Nanoporous membrane filter cascade for size‐selective analysis of nano‐ and microplastic particles

Abstract

AbstractAnalytical routes for sampling and analysis of microplastic particles in the range of several 10 µm to 1000 µm are well established in environmental research. However, the current scientific efforts are targeting human health impact with an enhanced focus on nanoparticle analysis in drinking water, the food chain, and its disposition in the human body. A major challenge lies in the availability of cascade filter setups spanning several orders of magnitude down to 10 nm dimensions in a single filtration workflow allowing fast and reliable routines for size‐selective nano‐ and microplastic (NMP) particle analysis. In this work, we present a novel cascade filter system containing filters made of microporous Si (pore size >10 µm) and nanoporous Al2O3 (pore size 100 nm), thus realizing the corresponding NMP size selectivity. Inorganic filter materials are chosen due to their beneficial properties as substrates for NMP particle analysis, which are nonpolymer materials with high planarity for micro‐spectroscopy investigations. In our first experiments, we demonstrate the successful NMP size separation on Si and Al2O3 filter substrates. For this purpose, we implement a well‐defined NMP test material composed of a mixture of polyethylene terephthalate microplastic reference material and monodisperse nanoscale polystyrene particles. The NMP test material is applied in a laboratory filtration workflow for samples in liquid solution. Both filter stages are subsequently investigated with optical microscopy, electron microscopy (scanning electron microscopy), Raman spectroscopy, and scanning force microscopy (atomic force microscopy) to demonstrate their applicability as combined NMP particle analytic substrates. Here, we characterize the fundamental NMP properties such as particle shape, size, and spectroscopic fingerprints—optical and chemical—both qualitatively and quantitatively. Finally, requirements and limitations for a standardized NMP filtration and analytic workflow will be discussed.