20 minutes: That’s how long it takes a new paper-based test to identify the Zika virus. Researchers at MIT were facing a tricky problem: The best way to test for Zika (measuring viral RNA in the blood) is neither cheap nor portable. That made it hard for doctors to know who was infected in developing countries, like Mexico, Colombia, India, and Brazil. Other tests, meanwhile, are prone to false positives, since Zika is genetically similar to viruses such as dengue fever. So researchers devised a way to attach specific antibodies to strips of paper coated with nanoparticles. If sample blood placed on the paper strips contains a specific viral protein, then a colored spot appears, indicating a positive test. Researchers also found that their technique could distinguish between the four types of dengue fever, even if Zika wasn’t present — a useful diagnostic tool for doctors in its own right.Alex Kingsbury can be reached at email@example.com.