Influence of intrinsic plastics characteristics on Nile Red staining and fluorescence

Nile Red is a lipophilic staining dye often used in the detection of microplastics in environmental samples. This work evaluated the influence of characteristics of plastic particles collected from sandy beaches (n = 60) on fluorescent emissions after Nile Red staining. Most particles presented medium to high fluorescence (81.6%). Polymer type (polyethylene, polypropylene, polystyrene), weathering (i.e., carbonyl index, methyl index), and crystallinity did not affect fluorescence intensity (grey value) or color (RGB values). Conversely, particle color significantly influenced fluorescence, with lower fluorescence seen for some blue, green, and red particles, and higher in some white, yellow, and orange particles, suggesting an influence of pigments used in plastics on Nile Red staining. Wide variations in fluorescence were observed for the same particle color, possibly resulting from the use of different pigments. Therefore, future studies should tackle the issue of the interference of plastic pigments in the detection and characterization of plastic particles.