The Dye-Sensitization Of Upconversion Nanoparticles

Upconversion nanoparticles can convert infrared light into visible light through sequential absorption of multiple photons. Thus, upconversion nanoparticles have broad applications in many fields such as solid-state lasers, solar cells and laser security etc. In recent years, researchers pay more attentions on its potential applications in theranostics. Compared with traditional biomarkers, the excitation wavelength of upconversion nanoparticles was located at infrared light, which can minimize the photo damage of biological organizations.At the same time, the excitation of infrared light can increase the detective depth and decrease auto-fluorescence of tissue, which could lead a high signal-to-noise ratio. Besides, upconversion nanoparticles also have a lot of advantages such as low toxicity, non-photobleaching, high fluorescence stability and well biocompatibility. These unique specialty make upconversion nanoparticles have large potential in bioimaging, photothermal therapy, photodynamic therapy and drug delivery. But there are also some challenges in biological applications of upconversion nanoparticles. Firstly, the excitation wavelength of common upconversion nanoparticles was located at 980nm, which is corresponding to the absorption peak of water. This could lead thermal damage of tissue when it is exposed to laser-excitation long time. Secondly, upconversion nanoparticles have low fluorescence efficiency due to its weak absorption of lanthanide ions. The paper aimed at solving these two drawbacks above and the major achievements are as belows:We introduced a new lanthanide ions Nd3+ into the upconversion nanoparticles and successfully synthesized NaYFv.Yb/Er/Nd. Through the cascade energy transfer of Nd3+→Yb3+→Er3+, the excitation wavelength of upconversion nanoparticles was tuned to 800 nm successfully. We also designed a new type of core-sell structure NaYF4:Yb/Er@NaYF4.Yb/Nd and improve the luminance intensity of upconversion nanoparticles.We synthesized dyes of IR-806, and used it to sensitize upconversion nanoparticles. This dye has a large absorption cross section and could transfer the energy to upconversion nanoparticles. After sensitization, the fluorescence intensity of upconversion nanoparticles was improved largely.We also made a research on the temperature sensing of Nd3+ doped upconversion nanoparticles and photothermal conversion of dye-upconversion nanoparticles composite nanostructure. The dye-upconversion nanoparticles composite nanostructure has a good performance of photothermal conversion and it has the prospect to realize multifunction integration of optical imaging and photothermal therapy.