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New test strip makes invisible nanoplastics visible
Nanoplastic particles made visible: the newly developed test strip from the University of Stuttgart allows dangerous nanoplastic particles to be detected under a light microscope. Credit: University of Stuttgart / 4th Physics Institute
Researchers at the University of Stuttgart, in collaboration with the University of Melbourne, have developed an inexpensive optical test strip — an "optical sieve" — that reveals nanoplastic particles using a standard light microscope. Reported in Nature Photonics, the technique uses engineered microscopic holes in a semiconductor substrate that change color when a particle lodges inside, enabling visual detection, counting, and size estimation of particles down to submicrometer scales.
How the optical sieve works
The optical sieve exploits resonant optical effects in tiny depressions called Mie voids. Each void reflects a characteristic bright color depending on diameter and depth; when a nanoplastic particle enters the void, the reflected color shifts. By patterning arrays of voids of different sizes, the strip functions like a sieve: particles of matching size preferentially collect in the corresponding holes, producing a color map that reveals presence, number, and approximate size distribution.
The optical sieve nanoplastic particles fall into holes of the appropriate size in the test strip. The color of the holes changes. The new color provides information about the size and number of particles. Credit: University of Stuttgart / 4th Physics Institute
Advantages and experimental validation
Compared with scanning electron microscopy, this approach is far less expensive, faster, and simpler to operate, reducing reliance on specialized instruments and personnel. In laboratory tests the team added known quantities of spherical nanoparticles to lake water containing sand and organic matter, then used the optical sieve to measure a sample concentration (150 µg/ml) and determine size distribution.
Detection range and limitations
Current demonstrations reliably resolve particles roughly 0.2–1 µm in diameter. The researchers plan further work to test non-spherical particles, differentiate polymer types, and validate the method on environmental samples with naturally occurring nanoplastic mixtures.
Implications for environmental and health monitoring
Nanoplastics are a growing concern because their sub-micrometer size allows them to cross biological barriers, potentially reaching tissues and organs. A low-cost, field-deployable optical sieve could enable on-site screening of water, soil, or even biological fluids, accelerating environmental surveys and supporting toxicological studies.
Conclusion
The optical sieve is a promising, scalable tool for nanoplastic detection that complements existing microscopy and chemical analysis methods. With further validation on real-world samples and advances in material discrimination, it could become a practical frontline assay for researchers and monitoring programs.
Source: scitechdaily
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