Fabrication and evaluation of chitosan/NaYF4:Yb3 +/Tm3 + upconversion nanoparticles composite beads based on the gelling of Pickering emulsion droplets

- NaYF4:Yb3 +/Tm3 + UCNPs were coated by F127 to improve aqueous dispersibility.
- NaYF4:Yb3 +/Tm3 + UCNPs were assembled with chitosan to fabricate the composite beads (CMs).
- Pickering emulsions stabilized by UCNPs exhibited uniform and satisfactory emulsion droplets.
- The CMs prepared by the gelling of emulsion droplet preserved upconversion luminescent property.
- The resultant CMs showed good drug-loading capacity, release performance and biocompatibility.

The rare earth ion doped upconversion nanoparticles (UCNPs) synthesized by hydrophobic organic ligands possess poor solubility and low fluorescence quantum yield in aqueous media. To conquer this issue, NaYF4:Yb3 +/Tm3 + UCNPs, synthesized by a hydrothermal method, were coated with F127 and then assembled with chitosan to fabricate the chitosan/NaYF4:Yb3 +/Tm3 + composite beads (CS/NaYF4:Yb3 +/Tm3 + CBs) by Pickering emulsion system. The characterization results revealed that the as-synthesized NaYF4:Yb3 +/Tm3 + UCNPs with an average size of 20 nm exhibited spherical morphology, high crystallinity and characteristic emission upconversion fluorescence with an overall blue color output. The NaYF4:Yb3 +/Tm3 + UCNPs were successfully conjugated on the surface of chitosan beads by the gelling of emulsion droplets. The resultant CS/NaYF4:Yb3 +/Tm3 + CBs showed good upconversion luminescent property, drug-loading capacity, release performance and excellent biocompatibility, exhibiting great potentials in targeted drug delivery and tissue engineering with potential tracking capability and lasting release performance.

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