Identification and visualisation of microplastics/nanoplastics by Raman imaging (i): Down to 100 nm

Abstract

While microplastics (1 μm–5 mm) contamination is creating public concern, nanoplastics (<1000 nm) might create even more serious environmental contamination issues. This is likely due to the smaller size/higher specific surface area of nanoplastics which works more efficiently as a vector for other contaminants’ transportation and fate, to release the formulation additives and to be accumulated in the human body. The research on nanoplastics is currently hampered by the absence of an effective characterisation method, although X-ray photoelectron spectroscopy/Scanning Electron Microscopy (XPS/SEM) is reportedly dominating the nanoplastics characterisation approaches. Recently, imaging technology, which provides direct visualisation of the targets, is attracting increased attention. In this study, we demonstrate that Raman imaging can be employed to visualise and identify microplastics and nanoplastics down to 100 nm, by distinguishing the laser spot, the pixel size/image resolution, the nanoplastics size/position (within a laser spot), the Raman signal intensity, and via the sample preparation etc. We also validate this technique for the analysis of paint-polishing dust samples that have been collected from a driveway when a vehicle’s clear coating of poly-acrylic was polished by hand. We estimate that billions-trillions of microplastics/nanoplastics ranging from ∼7 μm down to ∼200 nm have been generated by hand-polishing an engine hood.