Plastic pollution is one of the biggest global problems of our time.
Most people are familiar with the images of plastic bottles and bags floating in oceans or washed up on beaches.
Scientists have also been tracking microplastics—tiny pieces of plastic that are smaller than five millimeters—in animals, plants, and even the human body.
But an even bigger concern is emerging: nanoplastics.
These particles are thousands of times smaller than a human hair and can easily pass through barriers in the body, such as the skin or even the blood-brain barrier.
Detecting them has been extremely difficult, leaving researchers with large gaps in understanding how dangerous they may be.
Now, a team of scientists from the University of Stuttgart in Germany and the University of Melbourne in Australia has created a simple and affordable way to detect nanoplastics.
Their method uses a special color-changing test strip, called an “optical sieve,” that works with an ordinary optical microscope.
The study was recently published in Nature Photonics.
The new test strip makes nanoplastics visible by trapping them in tiny holes etched into a semiconductor surface.
When light shines on these holes, they reflect bright colors. If a plastic particle falls into one of the holes, the reflected color changes. By observing this change with a microscope, researchers can tell whether a particle is present and estimate its size.
“The test strip works like a sieve,” explained Ph.D. student Dominik Ludescher, the study’s first author. “Particles between 0.2 and 1 micrometer can be examined easily. The holes can be designed to match the size of the nanoplastics, and when they are filled, the color shift reveals their presence.”
Compared to current methods such as scanning electron microscopy, the new technique is far cheaper, requires no specialized training, and delivers results more quickly. That makes it an attractive option for widespread use in environmental and health research.
In their experiments, the researchers first worked with spherical nanoplastic particles of known sizes, mixing them into a lake water sample containing sand and organic material. The test strip was able to detect the number and size of nanoplastics in the sample at a concentration of 150 micrograms per milliliter.
The next step is to test more complex conditions, such as particles that are not perfectly spherical and mixtures of different types of plastic. The researchers also want to collaborate with other groups that can provide real-world water samples with known nanoplastic content.
In the future, the optical sieve could be developed into a portable strip that allows scientists—or even local authorities—to test water and soil samples directly in the field.
“This could be a simple tool for quickly measuring nanoplastics on site,” said Dr. Mario Hentschel, head of the Stuttgart Microstructure Laboratory.
If successful, this innovation could become an important part of the fight against plastic pollution, helping us better understand where nanoplastics are, how many there are, and what risks they pose to health and the environment.
