Innovative portable microplastic detector using a continuous flow technique with fluorescence Nile red–graphene oxide

This research is the first report on the development of an innovative microplastic detection method that combines a continuous flow system for sample processing with fluorescent staining for microplastic visualization and a portable fluorescence sensor for rapid analysis. This flow system could be loaded with large sample volumes of 1–5 L at 15 mL min−1 flow rate. Microplastics were captured by a 300 µm stainless steel sieve within the chamber and then stained with a 1:1 mixture of Nile red (NR) and graphene oxide (GO) fluorescent dye. The staining process involved a 15-min dyeing step, followed by a 15-min drying step. Microplastics were then detected using a portable fluorescence sensor. Results indicated that the NR–GO composite dye exhibited a considerably enhanced fluorescence intensity, with a fourfold increase over the dye without GO. Under UV illumination, stained microplastic samples exhibited yellow, red, and orange colors. The observed color depends on the functional groups present in the microplastic polymers. Under optimal conditions, a linear calibration of polyethylene was established in the range of 0.1–1.2 mg with a high correlation coefficient (R2) of 0.99. This work successfully applied the proposed semi-automated system for the quantitative analysis and classification of microplastics in real samples.