4:45 PM - 5:00 PM
[MIS20-12] Non-contact real-time identification of microplastics in flow by combining holography and Raman spectroscopy
Keywords:Microplastics, Monitoring , Holography, Raman spectroscopy
Hundreds of millions of tons of plastic waste are generated, and millions of tons enter the ocean every year [1]. “Microplastics”, with the size of less than 5 mm, become coated with biofilms, get attached to other particles, or ingested by microorganisms while floating in the ocean, and transported to all parts of the oceans. The global awareness of pollution in marine and other aquatic environments by microplastics has risen recently [2]. While spectroscopic techniques such as Fourier transformed infrared and Raman spectroscopy have been widely used for identification of plastics collected from aquatic environments, these are time-consuming due to the need for separation from other organic and inorganic particles, filtration, and long measurement time [3]. In this work, a novel method for non-contact fast identification of microplastics suspended in water was investigated.
An integrated method of holography and Raman spectroscopy for in situ real-time monitoring of microplastics is reported. Polystyrene (PS) and poly(methyl methacrylate) (PMMA) pellets with a size of 3 mm located in a 20 cm water channel were illuminated using a collimated continuous wave laser beam with a diameter of 4 mm and wavelength of 785 nm. The same laser beam was used to take a holograms for size and shape information, and produce a Raman spectrum for composition information of the suspended material. By the proposed method, PS and PMMA beads in a large water volume were successfully identified using a compact setup [4]. We have also demonstrated classification of particle types by this combined morphological and chemical analysis. While particles with distinctive shapes, such as plankton, can be easily identified by holography, chemical analysis by Raman measurements is necessary for some particles as shown in the Figure. Corresponding Raman peaks of the materials are observed in the Raman spectra of plastic pellets of PS and PMMA. Inorganic matter (Foraminifera) shows a CaCO3 peak and other peaks that match Raman peaks taken for the same sample in air as a ground truth. While no obvious Raman peak is observed in the spectrum of organic matter (paste of replicated marine snow), a broad fluorescence peak is seen.
The proposed method demonstrates the potential for non-contact continuous in situ monitoring of marine particles, including microplastics, suspended in water without the need for collection/extraction. It is particularly promising for long-term measurements in deep-water columns, where the particle density is extremely low. The concept of the measurement process using the system is the following: holographic images are continuously captured in an open measurement chamber with a high frame rate to detect a particle. When a particle is detected, the chamber is closed to trap the particle and a Raman measurement is initiated (which takes several tens of seconds, but can be faster using higher power lasers). After the Raman measurement, the chamber is opened again and onset of holographic imaging waits for the next particle. The whole measurement process can be fully automated, which makes it possible to deploy the system on an autonomous platform such as autonomous underwater vehicles and buoys. This could be game-changing for current sampling-based analysis and will contribute to the understanding of global-scale microplastic pollution in aquatic environments.
References:
[1] J. Jambeck, R. Geyer, C. Wilcox, et al., Science (2015); 347, 768–771.
[2]T. Galloway, C. Lewis, Curr. Biol. (2017); 27, R445-R446.
[3] W. J. Shim, S. H. Hong, S. E. Eo, Anal. Methods (2017); 9, 1384-1391.
[4] T. Takahashi, Z. Liu, T. Thevar, et al., Appl. Optics (2020); 59, 5073-5078.
An integrated method of holography and Raman spectroscopy for in situ real-time monitoring of microplastics is reported. Polystyrene (PS) and poly(methyl methacrylate) (PMMA) pellets with a size of 3 mm located in a 20 cm water channel were illuminated using a collimated continuous wave laser beam with a diameter of 4 mm and wavelength of 785 nm. The same laser beam was used to take a holograms for size and shape information, and produce a Raman spectrum for composition information of the suspended material. By the proposed method, PS and PMMA beads in a large water volume were successfully identified using a compact setup [4]. We have also demonstrated classification of particle types by this combined morphological and chemical analysis. While particles with distinctive shapes, such as plankton, can be easily identified by holography, chemical analysis by Raman measurements is necessary for some particles as shown in the Figure. Corresponding Raman peaks of the materials are observed in the Raman spectra of plastic pellets of PS and PMMA. Inorganic matter (Foraminifera) shows a CaCO3 peak and other peaks that match Raman peaks taken for the same sample in air as a ground truth. While no obvious Raman peak is observed in the spectrum of organic matter (paste of replicated marine snow), a broad fluorescence peak is seen.
The proposed method demonstrates the potential for non-contact continuous in situ monitoring of marine particles, including microplastics, suspended in water without the need for collection/extraction. It is particularly promising for long-term measurements in deep-water columns, where the particle density is extremely low. The concept of the measurement process using the system is the following: holographic images are continuously captured in an open measurement chamber with a high frame rate to detect a particle. When a particle is detected, the chamber is closed to trap the particle and a Raman measurement is initiated (which takes several tens of seconds, but can be faster using higher power lasers). After the Raman measurement, the chamber is opened again and onset of holographic imaging waits for the next particle. The whole measurement process can be fully automated, which makes it possible to deploy the system on an autonomous platform such as autonomous underwater vehicles and buoys. This could be game-changing for current sampling-based analysis and will contribute to the understanding of global-scale microplastic pollution in aquatic environments.
References:
[1] J. Jambeck, R. Geyer, C. Wilcox, et al., Science (2015); 347, 768–771.
[2]T. Galloway, C. Lewis, Curr. Biol. (2017); 27, R445-R446.
[3] W. J. Shim, S. H. Hong, S. E. Eo, Anal. Methods (2017); 9, 1384-1391.
[4] T. Takahashi, Z. Liu, T. Thevar, et al., Appl. Optics (2020); 59, 5073-5078.