Optical-magnetic bifunctional sub-20 nm β-NaYF4:Yb3+/Er3+@NaGdF4:Yb3+/Nd3+@NaGdF4 core-shell-shell nanoparticles triggered by 808 nm light

Abstract Small size optical-magnetic bifunctional upconversion nanoparticles (UCNPs) that can be effectively triggered by 808 nm exhibit distinct advantages of improved tissue penetrating depth, minimized overheating effect, possible for multimodal imaging and high clearance rate, which therefore are considered as desirable candidates for bioapplications. In this research, the 808 nm triggered sub-20 nm β-NaYF4:Yb3+/Er3+@NaGdF4:Yb3+/Nd3+@NaGdF4 active-core@active-shell@inert-shell structured UCNPs with optical and magnetic bifunctional properties were developed by seed-mediated growth method with NaOA as sodium source instead of the generally used NaOH. Through optimizing Nd3+ doping concentration and outermost NaGdF4 inert-shell thickness, the optical-magnetic bifunctional core-shell-shell structured UCNPs exhibited strong UC emission intensity and improved magnetic property. Furthermore, the core-shell-shell NPs were validated to be no cytotoxicity by cell viability assessment. Therefore, this research may open a general avenue for the synthesis of small size multifunctional UCNPs for practical bioapplications without overheating.