Nanoplastic Analysis by On-line Coupling of Raman Microscopy and Field-Flow Fractionation Enabled by Optical Tweezers

Christian Schwaferts, Vanessa Sogne, Roland Welz, Florian Meier, Thorsten Klein, Reinhard Niessner, Martin Elsner, Natalia P. Ivleva

Nanoplastic pollution is of emerging environmental concern, but current analytical approaches are facing limitations in this size range. However, the coupling of nanoparticle separation with chemical characterization bears potential to close this gap. Here, we realize the hyphenation of particle separation / characterization (field-flow fractionation (FFF), UV and multi angle light scattering (MALS)) with subsequent chemical identification by on-line Raman microspectroscopy (RM). The problem of low Raman scattering was overcome by trapping particles with 2D optical tweezers. This setup enabled RM to identify particles of different materials (polymers and inorganic) in the size range from 200 nm to 5 µm, with concentrations in the order of 1 mg/L (109 particles L-1). The hyphenation was realized for asymmetric flow FFF (AF4) and centrif-ugal FFF (CF3), which separate particles based on different properties. This technique shows potential for application in nanoplastic analysis, as well as many other fields of nanomaterials.

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