A joint research team from the University of Stuttgart in Germany and the University of Melbourne in Australia has developed a straightforward new method for detecting nanoplastics in environmental samples. The technique relies on an ordinary optical microscope and a specially designed test strip known as the “optical sieve.”
The findings, published in Nature Photonics, represent a potential breakthrough for environmental and health research. They offer an affordable alternative to costly and time-consuming analysis techniques.
Why nanoplastics are a growing concern
Plastic waste is among the most urgent environmental challenges of the 21st century. Attention has long focused on larger plastic debris and microplastics. Yet, scientists are increasingly concerned about nanoplastics. These are tiny fragments smaller than the width of a human hair.
These particles are formed as larger plastics break down and can cross biological barriers, including the skin and even the blood-brain barrier. Their small size makes detection extremely difficult, leaving major gaps in understanding their effects on human health and ecosystems.
A color-changing test strip
To tackle this challenge, the Stuttgart-Melbourne team created a test strip that uses light resonance effects in microscopic holes etched into a semiconductor substrate.
When viewed under an optical microscope, the holes display a bright color reflection. If a nanoplastic particle falls into one of these voids, the color changes, signaling its presence.
“Compared with conventional methods such as scanning electron microscopy, our new approach is far less expensive, requires no specialized training, and drastically reduces analysis time,” said Dr. Mario Hentschel, head of the Microstructure Laboratory at the University of Stuttgart.
How the optical sieve works
The method allows researchers to detect particles ranging from 0.2 to 1 micrometer. The sieve’s holes can be customized to capture specific particle sizes, while others are flushed away.
“If a particle is too large, it won’t fit into the void. If it’s too small, it washes out during cleaning,” explained Dominik Ludescher, PhD student and lead author of the paper. By designing test strips with voids of different sizes, scientists can determine not only the presence of nanoplastics but also their number, size, and size distribution.
Testing environmental samples
Because reference samples from natural waters with known nanoparticle concentrations are not yet available, the researchers created synthetic samples using lake water mixed with sand and organic matter. They added nanoplastic particles at known concentrations and successfully measured their presence and distribution using the optical sieve.
The team now plans to test irregularly shaped particles, distinguish different plastic types, and collaborate with groups experienced in analyzing real-world water samples.
Toward on-site environmental testing
The ultimate goal is to adapt the technology into a portable test strip for rapid, on-site analysis of water and soil samples. Researchers also envision applications in biomedical fields, where nanoplastics could be detected in blood or tissue.
“Our optical sieve could become a simple and mobile tool to monitor nanoplastic pollution and its impact on health,” said Professor Harald Giessen, head of the 4th Physics Institute at the University of Stuttgart.
The optical sieve represents a significant step toward making nanoplastic detection accessible, affordable, and scalable. As global concerns grow about plastic pollution’s effects on ecosystems and human health, such innovations could help close critical knowledge gaps and guide future policies.
