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A Multispectral Pulsed-Transmission Laser-Diode Sensor Concept for Real-Time In Situ Assessment of Microplastics in Water
Summary
Scientists have designed a concept for a laser-based sensor that could detect and even identify types of microplastics directly in water, in real time — no lab testing or sample prep needed. This matters because current methods for finding microplastics are slow and require sending samples to a lab, making it hard to quickly monitor drinking water or other sources for these tiny plastic particles, which are increasingly linked to health concerns. It's important to note this is still a theoretical model, not yet tested on real water samples, so real-world validation is the next step.
Microplastic monitoring needs methods that operate directly in water with minimal sample handling. Conventional techniques such as infrared and Raman spectroscopy and pyrolysis-GC/MS provide polymer-specific information but require sample preparation and delayed laboratory analysis. We propose an optical sensor concept for real-time, in situ microplastic assessment, based on multispectral pulsed transmission in the visible range using synchronized laser-diode lines and the directly transmitted signal through an active sensor volume. After calibration on particle-free water, each particle event reduces to a water-normalized transmission whose deficit is set by geometrical beam-particle overlap and the wavelength-dependent extinction efficiency. The weak polymer absorption is represented by the Urbach-tail formalism, the refractive-index-related redirection of light by a Fresnel-based, surface- and orientation-averaged probability of direct transmission, and particle size and shape are decoupled through an effective optical length. The coupled nonlinear system is solved for the bounds of the polymer absorption coefficient per candidate geometry. Because each polymer occupies a bounded region in multi-wavelength absorption space fixed by its band gap and structural state, the method can, in principle, separate structural modifications of identical composition, such as low- and high-density polyethylene. This is a sensor concept with a model-based proof of concept, not full environmental validation. Experimental verification on real reference particles is reported separately; the present article establishes the measurement model and inversion scheme that this verification builds on.