Rapid COVID-19 tests are on the rise to deliver results faster to more people, and scientists need an easy, foolproof way to know that these tests work correctly and the results can be trusted. Nanoparticles that pass detection as the novel coronavirus could be just the ticket. Such coronavirus-like nanoparticles, developed by nanoengineers at the University of California San Diego, would serve as something called a positive control for COVID-19 tests.