A rapid-screening approach to detect and quantify microplastics based on fluorescent tagging with Nile Red

Abstract

A new approach is presented for analysis of microplastics in environmental samples, based on selective fluorescent staining using Nile Red (NR), followed by density-based extraction and filtration. The dye adsorbs onto plastic surfaces and renders them fluorescent when irradiated with blue light. Fluorescence emission is detected using simple photography through an orange filter. Image-analysis allows fluorescent particles to be identified and counted. Magnified images can be recorded and tiled to cover the whole filter area, allowing particles down to a few micrometres to be detected. The solvatochromic nature of Nile Red also offers the possibility of plastic categorisation based on surface polarity characteristics of identified particles. This article details the development of this staining method and its initial cross-validation by comparison with infrared (IR) microscopy. Microplastics of different sizes could be detected and counted in marine sediment samples. The fluorescence staining identified the same particles as those found by scanning a filter area with IR-microscopy.

Food web transfer of plastics to an apex riverine predator

“…This reflects the size range of material we know to be present in dipper prey, while also offering a clearly defined and repeatable method for comparison by others (Windsor, Tilley, et al, 2019). Although methods are available that could potentially resolve and identify microplastics down to approximately 10 µm in digested organic samples, for example through scanning using fluorescent staining (Maes, Jessop, Wellner, Haupt, & Mayes, 2017) and focal plane array FT‐IR (Primpke, Lorenz, Rascher‐Friesenhausen, & Gerdts, 2017), these methods have not yet been applied routinely to the quantitative detection of microplastic particles in faecal matter.…”

Effects of environmentally relevant concentrations of microplastic fibers on Pacific mole crab (Emerita analoga) mortality and reproduction

“…Nile Red, a lipid-soluble fluorescent dye that stains hydrophobic materials, can improve the accuracy of microplastic quantification (Shim et al 2016;Maes et al 2017). PP, PE, PS, the most commonly identified microplastics on beaches and in surface water (Hidalgo-Ruz et al 2012), are effectively stained with Nile Red (Shim et al 2016).…”

Micro-and macro-plastics in marine species from Nordic waters

“…, Wesch et al (2016) and Löder and Gerdts (2015). There has also been suggested low-cost techniques that involves the use of polarized light microscopes to observe birefringent properties of polymers, or the use of Nile Red to colour plastic polymers (Maes et al, 2017;Shim et al, 2017). These lowcost techniques might have a potential to solve problems that exist with more traditional techniques; such as expensive and sensitive laboratory equipment, mismatches/errors with visual identification (which also requires extensive use of manpower), and due to chemical identification of polymers due to problems with weathered, bio-fouled and natural polymers.…”

“…The visual identification is subjective and skill dependent, and only this method is used there may be over or underestimations. Staining methods like Nile Red Dye might reduce these difficulties (Maes et al, 2017), but also the more classical methods like FTIR and Raman spectroscopy.…”