Activatable Rare Earth Near-Infrared-II Fluorescence Ratiometric Nanoprobes

Rational design of efficient lanthanide-doped down-shifting nanoparticles (DSNPs) has attracted tremendous attention. However, energy loss was inevitable in the multiple Ln³⁺ doping systems owing to complex energy migration processes. Here, an efficient NaErF₄@NaYF₄@NaYF₄:10%Nd@NaYF₄ DSNP was tactfully designed, in which a buffer layer of NaYF₄ was modulated to restrict the interionic energy migration between Er³⁺ and Nd³⁺; meanwhile, the surface defects were passivated by an outermost layer of NaYF₄. Therefore, the as-prepared DSNPs exhibited two intensive near-infrared-II fluorescence emissions of 1525 nm from Er³⁺ and 1060 nm from doped Nd³⁺ under 808 nm excitation. Further, a novel ratiometric nanoprobe NaErF₄@NaYF₄@NaYF₄:10%Nd@NaYF₄@A1094 was fabricated by coupling an organic dye of A1094 onto the DSNP surface to quench the 1060 nm emission by the efficient Förster resonance energy transfer, while emission at 1525 nm retained. Thereafter, these activatable ratiometric nanoprobes were used for rapid and sensitive detection of peroxynitrite (ONOO^-) in vivo.