Labeling Microplastics with Fluorescent Dyes for Detection, Recovery, and Degradation Experiments

Abstract

Staining microplastics (MPs) for fluorescence detection has been widely applied in MP analyses. However, there is a lack of standardized staining procedures and conditions, with different researchers using different dye concentrations, solvents, incubation times, and staining temperatures. Moreover, with the limited types and morphologies of commercially available MPs, a simple and optimized approach to making fluorescent MPs is needed. In this study, 4 different textile dyes, along with Nile red dye for comparison, are used to stain 17 different polymers under various conditions to optimize the staining procedure. The MPs included both virgin and naturally weathered polymers with different sizes and shapes (e.g., fragments, fibers, foams, pellets, beads). We show that the strongest fluorescence intensity occurred with aqueous staining at 70 °C for 3 h with a dye concentration of 5 mg/mL, 55 mg/mL, and 2 µg/mL for iDye dyes, Rit dyes, and Nile red, respectively. Red fluorescent signals are stronger and thus preferred over green ones. The staining procedure did not significantly alter the surface, mass, and chemical characteristics of the particles, based on FTIR and stereomicroscopy. Stained MPs were spiked into freshwater, saltwater, a sediment slurry, and wastewater-activated sludge; even after several days, the recovered particles are still strongly fluoresced. The approach described herein for producing customized fluorescent MPs and quantifying MPs in laboratory-controlled experiments is both straightforward and simple.

A Critical Review on Current Challenges in the Analysis of Microplastics in Food Samples

“…72 The dyeing method is typically used to facilitate frequent identification of MPs. Based on previous reports, Rose Bengal, 73 Nile red, 74 Eosin B, 75 and Oil Red EGN 76 were used as dyes in this method (Figure 4). Among these, Nile red dye provided the best results.…”

Fast Forward: Optimized Sample Preparation and Fluorescent Staining for Microplastic Detection

“…Nevertheless, some polymer types can be sensitive to high temperatures [29][30][31]. Other studies have also revealed that higher temperatures have a positive impact on the staining procedure [25][26][27][28]. Higher temperatures can yield a better adsorption of the fluorescent dye onto the MP surface and into the polymeric network.…”

Microplastic in situ detection based on a portable triboelectric microfluidic sensor

“…7,8 Fluorescence microscopy (FM) combines the magnication capabilities of an optical microscope with the uorescence emission properties of dyed compounds to generate a magni-ed, uorescent image. 9 FM provides information on size, shape, and morphology, and it can also be used to count and determine the concentration of MPs. Also, scanning electron microscopy (SEM) uses an electron beam instead of visible light to scan the surface of an object to create a high-resolution, magnied image, but it is costly and requires much training to use.…”