Near-infrared luminescent sugar sensor based on lanthanoid-doped upconversion nanoparticles (UCNPs)

We developed lanthanoid-doped upconversion nanoparticles (UCNPs) and attempted to apply them as wavelength conversion devices to near-infrared luminescent sugar sensors. By doping yttrium fluoride with ytterbium and thulium, UCNPs (NaYF₄: Yb/Tm) showing upconversion (UC) emission in the near-infrared region (800 nm) were synthesized. A receptor-sensitive near-infrared absorbing dye that increases the absorbance in the near-infrared region (700-800 nm) by complex formation with phenylboronic acid (PBA) as a sugar receptor was immobilized on core-shell type lanthanoid UCNPs covered with a silica layer. When fructose was added to a dye-immobilized core-shell type UCNPs dispersion solution containing a certain amount of PBA (1.0 × 10⁻³ mol L⁻¹), the UC emission intensity at 800 nm increased with increasing the concentration of fructose (0 mol L⁻¹ to 3.0 × 10⁻¹ mol L⁻¹). This result indicates that the internal filter effect between the dye and UCNPs is eliminated by a change in the absorption spectrum of the immobilized receptor-sensitive dye due to a competitive complex formation reaction accompanying the increase in the fructose concentration. And as a result, the UC emission intensity increased. It was found that when the fructose concentration was 3.0 × 10⁻¹ mol L⁻¹, the UC emission intensity increased by 14.6% compared to the case without fructose. (author)