NIR-II Plastic Particles for Monitoring IntestinalMotility and Microplastic Deposition in Mice

Plastic products are widely used in daily life, leading to the pervasive presence of microplastics, which have posed great threats to human health. However, the relative lack of methods to observe the movement and distribution of microplastics in living animals has retarded the understanding of their biological effects. Fluorescence imaging in the near-infrared II (NIR-II) window with good tissue penetration has greatly expanded its scope for living animals. In this study, we have developed a NIR-II fluorescence imaging platform using polystyrene particles to dynamically visualize microplastic behavior in the gastrointestinal tract of living mice. After oral administration of the fluorescent particles, NIR-II imaging at a frame rate of 30 fps revealed the intestinal motility with a peristaltic frequency of 0.51 ± 0.02 beats per second and food transit velocity of 1.3 ± 0.2 mm/s in healthy mice, which excreted 99% of the fluorescent particles within 24 h. In contrast, constipated and colitis mice displayed impaired intestinal peristalsis and significantly prolonged intestinal retention of microplastics. Moreover, the method disclosed that long-term feeding of microplastics resulted in persistent retention in the intestines and spleen, as confirmed by hyperspectral imaging. The utility of the proposed NIR-II imaging platform for dynamic tracking in mammals provides critical insight into the roles of microplastics in biological systems.