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Raman Tweezers for micro and nanoplastics analysis in watery ecosystems
Summary
Raman Tweezers — instruments that combine laser trapping with Raman spectroscopy — were demonstrated as a powerful tool for identifying individual micro- and nanoplastic particles in water samples without physical contact. The technique can measure both the size and chemical composition of particles as small as nanometers, addressing a major gap in detection capabilities for nanoplastics. This analytical advance could enable more sensitive monitoring of the smallest plastic particles in aquatic environments.
Hybrid instruments combining Optical Tweezers (OT) with Raman spectroscopy (Raman Tweezers, RT) are becoming increasingly popular, as they enable measurements of size and composition of micro and nanoparticles in a contact-less fashion. RTs are gaining attention as a unique analytical tool for environmental sciences and food analysis, capable to detect and chemically identify micro- and nano-plastics (MNPs). Here we show optical trapping and chemical identification of sub-20 μm plastics, down to the 50 nm range by RT [1]. Analysis at the single particle level allows us to unambiguously discriminate plastics from organic matter and mineral sediments, overcoming the capacities of standard Raman spectroscopy in liquid, intrinsically limited to ensemble measurements. Applications are demonstrated on both model particles and naturally aged environmental samples, made of common plastic pollutants, including polyethylene, polypropylene, nylon, and polystyrene, also in the presence of a thin eco-corona. Finally the analysis is extended to samples of tire and road wear particles collected from a brake test platform, where we highlight the presence of sub-micrometric agglomerates of rubber and brake debris, thanks to the presence of additional spectral features other than carbon [2]. Either used to trap & analyse single particles or coupled to field-flow fractionation techniques, RT have the potential to fill the technological gap in MNP detection. In the next years research & development will be oriented towards the exploration of the full potential and limits of RT in terms of sensitivity, size limitations, multispectral analysis and chemical information that can be extracted from contaminated MNPs and in complex environments. [3] [1] Gillibert et al. Environ. Sci. Technol. 2019, 53, 15, 9003 [2] Gillibert et al. Environ. Sci.: Nano, 2022, 9, 145 [3] Volpe et al. Roadmap for Optical Tweezers, arXiv preprint arXiv:2206.13789 (2022) Also see: https://micro2022.sciencesconf.org/425821/document