Mesoporous NaGdF₄/Ho–Yb@m-SiO₂ Upconversion Nanophosphors as a Potent Theranostic Probe

Nearly monodispersed NaGdF4/Ho–Yb upconversion nanoparticles (UCNPs) are synthesized by thermolysis of respective rare earth oleates. UCNPs are made biocompatible by mesoporous silica (m-SiO2) coating. These particles exhibit red and green bands in the visible range upon excitation at 980 nm laser. Interestingly, because of the presence of Ho3+ ions, these UCNPs can be excited via UV–vis light in addition to the 980 nm near infrared light. A systematic study is carried out to demonstrate the use of these UCNPs as drug (DOX) carriers. Toxicity studies and bio-imaging using DOX-loaded UCNPs have been demonstrated. UCNPs are also radiolabeled with 177Lu using m-SiO2 coating to demonstrate its potential application as a carrier of the therapeutic radionuclide in vivo for radionuclide therapy. Lu-177 adsorption studies are carried out extensively in order to understand the nature of adsorption, and it is found to be a combination of Langmuir and Freundlich isotherm models. Kinetics of adsorption of Lu3+ ions on the m-SiO2 coating of UCNPs is studied. Overall, the synthesis and physicochemical characterization of NaGdF4/Ho–Yb@m-SiO2 upconversion nanocrystals and their potential utilities in multimodal biomedical applications are amply demonstrated.