STUTTGART/MELBOURNE, 8 September 2025 — A joint research team from the University of Stuttgart (Germany) and the University of Melbourne (Australia) has developed a simple, affordable method for detecting nanoplastics in environmental samples. Using only a standard optical microscope and a specially designed test strip—the “optical sieve”—scientists can now visualize and analyze particles that were previously invisible without expensive, high-tech equipment. The breakthrough has been published in Nature Photonics (doi: 10.1038/s41566-025-01733-x).

“The test strip can serve as a simple analysis tool in environmental and health research,” said Prof. Harald Giessen, Head of the 4th Physics Institute, University of Stuttgart. “In the near future, we aim to measure nanoplastic concentrations directly on site. The method may even be adapted to test blood or tissue samples for nanoplastics.”

Nanoplastics: An Invisible Threat

Plastic pollution is one of the most urgent global challenges of the 21st century. While microplastics have already been detected in oceans, rivers, and living organisms, scientists warn of an even greater danger—nanoplastics, particles smaller than a micrometer that can penetrate biological barriers such as skin and the blood-brain barrier. Detecting these particles has been a longstanding challenge, limiting our understanding of their risks to ecosystems and human health.

Color Changes Make the Invisible Visible

The new optical sieve provides a fast, cost-effective solution. Based on tiny etched depressions called Mie voids, the test strip uses light resonance effects to generate bright color reflections. When a nanoplastic particle falls into one of the voids, the reflected color shifts, making the particle visible under an ordinary optical microscope.

“Compared with conventional methods such as scanning electron microscopy, our approach is cheaper, faster, and doesn’t require highly trained personnel,” explained Dr. Mario Hentschel, Head of the Microstructure Laboratory at the 4th Physics Institute.

Particles between 0.2 and 1 µm in size can be detected and analyzed. By tailoring the void size, the sieve not only reveals whether particles are present but also allows determination of their number, size, and size distribution.

Proof of Concept with Synthetic Samples

To test the method, the team created water samples containing sand, organic material, and known quantities of spherical plastic nanoparticles. Even at concentrations as low as 150 µg/ml, the optical sieve successfully identified and sized nanoplastics, proving its potential as a practical monitoring tool.

Toward Real-World Applications

The researchers envision the optical sieve being used much like a test strip for on-site analysis of nanoplastics in water or soil. Future work will focus on detecting irregularly shaped particles, distinguishing between different types of plastics, and applying the method to real environmental samples.

“The test strip works like a classic sieve,” said first author Dominik Ludescher, PhD student at the University of Stuttgart. “By adapting the void sizes, we can selectively capture particles and identify them through their color signature.”

Original Publication
Authors: D. Ludescher, L. Wesemann, J. Schwab, J. Karst, S. B. Sulejman, M. Ubl, B. O. Clarke, A. Roberts, H. Giessen and M. Hentschel.
Journal: Nature Photonics
DOI: 10.1038/s41566-025-01733-x
Article Title: Optical sieve for nanoplastic detection, sizing and counting
Article Publication Date: 8-Sep-2025

Original Source: https://www.nature.com/articles/s41566-025-01733-x

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