When Associate Professor Mana Toma and her team at Institute of Science Tokyo set out to solve a growing problem, they built something surprisingly small to tackle something invisibly huge. Their new biosensor can detect tiny plastic particles floating in water—and it does the job in just 20 minutes.
Plastics in our rivers, lakes, and oceans don't stay large forever. Over time, they break into increasingly smaller pieces. The smallest of these, called nanoplastics, measure between 1 and 1,000 nanometers. To give that some perspective, a single human hair is about 80,000 nanometers wide. These particles have already been found inside human bodies, raising serious concerns about what they might be doing to our health.
The problem is that finding these particles has been incredibly difficult. Traditional methods like powerful microscopes and spectroscopy machines require expensive equipment, complicated preparation, and lots of time. That makes routine water testing impractical.
Toma's team took a different approach. They created a device that uses light to spot nanoplastics in water without needing complex steps first. At its core is a specialized protein fragment called a peptide, which was designed to stick specifically to polystyrene—one of the most common plastics found in everyday products. This peptide is attached to a thin gold film inside the sensor.
When water passes through the device, any polystyrene nanoparticles present grab onto the peptide. The sensor detects this binding using a technique called surface plasmon resonance, essentially watching how light behaves differently when plastic particles are present. The team can then calculate exactly how much plastic is in the sample.
In tests, the biosensor caught particles as tiny as 50 nanometers within 20 minutes. It worked in laboratory water that mimicked real freshwater, as well as in samples of aquarium water and pond water. The researchers reported a detection limit of 1.3 micrograms per milliliter.
"By simplifying the detection process, this biosensor could make nanoplastic monitoring more accessible than conventional methods that require specialized instruments and extensive sample preparation," Toma said.
The technology marks an important step toward making water safety testing more practical and widespread. While plastics continue to break down in the environment, tools like this one could help scientists track just how widespread the problem has become—and, eventually, measure whether cleanup efforts are actually working. Assistant Professor Shuo Cheng of the School of Environment and Society collaborated on the project, and the findings were published in the journal Biosensors and Bioelectronics.
For communities wondering what's in their water, faster answers may now be on the horizon.