Following the beginning of the COVID-19 outbreak, lateral flow assays (LFAs)—the category of test strips in which the presence or lack of a pink line indicates whether a specific molecule, like a drug or a virus, has been detected—became household items. Yet despite their ubiquity and decades of development, there has not been a quantitative, physics-grounded method for explaining the sensitivity and limits of LFAs to help guide their design. ...read more read less