Nile red staining in microplastic analysis—proposal for a reliable and fast identification approach for large microplastics

A variety of methods concerning the identification of microplastics in environmental samples exist. While visual identification is often used, implemented easily, and cost-efficient but implying biased results, spectroscopic or chromatographic approaches are reliable but time-consuming and need specific equipment. Nile red staining is an available alternative and complement method for identifying microplastics. In this study, Nile red staining and subsequent photographing in a UV light photobox was tested on its reliability and feasibility. The approach was compared with a second identification process using again staining but a fluorescence microscope. Selected identified microplastic particles were analyzed by μ-Raman spectroscopy to prove their polymeric origin. The results show that the presented approach is faster compared with the use of a fluorescence microscope or μ-Raman spectroscopy. Furthermore, it is cost-effective as well as accurate for large microplastics > 0.63 mm and, therefore, may be applied when large sample volumes need to be analyzed. Graphical abstract.