters 99.9% of bacteria, viruses, and haze The filter of the NTU-developed mask is coated with a layer of copper oxide nanoparticles. PHOTO: NTU The Straits Times The Straits Times Scientists from the Nanyang Technological University (NTU) have developed a reusable mask that is able to kill bacteria droplets within 45 seconds and filter 99.9 percent of bacteria, viruses and haze particles - better than the medical-grade N95 masks used in hospitals. N95 masks are able to prevent around 95 percent of aerosolised droplets and particulate matter of around 0.3 microns in size from entering them. The filter of the NTU-developed mask is coated with a layer of copper oxide nanoparticles, which damage the DNA of important cell structures in the bacteria, causing them to die, said Professor Lam Yeng Ming, chair of NTU's School of Materials Science and Engineering, who developed the antimicrobial coating.