Microplastics are tiny, plastic fragments—many too small to see—found in the air, soil and water. Measuring their abundance in nature can direct cleanup resources, but current detection methods are slow, expensive or highly technical. Now, researchers publishing in ACS Sensors have developed a living sensor that attaches to plastic and produces green fluorescence. In an initial test on real-world water samples, the biosensor could easily detect environmentally relevant levels of microplastics.