Ratiometric pH Sensor Based on Fluorescent Core-Shell Nanoparticles

This paper describes the preparation of fluorescent core-shell composite nanoparticles (NPs) that enable ratiometric pH measurements in a biologically relevant pH-range. The core of the composite NPs, which was used as the reference, consisted of Y2O3:Eu3+, which exhibited strong red fluorescent emission. A pH-sensitive fluorescein isothiocyanate (FITC) dye was incorporated in the outer amorphous silica shell as a pH indicator. The outer silica shell layer with FITC exhibited excellent fluorescent responses to pH, while the relative fluorescence intensity of Y2O3:Eu3+ was independent of the pH. Spectral characterization of the composite NPs by photoluminescence spectroscopy revealed good pH sensitivity with no significant differences over a relatively long period of time.