A dye is a colored substance that has an affinity for the substrate applied to it.

Based on selective fluorescent staining with Nile red (NR), and then density extraction and filtration, a new method for the analysis of microplastics in environmental samples was proposed. Dyes stick to plastic surfaces and fluoresce when irradiated with blue light. Fluorescence emission was detected by simple photographic examination of an orange filter. Image analysis allows the identification and counting of fluorescent particles. The enlarged image can be recorded and tiled to cover the entire filter area, thus detecting particles of a few microns. The discoloration properties of Nile red also provide the possibility of plastic classification based on the surface polar characteristics of the recognized particles. Anthocyanin dye can be used to quantify the amount of dsDNA in the sample. The linearity of fluorescence was obtained by measuring the fluorescence intensity at the optimal excitation and emission maxima as a function of the DNA amount of the six dyes.