Development of a platform for quantum-dot-labeled polyethylene nanoplastics for dynamic analytical applications

Microplastics (MPs) are defined as plastic particles smaller than 5 mm, while nanoplastics (NPs) are particles with a diameter less than 1 µm. Both are abundant in the environment and human exposure to them is inevitable. To fully understand the risks posed by plastics to humans, understanding their hazards and kinetics in the body is crucial. However, currently available particles for kinetic analysis, especially for NPs, are limited to spherical polystyrene polymers. This study assessed polyethylene (PE) and prepared PE NPs (nPE) fluorescently labeled with quantum dots (Qdots). Fluorescently labeled nPE was prepared by dissolving and reprecipitating PE MPs (mPE) using Qdots, very small fluorescent particles containing zinc and indium. Microscopic observation and particle size distribution measurements showed that spherical particles smaller than 1 µm were prepared. ATR-IR analysis showed that the fluorescently labeled nPE did not alter surface properties. Fluorescence intensity measurements showed that the fluorescence was sufficiently high for analysis. Evaluation of the fluorescence stability of green and red fluorescent nPE showed that the fluorescence did not fade after one-week suspension in ethanol. Additionally, ICP-MS analysis revealed that Qdots were incorporated into the particles. Cellular uptake assays demonstrated that surface-oxidized labeled nPE exhibited a greater tendency for adhesion to and internalization by a monocyte-derived macrophage-like cell line. This method is versatile and can be adapted to label other polymer types. Collectively, the labeling method established in this study is expected to be useful for analyzing the intracellular and in vivo kinetics of NPs in the environment.