Green aspects, technical challenges and advances in optical determination of microplastics and nanoplastics using emerging nanomaterials

Microplastics and nanoplastics (M/NPs) are pervasive environmental contaminants that pose significant risks to ecosystems and human health through ingestion, bioaccumulation, and toxicity. Their ability to penetrate biological barriers and act as vectors for hazardous chemicals has intensified the demand for sensitive, rapid, and reliable analytical methodologies. Optical sensing techniques have gained considerable attention due to their high sensitivity, real-time response, minimal sample preparation, and potential for field-deployable analysis. This review provides a comprehensive overview of recent advances in the application of six emerging functional materials for optical M/NP detection: hydrophobic fluorophores, carbon quantum dots (CQDs), graphene-based materials, metallic nanoparticles (NPs), metal–organic frameworks (MOFs), and upconversion nanoparticles (UCNPs). Fluorophores enable rapid visualization through selective fluorescence staining, while CQDs offer tunable photoluminescence, excellent stability, and low toxicity. Metallic nanoparticles exploit localized surface plasmon resonance and surface-enhanced Raman spectroscopy (SERS) for enhanced sensitivity and molecular fingerprinting. MOFs provide high surface area and structural tunability for analyte preconcentration and selective recognition. Graphene-based materials serve as auxiliary platforms for adsorption, enrichment, and signal amplification, whereas UCNPs function primarily as tracking labels for mechanistic biodistribution studies. This review critically discusses sensing mechanisms, material design strategies, analytical performance, greenness considerations, and current limitations for each material class. Key challenges including matrix interference, lack of standardized protocols, limited real-sample validation, and reproducibility concerns are highlighted. Future perspectives emphasize integrating multifunctional materials, artificial intelligence-assisted analysis, and advanced optical techniques to enable more robust, selective, sustainable, and practically applicable monitoring of M/NPs in complex environmental matrices. This comprehensive analysis aims to guide the development of next-generation optical sensors for reliable M/NP monitoring.