Internal Loading of Environmentally Friendly InP/ZnSe/ZnS QDs in Bovine Milk Exosomes

To enable stable and reliable fluorescence tracking in biological environments, this study presents a highly efficient, cadmium-free, and eco-friendly platform for exosome labeling using InP/ZnSe/ZnS quantum dots (QDs). QDs, known for high efficiency, were synthesized using a hot-injection method. To ensure water dispersibility and biocompatibility, the QD oleic acid (OA) surface ligands were sequentially exchanged with 11-mercaptoundecanoic acid (MUA) and polyethylene glycol (PEG) to internalize of QDs within exosomes. Structural unchangeable bovine milk-derived exosomes were purified for exosome internalization using electrophoretic oscillation-assisted tangent flow filtration (EPOTF) with 200 nm SiN _x nanofilters. Ultrasonic treatment was optimized to internalize QDs into exosomes without causing structural deformation, which was confirmed by TEM imaging. The resulting QD-exosomes retained 89% of their initial photoluminescent intensity under continuous laser exposure, in contrast to a significant drop to 10% for conventional PKH67-labeled exosomes. Confocal microscopy demonstrated efficient uptake of QD-exosomes into HaCaT cells and distinct localization around the nucleus. This approach, which integrates eco-friendly QD synthesis, exosome-compatible surface modification, structurally unchangeable ultrasonic embedding, and dual-stage purification, provides a robust and scalable strategy for bioimaging and is suitable for real-time imaging, targeted drug delivery, and advanced nanomedicine applications.