Efficient tailoring of the surface of upconversion nanoparticles via surface-initiated cationic ring-opening polymerization

Decoration of lanthanide-doped upconversion nanoparticles (UCNPs) with polymers to endow the UCNPs with the desired properties for various applications has attracted considerable attention. Herein, we present for the first time that the surface-initiated cationic ring-opening polymerization (CROP) technique can be employed as an effective tool to decorate UCNP with diverse polymers, as exemplified by the successful grafting of hydrophobic poly(epsilon-caprolactone) and hydrophilic hyperbranched polyglycerol from the surface of NaYF4:Yb/Er UCNP. Furthermore, the content of the grafted polymer associated with the thickness of the polymer shell can be controlled by adjusting the feed ratio. Benefiting from the introduction of the polymer shell, the resulting UCNP/polymer nanohybrids simultaneously show strong upconversion luminescence, tunable solution dispersibility, enhanced solution processibility, high biocompatibility, and favorable surface functionality, which make them promising for various applications such as fabrication of light-emitting polymer composites, cellular imaging, and drug delivery. Considering the high robustness and flexibility of the CROP technique, this investigation opens up new avenues for decorating UCNPs with diverse polymers to meet various application requirements.