Optical microscopic methods for testing face mask efficacy for COVID-19

COVID-19 has spread worldwide and it is leaving everyone wondering how to protect themselves or to help those who are affected. Furthermore, the increased number of infectious diseases has become a significant health concern over recent decades. The respiratory droplets or airborne route, one of the transmission methods, impact social relationships significantly and can be avoided by using a face mask. Face masks are available in a variety of degrees of protection. Even in the face of the ongoing pandemic, individuals made their masks from household items due to the lack of face masks worldwide. In developing countries, surgical masks (SMs) and cloth masks (CMs) made of various cloth materials are very common. These types of masks are typically used for months after being repeatedly washed and dried. However, there is no indication of how washing, drying, or stretching practices affect the quality of CMs and SMs. Various efforts have been devoted for making effective face masks by using antimicrobial activity and super-hydrophobicity. This review article aims to discuss the mask efficiency of commercial SMs and homemade CMs from the public health and technical perspective. Recent advancements in mask engineering, disinfection, and material science have also been discussed. Optical microscopic methods were employed to assess the efficiency of different face masks and determine the quality of masks after washing, drying, and stretching. The filtration efficiency of CMs ranges from 63% to 84%. However, the SM had the highest filtering effectiveness and efficiency of 94%.