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Recognition of microplastics suspended in seawater via refractive index by Mueller matrix polarimetry
Summary
Researchers developed a method to identify microplastics suspended in seawater using Mueller matrix polarimetry, which measures how particles interact with polarized light. The study successfully classified different types of microplastics based on their refractive index, even for irregularly shaped particles with varying sizes, suggesting this approach could advance in-situ microplastic detection in ocean water.
Microplastics have become the marine pollution posing a human health risk, but they are difficult to be detected and recognized for different materials, irregular shapes, and broad size distributions. Microplastics' refractive index (RI) is related to the materials and can be characterized by the Mueller matrix. In this work, the particles are suspended in water and their Mueller matrices are measured by a particulate Mueller matrix polarimetry setup. Four kinds of spherical particles including microplastics are effectively classified by their Mueller matrices. Moreover, two kinds of common microplastics with broad size distributions, irregular shapes, and random orientations are also well recognized by the Mueller matrix. These results imply that RI plays a vital role in the recognition of microplastics suspended in water. By using the Mie theory and discrete dipole approximation simulation, the discussions explain in physics origin how RI affects Mueller matrix coupling with size and structure, and give some decoupling methods. Results in this work help advance future tools to in situ recognize the microplastics in seawater.