From laboratory to field: A review of portable Raman spectroscopy for real-time microplastic monitoring in aquatic environments.

Microplastics and nanoplastics are recognized as persistent pollutants in aquatic environments, posing ecological and toxicological risks across trophic levels. However, their detection remains analytically challenging. Conventional laboratory-based techniques - Fourier-transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, and pyrolysis-gas chromatography-mass spectrometry - provide detailed characterization but are constrained by extensive sample preparation, long analysis times, and high contamination risks during sample handling. To overcome these limitations, portable Raman spectroscopy has emerged as a promising approach for in situ MPs detection, enabling direct and rapid identification in aqueous environments. However, a systematic review of the current literature reveals that most applications employing portable Raman instruments still rely on laboratory-based pre-treatment steps, including filtration and artificial spiking of samples, limiting field portability and their real-time analytical potential. Notably, only one study conducted direct in situ field measurements using a portable Raman device. However, even in that case, a filtration step was integrated into the portable setup, introducing potential contamination and undermining the goal of fully field-deployable operation. The reliance on pre-treatments highlights a gap between the promise of portability and its real-world applicability. In response, this review systematically examines recent advances in portable Raman-based detection of MPs and NPs, identifies methodological and instrumental constrains hindering true in situ analysis, while showcasing promising innovations that could enable real-time measurements in liquid matrices. Progress toward fully integrated, contamination-free portable systems will be essential to bridge laboratory-based innovation and on-site monitoring, ultimately facilitating faster and more reliable assessment of plastic pollution in aquatic ecosystems.