Upconversion Nanoparticles Coated with Mesoporous Silica Nanoshells Loaded with Dyes for Fine-Tuned Multicolor Emission in Bioimaging Applications

Multicolor-emitting nanoparticles have drawn great attention in various applications such as biosensors, bioimaging labels, and displays. Upconversion nanoparticles are a great candidate for multicolor emitters because of their high photostability, multiple emission bands in visible ranges, and large anti-Stokes shift for a high signal-to-noise ratio. There have been many efforts to fine-tune the emission color of upconversion nanoparticles by exploiting complex energy transfer pathways at the expense of upconversion efficiency. Here, we report a facile strategy to fine-tune the emission color of β-NaYF4:20% Yb3+, 2% Er3+ upconversion nanoparticles by adopting a mesoporous silica nanoshell with controllable porosity to load different amounts of light-absorbing dyes to demonstrate the continuous change in the emission color from green to red. The porosity of the mesoporous silica nanoshell was carefully controlled by varying the reaction time and stoichiometry of the organically modified silica method. Our strategy will open an avenue for advanced applications like multiplexed bioreporters for bioimaging by providing an exquisitely tailored emission profile of upconversion nanoparticles.