13 January 2021
Dark-field hyperspectral microscopy for identification of microplastics and nanoplastics in living organisms

A paper by Kazan Federal University has recently been published in Environmental Pollution.

Artificial polymer materials are omnipresent today. They are employed in fabrication of various appliances, household items, clothes, and they are added to cosmetics. Unfortunately, synthetic plastic materials are practically not biodegradable, the recycling rate is low, and as a result, the tonnage of polymer waste is constantly growing, polluting the environment. According to the World Wildlife Fund, about 12 million tons of plastic ends up in the oceans every year.

The co-author of this study, Chief Research Associate (Bionanotechnology Lab) Rawil Fakhrullin explains, “Under the influence of external factors in nature, there is a gradual degradation of bulk plastic to microplastics (particle size less than 5 mm) and nanoplastics (particle size less than 1 micron). As a result, microscopic particles enter the human organism via the food chain, as well as through other pathways, which can initiate a number of pathologies. Determining the level of micro- and nanoplastics contamination in biological objects, assessing food safety and studying the mechanisms of ingestion of microplastics by living organisms are important interdisciplinary challenges. To address these challenges, we need effective methods for the detection, identification and localization of microplastics in biological objects.”

The technique is based on dark-field hyperspectral microscopy. As Dr Fakhrullin says, “Dark-field microscopy is a special way of illuminating samples where a direct light beam is cut off by a stopper, while side beams pass through the sample and form an image appearing as bright spots on the dark background - hence the name. This contrasting technique allows for visualizing particles having sizes much below the resolution limit of a conventional bright-field  optical microscope. In addition, a microscope-attached spectrometer is used to collect spectral data for the chemical identification of particles.”

The researchers managed to visualize polymer nano- and microparticles (polystyrene, polymethylmethacrylate and melamine-formaldehyde resin) using a dark-field microscope' the spectral identification was applied to  identify the particles of various chemical compositions based on characteristic spectral curves.

In this study, dark-field hyperspectral microscopy was reported for the first time for visual detection and quantitative analysis of microplastics in living organisms. Free-living soil nematodes Caenorhabditis elegans were used as a model organism. The detection limit was down to 2-3 plastic particles per organism, and the minimal detection size for polystyrene particles was 100 nm, which is much lower than the previously reported methods (ca. 80 micrometers).

This technique is useful for rapid examination of relatively large specimens, such as microscopic invertebrates (protozoa, worms, crustaceans, mollusks, etc.), as well as small vertebrates (fish larvae), where the distribution of a very limited number of isolated particles can be detected within a few minutes. This non-destructive method will be utilized to detect and estimate the amount of polymer particles in the environment, as well as to study their distribution in tissues and organs.

Dark-field hyperspectral microscopy for label-free microplastics and nanoplastics detection and identification in vivo: A Caenorhabditis elegans study


Source text: Larisa Busil

Translation: Yury Nurmeev, Rawil Fakhrullin

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