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Classification of microplastics in field-collected stream water using a submersible single-shot lensless polarimetric holographic system
Summary
Scientists built a compact, waterproof camera-like device that can be dropped directly into streams to detect and identify different types of microplastic pollution in real time, without needing to collect samples and bring them back to a lab. In tests using real (unfiltered) stream water, the tool correctly identified the type of plastic about 99% of the time, which could make it much faster and easier to track where microplastic pollution is coming from and how much is in our waterways, an important step since these plastics can end up in the water we drink and the fish we eat.
Microplastic pollution in aquatic environments demands field-ready tools that can rapidly detect and discriminate particles in complex aquatic environments. Here, we present a single-shot polarimetric off-axis lensless holographic imaging system integrated into a compact submersible prototype. The system combines a simple off-axis interferometric layout, requiring only one mirror and one beam splitter, with a division-of-focal-plane (DoFP) polarimetric sensor to acquire four polarization-resolved holograms per exposure, enabling Fourier-domain order isolation and complex-field recovery while preserving polarization-dependent contrast. We validate joint phase and polarimetric reconstruction using a birefringent USAF resolution target and demonstrate polymer discrimination directly from raw four-channel hologram patches using a lightweight detection-classification pipeline (no phase reconstruction or handcrafted features), achieving approximately 99% test accuracy across four different polymers. Finally, submerged experiments in unfiltered, field-collected stream water with controlled microplastic spiking confirm accurate detection and time-resolved classification under realistic conditions.