Two-Dye Core/Shell Zeolite Nanoparticles: A New Tool for Ratiometric pH Measurements

The preparation of core/shell nanoparticles that enable ratiometric pH measurement is described. The core of the nanoparticles consists of azeolite-beta matrix that exhibits a 3-hydroxyflavone reference dye within the porous network. Coating an amorphous silica shell containing a fluorosensor around the zeolite through the Stober process provides pH sensitivity to the nanoparticles. Morphological characterization (dynamic light scattering transmission electronic microscopy) demonstrates the control of the sensing silica shell around the zeolite cores, leading to highly monodisperse spherical nanoparticles, while structural characterization (wide-angle X-ray diffraction, nitrogen adsorption) shows the amorphous character of the shell. Spectral characterization via UV/Vis absorption and steady-state fluorescence shows good pH sensitivity of the resulting nanosensors with a pK(a) suitable for bioanalytical applications.