With a grain of plastic : navigating the unvalidated territories of microplastic and nanoplastic analysis

The growing scientific and regulatory attention to microplastics (MPs) and nanoplastics (NPs) as emerging food contaminants has exposed major analytical challenges, driven by the need to characterize solid, heterogeneous, and polydisperse particles rather than dissolved molecules. Comprehensive analysis requires the reliable determination of particle number, size and shape distributions, and chemical composition. However, current methods remain limited in robustness and sensitivity, particularly at the nanoscale. A critical assessment of the field highlights key gaps, including the lack of harmonized validation criteria and quality assurance frameworks, the limited availability of high-throughput methods for large-scale monitoring, insufficient sensitivity for single-particle NP analysis, and the scarcity of representative reference materials. This thesis addresses these challenges through the development of multimodal analytical approaches for the detection and characterization of MPs and NPs. A high-throughput, automated fluorescence-based workflow for MP quantification in bottled water is developed – combining Nile Red staining, fluorescence microscopy, and AI-powered image analysis – and validated. The workflow is further extended by integrating single-particle atmospheric solids analysis probe mass spectrometry, enabling the determination of particle count, morphology, and chemical identity. At the nanoscale, a complementary workflow combining spatially confined hyper-concentration, fluorescence-guided localization, and infrared nanospectroscopy is introduced. This approach enables detailed characterization of NP morphology, composition, and surface chemistry, revealing localized oxidation and weathering patterns in NPs isolated from real samples.