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.

Currently, scientists detect microplastics in water samples using microscopes or analytical tools, such as infrared or Raman spectroscopy. While these techniques are accurate, they require multiple steps to prepare samples before analysis and can be expensive and time-consuming. In a step toward a simpler method, Song Lin Chua and colleagues created a living microplastics sensor from the bacterium Pseudomonas aeruginosa. This bacterium is commonly found in the environment and can naturally establish biofilms on plastic materials, though some strains are opportunistic human pathogens. The team wanted to modify the bacterium slightly to create a living sensor that easily detects microplastics in water samples.

The researchers added two genes to a non-infectious laboratory strain of P. aeruginosa to make the sensor. One gene produces a protein that activates when bacterial cells contact plastic, and the other gene produces a green-fluorescent protein in response. In lab tests, the engineered bacteria fluoresced in vials containing plastic pieces and a growth medium, but not in separate vials of other materials such as glass and sand.

A measurable fluorescence was produced within 3 hours for various plastics, including polyethylene terephthalate (recycling symbol 1) and polystyrene (recycling symbol 6). Additionally, the modified bacterial cells stayed active for up to 3 days in the refrigerator (39 degrees Fahrenheit, 4 degrees Celsius), which the researchers say indicates it could be transported to field locations.

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To test the living microplastics sensor as an environmental monitoring tool, the researchers added the engineered P. aeruginosa to seawater from a city waterway. The seawater was first filtered and then treated to remove organic matter before the bacteria were added. Based on the fluorescence intensity values, the water samples contained up to 100 parts per million of microplastics. Further water analysis with Raman microspectroscopy revealed that the microplastics were primarily biodegradable types, such as polyacrylamide, polycaprolactone and methyl cellulose, which the biosensor detected despite the initial tests being done on traditional polymers.

“Our biosensor offers a fast, affordable and sensitive way to detect microplastics in environmental samples within hours,” says Chua. “By acting as a rapid screening tool, it could transform large-scale monitoring efforts and help pinpoint pollution hotspots for more detailed analysis.”