Exploring Nile Red staining as an analytical tool for surface-oxidized microplastics

Microplastics (MPs), defined as plastic particles smaller than 5 mm, have garnered considerable attention owing to their potential biological impact on human health. These particles exhibit a range of physicochemical properties, including size, shape, and surface oxidation. Nile Red is a prominent tool for detecting microplastics, enabling staining for dynamic analyses within biological systems. However, the efficacy of Nile Red staining for surface-oxidized MPs remains unclear. Therefore, we applied Nile Red dye to stain surface-oxidized polyethylene and polyvinyl chloride and observed that both materials were effectively stained, although the fluorescence intensity varied according to different hydrophobic dynamics. Imaging analysis revealed a correlation between the fluorescence intensity score and the degree of surface oxidation, as determined using the carbonyl index calculated from attenuated total reflection-Fourier transform infrared spectroscopy data. Collectively, these findings offer novel analytical approaches for investigating environmental MPs, enhancing our understanding of their behavior and impact.