Selective imaging of microplastic and organic particles in flow by multimodal coherent anti-Stokes Raman scattering and two-photon excited autofluorescence analysis

Abstract

Microplastic pollution is an urgent global issue. While spectroscopic techniques have been widely used for identification of plastics collected from aquatic environments, these techniques are often labour-intensive and time-consuming due to sample collection, preparation and long measurement times. In this study, a method for two-dimensional detection and classification of flowing microplastic and organic particles with high spatial and temporal resolutions has been proposed based on simultaneous detection of coherent anti-Stokes Raman scattering (CARS) and two-photon excited autofluorescence (TPEAF) signals. Poly(methyl methacrylate) (PMMA), polystyrene (PS), and low-density polyethylene (LDPE) particles with the size of several tens to hundreds of µm were selectively detected in flow with an average velocity of 4.17 mm/s by CARS line scanning. With the same velocity of flow, flowing PMMA and alga particles were measured using a multimodal system of CARS and TPEAF signals. The average intensity of both PMMA and alga particles in the CARS signals at the frequency of 2940 cm−1 were higher than the background level, while only algae emit TPEAF signals. Therefore, classification of PMMA and alga particles in flow has been successfully performed by simultaneous detection of CARS and TPEAF signals. With the proposed method, monitoring of microplastics in continuous water flow without collection or extraction is possible, which is game-changing for current sampling-based microplastic analysis.

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Identifiers

ORCID for Konstantinos Bourdakos: orcid.org/0000-0003-2737-5657

ORCID for James Arthur Read: orcid.org/0000-0001-5923-1688

ORCID for Sumeet Mahajan: orcid.org/0000-0001-8923-6666

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