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Updated: Aug 22, 2025
Protocol for Microplastics Sampling on the Sea Surface and Sample Analysis
Published on: December 16, 2016
Labeling Microplastics with Fluorescent Dyes for Detection, Recovery, and Degradation Experiments
Zhiqiang Gao1, Kendall Wontor1, James V Cizdziel1
1Department of Chemistry and Biochemistry, University of Mississippi, University, MS 38677, USA.
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.
Insights
Researchers developed a simple method to create fluorescent microplastics (MPs) for environmental analysis. This standardized staining technique enhances MP detection in various water and sludge samples, improving research accuracy.
Area of Science:
- Environmental Science
- Analytical Chemistry
- Polymer Science
Background:
- Fluorescence detection is crucial for microplastic (MP) analysis.
- Current staining methods lack standardization in dye concentration, solvents, incubation, and temperature.
- Limited availability of diverse fluorescent MPs hinders research.
Purpose of the Study:
- To develop a simple, optimized, and standardized method for creating fluorescent microplastics (MPs).
- To evaluate the effectiveness of textile dyes and Nile red for staining various polymer types and morphologies.
- To assess the impact of staining on MP characteristics and their detectability in environmental matrices.
Main Methods:
- Stained 17 different virgin and weathered polymer types (fragments, fibers, foams, pellets, beads) using 4 textile dyes and Nile red.
- Optimized staining conditions including dye concentration, temperature, and incubation time in aqueous solutions.
- Analyzed MP characteristics (surface, mass, chemical) using FTIR and stereomicroscopy.
- Tested stained MP detectability in freshwater, saltwater, sediment slurry, and wastewater sludge.
Main Results:
- Optimal aqueous staining conditions identified: 70°C for 3 hours.
- Recommended dye concentrations: 5 mg/mL (iDye), 55 mg/mL (Rit dyes), and 2 µg/mL (Nile red).
- Red fluorescent signals showed stronger intensity than green.
- Staining did not significantly alter MP surface, mass, or chemical properties.
- Stained MPs remained strongly fluorescent in environmental samples for several days.
Conclusions:
- A straightforward and simple protocol for producing customized fluorescent MPs was established.
- The method enhances the quantification of MPs in laboratory-controlled experiments.
- This standardized approach improves microplastic detection and analysis in environmental research.
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