Dual-fluorophore silica microspheres for ratiometric acidic pH sensing

Encapsulation of fluorophores in silica matrix offers many advantages such inhibition of photobleaching and possibilities for ratiometric pH sensing. Dualfluorophore pH-responsive silica microspheres, incorporating pyranine (HPTS) and rhodamine B isothiocyanate (RBITC), were synthesized by Stöber method, followed layer-by-layer depositions. The resulting dual-fluorophore silica microspheres were then characterized by SEM, TEM, fluorescence spectroscopy and imaging. The incorporation of two dyes in the microspheres allowed ratiometric quantification of pH. The ratiometric approach has been proven to reduce the influences of external perturbations and unequal dye concentration in silica matrix during measurements. The dynamic range for pH was from 1.5 to 4. The sensing microspheres could be applied to determine acidic pH. Additionally, the sensing microspheres exhibited a high colloidal and long-term stability and also allow a fast detection of pH due the porosity of the microspheres. Such structured microspheres could be optimized, using multiple dyes for multianalyte detection. [Figure not available: see fulltext.]