Rapid antigen tests can quickly and conveniently tell a person that they are positive for COVID-19. However, because antibody-based tests aren't very sensitive, they can fail to detect early infections with low viral loads. Now, researchers reporting in ACS Sensors have developed a rapid test that uses molecularly imprinted polymer nanoparticles, rather than antibodies, to detect SARS-CoV-2. The new test is more sensitive and works under more extreme conditions than antibody-based tests.