| Summary: | Fluorescent dye 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) is used to develop a ratiometric pH indicator based on NaYF4:Yb3+/Tm3+ upconversion nanoparticles (UCNPs). HPTS was functionalized onto the UCNP surfaces via a modified co-condensation silica coating (UCNP@SiO2-HPTS). The as-prepared UCNP@SiO2-HPTS core-shell nanostructure was characterized with transmission electron microscopy, scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy (FT-IR), and photoluminescence spectroscopy. Luminescence resonance energy transfer (LRET) from NaYF4:Yb3+/Tm3+ UCNP to HPTS was found to exhibit pH-sensitivity simultaneously under near-infrared (NIR) irradiation (λ = 980 nm).
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