Polymer-Coated Ultrastable and Biofunctionalizable Lanthanide Nanoparticles.

Lanthanide-containing nanoparticles (LnNPs), for example, NaYF4, are considered to be one of the most promising platforms for biological and material applications due to their unique and unusual magnetic and upconversion fluorescent properties. However, limited water dispersity, low long-term colloidal stability, and difficulty in further functionalization greatly narrow the scope of their application in the real world. Herein, we report a facile strategy to counter the aforementioned barriers to the expanding use of LnNPs that involves surface-coating the LnNPs with poly(ethylene glycol)-b-poly(pentafluorophenyl methacrylate)/phosphonic acid and subsequently shell cross-linking with NH2-PEG-NH2. The cross-linked PEG layer provided good water dispersity, nonfouling characteristics, and excellent long-term colloidal stability in phosphate-buffered saline in the range of 25-60 °C, whereas the high reactivity of the pentafluorophenyl ester with the amino group brought about ease of incorporation of functional moieties into LnNPs. Particularly, it was found for the first time that LnNPs with surface coating could endure the freeze-drying process without any sign of aggregation, which would not only greatly decrease the weight and storage and shipping room but also increase the storage shelf life with the preservation of their inherent properties, especially for LnNPs with some fragile bioconjugates while in solution.