Existing antibody-based tests for infectious diseases such as malaria are fairly cheap, but even a dollar per test can be prohibitively expensive if the target population comprises millions of people in the world's poorest countries. Now a better screening tool is coming to the fore: mass spectrometry, a common chemistry tool that precisely identifies molecules on the basis of their atomic weight. A portable machine built at Johns Hopkins University is more sensitive than antibody-based tests, covers all four kinds of malaria, and costs very little to operate.

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