Preparation of A Novel Type of Fluorescein Isothiocyanate-Doped Fluorescent Silica Nanoparticle and Its Application as pH Probe

In this study, a novel type of core-shell fluorescein isothiocyanate (FITC)-doped fluorescent silica nanoparticle was synthesized and used as an intracellular pH sensor. First, a silane reagent of 3-aminopropyl-trimethoxysilane (APTMS) was used to synthesize a novel precursor FITC-APTMS. Then, FITC-APTMS/SiO2 (FAS) nanoparticles were obtained using water-in-oil (W/O) microemulsion technique in the presence of tetraethoxysilane (TEOS). Characterizations by transmission electron microscopy (TEM) and fluorescence spectroscopy show that the nanoparticles are spherical, monodisperse, and uniform in size with the diameters being (150 ± 15) nm. They are also highly fluorescent and highly photostable. When the nanoparticles were dispersed in aqueous solution under ultrasonic treatment for 6 h, no obvious dye leaking was observed. It was found that the fluorescence of the nanoparticles was pH sensitive, and the pH response range was 3.6–9.7, with a linear range of pH 6.0–9.0. The FAS nanoparticles could be phagocytosed by murine neural stem cell and thus could be applied to detect intracellular pH value of single cell.