Luminous Upconverted Nanoparticles as High-Sensitivity Optical Probes for Visualizing Nano- and Microplastics in Caenorhabditis elegans

With the increasing prevalence of plastic pollution, understanding its impact on soil nematodes is crucial for environmental sustainability and food security. Traditional fluorescence-based probes have the limitations of high background noise and interference from autofluorescence. In this study, the luminous upconverted NaYF4:Yb³⁺/Er³⁺ nanoparticles acted as high-sensitivity probes for real-time visualization of ingestion and biodistribution of polystyrene microplastics (PS-MPs) and nanoplastics (PS-NPs) in <i>Caenorhabditis elegans</i>. The novel probes enabled efficient near-infrared-to-visible light conversion. This approach improved the precision of nano- and microplastic detection in biological tissues. Microscopic imaging revealed that the probes effectively distinguished size-dependent plastic distribution patterns, with microplastics remaining in the digestive tract, whereas nanoparticles penetrated intestinal walls and entered systemic circulation. Quantitative fluorescence analysis confirmed that PS-NPs exhibited higher bioavailability and deeper tissue penetration, providing crucial insights into plastic behavior at the organismal level. The different toxicities of PS-NPs and PS-MPs were further confirmed by measurement of the locomotor impairments and the physiological disruptions. These findings emphasize the broader applications of upconverted nanoparticles as advanced bio-imaging probes, offering a sensitive and non-invasive tool for tracking pollutant interactions in environmental and biological systems.