SARS-CoV-2 and approaches for a testing and diagnostic strategy.

The COVID-19 pandemic has led to an unprecedented global health challenge, creating sudden, massive demands for diagnostic testing, treatment, therapies, and vaccines. In particular, the development of diagnostic assays for SARS-CoV-2 has been pursued as they are needed for quarantine, disease surveillance, and patient treatment. One of the major lessons the pandemic highlighted was the need for fast, cheap, scalable and reliable diagnostic methods, such as paper-based assays. Furthermore, it has previously been suggested that paper-based tests may be more suitable for settings with lower resource availability and may help alleviate some supply chain challenges which arose during the COVID-19 pandemic. Therefore, we explore how such devices may fit in a comprehensive diagnostic strategy and how some of the challenges to the technology, e.g. low sensitivity, may be addressed. We discuss the properties of the SARS-CoV-2 virus itself, the COVID-19 disease pathway, and the immune response. We then describe the different diagnostic strategies that have been pursued, focusing on molecular strategies for viral genetic material, antigen tests, and serological assays, and innovations for improving the diagnostic sensitivity and capabilities. Finally, we discuss pressing issues for the future, and what needs to be addressed for the ongoing pandemic and future outbreaks.

Developing a Paper-Based Antigen Assay to Differentiate between Coronaviruses and SARS-CoV-2 Spike Variants.

COVID-19 first appeared in December of 2019 in Wuhan, China. Since then, it has become a global pandemic. A robust and scalable diagnostics strategy is crucial for containing and monitoring the pandemic. RT-PCR is a known, reliable method for COVID-19 diagnostics, which can differentiate between SARS-CoV-2 and other viruses. However, PCR is location-dependent, time-consuming, and relatively expensive. Thus, there is a need for a more flexible method, which may be produced in an off-the-shelf format and distributed more widely. Paper-based immunoassays can fulfill this function. Here, we present the first steps toward a paper-based test, which can differentiate between different spike proteins of various coronaviruses, SARS-CoV-1, SARS-CoV-2, and CoV-HKU1, with negligible cross-reactivity for HCoV-OC43 and HCoV-229E in a single assay, which takes less than 30 min. Furthermore, our test can distinguish between fractions of the same spike protein. This is done by an altered assay design with four test line locations where each antigen builds a unique, identifiable binding pattern. The effect of several factors, such as running media, immunoprobe concentration, and antigen interference, is considered. We find that running media has a significant effect on the final binding pattern where human saliva provides results while human serum leads to the lowest signal quality.