The project, funded by the German Federal Environmental Foundation (DBU) under reference 37730/01‑23, developed an innovative cascade filtration system for the detection and analysis of micro‑ and nanoplastics (MNP) in environmental and toxicological samples. The system is designed to capture particles ranging from larger than 5 µm down to below 100 nm, a range that is critical for monitoring emerging contaminants in drinking water and other media.

The technical work focused on the design of a multi‑stage filter layout and the fabrication of silicon‑based filter substrates with precisely controlled pore geometries. Laser ablation was first used to pre‑structure the silicon surface, creating a pattern of pits that served as nucleation sites for subsequent photo‑electrochemical etching. The etching process, carried out in a custom reactor equipped with a light source, produced pores with diameters from 1 µm to 10 µm and a membrane thickness of 500 µm. In addition, laser drilling was employed to create larger pores (up to 50 µm) with a spacing of 150 µm, enabling the capture of larger microplastic fractions. Silicon nitride (SiN) masks were applied to refine the pore distribution and improve uniformity.

Performance testing involved filtering aqueous suspensions of polyethylene terephthalate (PET), polystyrene (PS), and poly(methyl methacrylate) (PMMA) particles of known size distributions. Scanning electron microscopy (SEM) confirmed the retention of particles above the designed cut‑off sizes, while micro‑Raman spectroscopy and atomic force microscopy (AFM) verified the presence of nanoplastic fragments on the filter surfaces. Raman mapping revealed a photo‑electrochemical signal an order of magnitude stronger than the substrate background, indicating successful functionalization of the filter material. The cascade arrangement allowed selective enrichment of distinct size classes, with the first stage capturing particles >5 µm, the second stage retaining 1–5 µm particles, and the final stage concentrating sub‑100 nm fragments.

To integrate the filters into routine laboratory workflows, a custom adapter was fabricated for the Sartorius funnel system. The adapter, comprising a plate, cup, O‑ring, and a second‑stage filter holder, ensured a tight seal and facilitated easy replacement of filter stages. This modular design enables rapid throughput and compatibility with existing analytical instruments.

The project was carried out in collaboration between SmartMembranes GmbH, which led the design and fabrication of the filter substrates; the Martin‑Luther University Halle‑Wittenberg, which provided academic expertise in materials science and analytical chemistry; Fraunhofer Center for Surface Physics (CSP), which contributed advanced surface characterization; and the Federal Institute for Materials Research and Testing (BAM), which performed independent validation of filtration performance. The research spanned from early 2023 through October 2024, culminating in the final report dated 28 October 2024.

In summary, the project achieved a scalable, high‑resolution filtration platform capable of separating micro‑ and nanoplastics across a broad size spectrum. The combination of laser‑based structuring, photo‑electrochemical etching, and rigorous analytical validation demonstrates the feasibility of deploying such cascade filters for environmental monitoring and toxicological assessment, thereby supporting the European Union’s drinking‑water directive and emerging regulatory frameworks for plastic pollution.