Application of Eco-Friendly Fluorescent Dyes in Microplastic Detection

Abstract The detection of microplastics using fluorescent staining has gained increasing attention due to the need for efficient and cost-effective analytical approaches. This study evaluates the effectiveness of three eco-friendly fluorescent dyes─coumarin-6, coumarin-153, and curcumin─while Nile Red was used as a control, for staining pristine and mechanically and thermally damaged polymer standards under ultraviolet (UV), blue, and green light illumination. Several commonly occurring polymers were analyzed to assess staining efficiency and intensity distribution. The results showed that polypropylene (PP) was the most difficult polymer to stain, with effective fluorescence achieved only using Nile Red and all tested concentrations of coumarin-6. In contrast, polyethylene terephthalate (PET) exhibited the highest staining efficiency, fluorescing under both UV and blue light with all dyes except coumarin-153 at lower concentrations. Optimal staining of high-density polyethylene (HDPE) was achieved using 50 μg mL–1 coumarin-6 under UV illumination, while Nile Red exhibited the highest fluorescence intensity under blue light, regardless of polymer damage. Mechanical and thermal damage generally increased fluorescence intensity and improved uniformity of staining across polymers. However, this trend was not observed for PP, where damage resulted in increased fluorescence asymmetry. Overall, the findings demonstrate that polymer type, dyes, illumination source, and material damage level strongly influence microplastic staining efficiency and should be carefully considered in microplastic analysis.