What have we known so far for fluorescence staining and quantification of microplastics: A tutorial review

Abstract

Understanding the fate and toxicity of microplastics (MPs, < 5 mm plastic particles) is limited by quantification methods. This paper summarizes the methods in use and presents new ones. First, sampling and pretreatment processes of MPs, including sample collection, digestion, density separation, and quality control are reviewed. Then the promising and convenient staining procedures and quantification methods for MPs using fluorescence dyes are reviewed. The factors that influence the staining of MPs, including their physicochemical properties, are summarized to provide an optimal operation procedure. In general, the digestion step is crucial to eliminate natural organic matter (NOM) to avoid interference in quantification. Chloroform was reported to be the most appropriate solvent, and 10–20 μg/mL are recommended as optimal dye concentrations. In addition, a heating and cooling procedure is recommended to maintain the fluorescence intensity of MPs for two months. After staining, a fluorescence microscope is usually used to characterize the morphology, mass, or number of MPs, but compositional analysis cannot be determined with it. These fluorescence staining methods have been implemented to study MP abundance, transport, and toxicity and have been combined with other chemical characterization techniques, such as Fourier transform infrared spectroscopy and Raman spectroscopy. More studies are needed to focus on the synthesis of novel dyes to avoid NOM’s interference. They need to be combined with other spectroscopic techniques to characterize plastic composition and to develop image-analysis methods. The stability of stained MPs needs to be improved.

Observing Microplastics in the Environment through Citizen-Science-Inspired Laboratory Investigations

“…Hydrophobic dyes, such as Nile Red (NR), preferentially combine with polymer materials with a lower polarity that are common in microplastics. 93 Prior research has shown that lipophilic dyes are effective in the quantification of small particles because of their high hydrophobicity. 94 NR (C 20 H 18 N 2 O 2 ; MW: 318.37) does not pose health hazards.…”

Development of a machine learning-based method for the analysis of microplastics in environmental samples using µ-Raman spectroscopy

“…The results are given in item concentrations [3]. Often only a few selected particles are analyzed [6,7]. However, this is not sufficient, particularly because -even with accurate sample preparation and mitigation of contamination -there are usually numerous non-plastic particles on a filter.…”

The Raman spectroscopy and SEM/EDS investigation of the primary sources of microplastics from cosmetics available in Poland

“…The most common polyethylene (PE) exhibits four typical bands between 1000 and cm − 1 in Raman spectra (1439 cm − 1 , 1295 cm − 1 , 1129 cm − 1 , cm − 1 ), whereas characteristic FTIR peaks (for instance due to the asymmetric and symmetric stretching of -CH 3 group) can be observed at: ~2915-2918 cm − 1 , ~2845-2850 cm − 1 , ~1463-1469 cm − 1 , ~713-720 cm − 1 . Other used methods include gas chromatography, mass spectrometry, and fluorescent staining (Liu et al, 2022).…”