In this study, spherical or hexagonal NaYF₄:Yb,Er nanoparticles (UCNPs) with sizes of 25 nm (S-UCNPs) and 120 nm (L-UCNPs) were synthesized by high-temperature coprecipitation and subsequently modified with three kinds of polymers. These included poly(ethylene glycol) (PEG) and poly(N,N-dimethylacrylamide-co-2-aminoethylacrylamide) [P(DMA-AEA)] terminated with an alendronate anchoring group, and poly(methyl vinyl ether-co-maleic acid) (PMVEMA). The internalization of nanoparticles by rat mesenchymal stem cells (rMSCs) and C6 cancer cells (rat glial tumor cell line) was visualized by electron microscopy and the cytotoxicity of the UCNPs and their leaches was measured by the real-time proliferation assay. The comet assay was used to determine the oxidative damage of the UCNPs. An in vivo study on mice determined the elimination route and potential accumulation of UCNPs in the body. The results showed that the L- and S-UCNPs were internalized into cells in the lumen of endosomes. The proliferation assay revealed that the L-UCNPs were less toxic than S-UCNPs. The viability of rMSCs incubated with particles decreased in the order S-UCNP@Ale-(PDMA-AEA) > S-UCNP@Ale-PEG > S-UCNPs > S-UCNP@PMVEMA. Similar results were obtained in C6 cells. The oxidative damage measured by the comet assay showed that neat L-UCNPs caused more oxidative damage to rMSCs than all coated UCNPs while no difference was observed in C6 cells. An in vivo study indicated that L-UCNPs were eliminated from the body via the hepatobiliary route; L-UCNP@Ale-PEG particles were almost eliminated from the liver 96 h after intravenous application. Pilot fluorescence imaging confirmed the limited in vivo detection capabilities of the nanoparticles.

In this report, we synthesized hexagonal NaYF₄:Yb,Er upconverting nanoparticles (UCNPs) of 171 nm in size with a narrow particle size distribution. To address their colloidal stabi-lity in aqueous media and to incorporate a photosensitizer that can produce reactive singlet oxygen (¹O₂) to kill tumor cells, UCNPs were conjugated with 6-bromohexanoic acid-functionalized Rose Bengal (RB) and coated with PEG-alendronate (PEG-Ale). The particles were thoroughly characterized by transmission electron microscopy, dynamic light scattering, ATR FTIR, X-ray photoelectron spectroscopy, thermogravimetric analysis, and spectrofluorometry, and ¹O₂ formation was detected using a 9,10-diphenylanthracene spectrophotometric probe. Cytotoxicity determination on rat mesenchymal stem cells by using the MTT assay showed that neutralization of the large positive surface charge of neat UCNPs with PEG-Ale and the bound RB sensitizer significantly reduced the concentration-dependent cytotoxicity. The presented strategy shows great potential for the use of these particles as a novel agent for the photodynamic therapy of tumors.

Photodynamic therapy (PDT) is a highly selective, clinically approved, minimally invasive technique that effectively eliminates cancer cells. Its effectiveness is limited by poor light penetration into tissue and the hydrophobic nature of photosensitizers, highlighting the need for new approaches to treatment. Here, a theranostic upconversion nanoplatform, consisting of a NaYF₄:Yb,Er,Tm,Fe core and a NaHoF₄ shell codoped with Yb, Nd, Gd and Tb ions, was designed to enhance PDT outcomes by integrating multi-wavelength upconversion luminescence, T₂-weighted magnetic resonance imaging (MRI) and PDT. The synthesized core–shell upconversion nanoparticles (CS-UCNPs) were coated with new verteporfin (VP)-conjugated alendronate-terminated poly(N,N-dimethylacrylamide-co-2-aminoethyl acrylate) [Ale-P(DMA-AEA)] grafted with poly(ethylene glycol) (PEG). Under 980 nm NIR irradiation, CS-UCNP@Ale-P(DMA-AEA)-PEG-VP nanoparticles generated reactive oxygen species (ROS) due to the efficient energy transfer between CS-UCNPs and VP. In a pilot preclinical study, intratumoral administration of nanoparticle conjugates to mice, followed by exposure to NIR light, induced necrosis of pancreatic tumor and suppressed its growth.

Spherical or hexagonal NaYF4:Yb,Er nanoparticles (UCNPs) with sizes of 25 nm (S-UCNPs) and 120 nm (L-UCNPs) were synthesized by high-temperature coprecipitation and subsequently modified with three kinds of polymers. These included poly(ethylene glycol) (PEG) and poly(N,N-dimethylacrylamide-co-2-aminoethylacrylamide) [P(DMA-AEA)] terminated with an alendronate anchoring group, and poly(methyl vinyl ether-co-maleic acid) (PMVEMA). The internalization of nanoparticles by rat mesenchymal stem cells (rMSCs) and C6 cancer cells was visualized by electron microscopy and the cytotoxicity of the UCNPs and their leaches was measured by the real time proliferation assay. Comet assay was used to determine oxidative damage of UCNPs. In vivo study on mice determined the elimination route and potential accumulation of UCNPs in the body. The results showed that the L- and S-UCNPs were internalized into cells in the lumen of endosomes. Proliferation assay revealed that L-UCNPs were less toxic than S-UCNPs. The viability of rat mesenchymal stem cells (rMSCs) incubated with particles decreased in the order S-UCNP@Ale-(PDMA-AEA) > S-UCNP@Ale-PEG > S-UCNPs > S-UCNP@PMVEMA. Similar results were obtained in C6 cells. Oxidative damage measured by the Comet assay showed that neat L-UCNPs caused oxidative damage to rMSCs more than all coated UCNPs while no difference was observed in C6 cells. An in vivo study indicated that L-UCNPs were eliminated from the body via the hepatobiliary route; L-UCNP@Ale-PEG particles were almost eliminated from the liver 96 h after intravenous application. Pilot fluorescence imaging confirmed the limited in vivo detection capabilities of the nanoparticles.