Upconversion Colloid for Tracking Cellular Uptake of Nanoparticles.

Upconverting nanoparticles, which transform low-energy infrared radiation into high-energy visible or UV light, show great potential in today's technology. High-quality upconversion colloid (UCC) consisting of lanthanide-based nanoparticles with a diameter of ~10 nm was obtained using a combination of two processes: high-temperature coprecipitation and hydrothermal treatment in an autoclave. The UCC was then PEGylated with PEG-alendronate (PEG-Ale) to facilitate its dispersion in aqueous cell culture media intended for in vitro cell uptake assays. The surface modification of the nanoparticles increased both the colloidal stability in water and the upconversion emission by mitigating surface quenching. UCC@Ale-PEG was characterized by transmission and scanning electron microscopy, dynamic light scattering, and fluorescence microscopy detecting upconversion photoluminescence emission. The results of an in vitro assay revealed that this new generation of UCC can be internalized by various cell types, including epithelial cells and macrophages, upon several hours of exposure, suggesting broad application potential of this type of UCC in biomedicine, bioengineering, and environmental sciences.