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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 small, waterproof camera system that can be dropped directly into streams to detect and identify different types of microplastic pollution in real time, correctly sorting plastic types about 99% of the time even in murky, unfiltered water. This matters because faster, cheaper field testing could help researchers track how much plastic pollution is entering our water sources — an important step toward understanding potential risks to drinking water and human health, since we still don't fully know how microplastics affect our bodies.
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.