Emerging Analytical Methodologies for Micro- and Nano-Plastics Detection in Human Samples: Analytical Challenges and...

Micro- and nanoplastics (MNPs) are increasingly detected in human tissues and biofluids, raising concerns about their potential health impacts. Yet, despite growing evidence of human exposure, reliable characterization of these particles remains a major analytical challenge. This review critically evaluates sample-preparation strategies, detection methodologies, and toxicological evidence for MNPs in human biological samples. MNPs have been detected across major human organ systems and biofluids. Sample preparation strongly affects MNP analytical accuracy and inter-study comparability; harsh digestion reduces matrix interference but may degrade polymers, whereas milder treatments preserve particles but leave organic residues. These methodological tradeoffs contribute substantially to variability among studies and complicate cross-study comparisons. Although experimental evidence indicates that particles smaller than 10 µm can induce oxidative stress, inflammation, and cellular dysfunction, current epidemiological evidence linking MNP exposure to human disease remains largely correlational. Comparative assessment of microscopy-based approaches, vibrational spectroscopy, and pyrolysis-gas chromatography-mass spectrometry reveals that no single analytical technique can simultaneously provide accurate particle sizing, polymer identification, and mass quantification. We highlight critical limitations of various techniques, including quantification, morphological information, resolution, and the potential for false-positive polymer assignments arising from sample preparation methodologies, residual biological matrices, and their pyrolysis products. Furthermore, nanoplastics, the fraction considered most biologically relevant, remain severely under-quantified because their dimensions fall below the practical detection limits of most routine analytical methods. Standardized protocols, certified reference materials, validated nanoplastic detection methods, and integrated multi-analytical detection strategies are urgently needed to advance reliable MNPs biomonitoring, improve inter-study comparability, and establish robust exposure-risk assessments.