Fabrication of dual dye-doped silica nanotube as a fluorescent ratiometric pH sensor.

This study described a novel fabrication of fluorescence co-encapsulating silica nanotubes (F@SNT) and the further application of the as-synthesized nanostructure as a ratiometric pH sensor in buffer solution. Silica nanotubes (SNTs) embedded anodic alumina oxide (AAO) template was fabricated by sol-gel technique, tetramethyl rhodamine (TMR-the reference dye) was incorporated directly onto silica layer via hydrophobic interaction. Subsequently, fluorescent isothiocyanate (FITC-pH sensitive dye) was encapsulated inside poly-dimethylsiloxane (PDMS) matrix and the FITC-PDMS nanocomposite was doped into the hollow structure of SNT using nano-molding lithography. On removing AAO, free-standing SNTs were obtained and were subsequently applied as a ratiometric pH sensor in phosphate buffer solution. The dual dye-doped SNTs showed excellent fluorescence and a good pH sensing performance from pH 5.2-8.0. The results were distinguishable by the emission spectra and by fluorescent visualization. High photostability, sensitivity, biocompatibility with adjustable sizes make dual dye doped-SNT a promising nanostructure for bioapplications.