Making Fluorescent Nylon, Polypropylene, and Polystyrene Microplastics for In Vivo and In Vitro Imaging

Microplastics (MPs) are synthetic environmental pollutants increasingly linked to adverse human health effects. To study their biological impact, researchers require access to environmentally relevant MPs that can be accurately tracked in biological systems. However, most ambient MPs are composed of non-conjugated polymers that lack intrinsic fluorescence, limiting their utility in live-cell or in vivo imaging. Addressing this challenge, we present two alternative labeling approaches that enable visualization, tracking, and quantification of MPs. First, we stained nylon and polypropylene MPs with Rhodamine 6G, a fluorescent dye known for its stability and compatibility with in vivo applications. These labeled MPs retained strong fluorescence in murine lung tissue for up to one week, as confirmed by fluorescent microscopy. Second, we conjugated aminated polystyrene microspheres with IRDye-800CW, a near-infrared fluorophore that enables high-resolution imaging with minimal tissue autofluorescence via an In Vivo Imaging System and confocal microscopy. In vivo experiments revealed organ-specific accumulation of IRDye-labeled MPs, with a 2.8-fold increase in the liver and a 5-fold increase in spleen compared to controls, detectable up to 72 h post-injection. These labeling strategies provide researchers with practical tools to visualize and study the biodistribution of MPs in biological systems, advancing efforts to understand their health implications.