Nile Red staining for the detection of microplastics: a comprehensive study on the emission spectra

Abstract Several research groups have explored Nile Red staining of artificial and natural environmental samples to provide an inexpensive and relatively fast analysis tool for identifying microplastics. Yet, most of these studies were based on a limited set of polymer samples, and primarily base polymers were investigated, i.e., uncolored and non-weathered polymers. Hence, the influence of pigments, weathering or erosion on the luminescence of stained microplastics is not yet well understood. To fill this gap, we performed photoluminescence (PL) spectroscopy and photoluminescence excitation spectroscopy on a variety of Nile Red-stained plastics and non-plastic samples. The investigated sample set includes commercially available plastic samples to investigate how additives and pigments in the polymer material impact the PL spectra via their auto-fluorescence. Besides, we study the influence of surface roughness on the emitted PL. Finally, we examined 20 microparticles collected from the Lahn River using PL spectroscopy to cross-validate our observations.