Optically Transparent Polyelectrolyte − Silica Composite Materials:  Preparation, Characterization, and Application in Optical Chemical Sensing

A series of polyelectrolyte-containing silica composite materials have been prepared by sol−gel processing. These optically transparent composites have been characterized by scanning electron microscopy and UV−visible spectrophotometry. These materials can be processed into monolithic disks and thin films. The thicknesses of spin-coated films of these materials on glass can be varied from 0.13 to 3.5 μm as determined by an optical interference method. These materials are ion exchangeable and less brittle than the parent silica glass due to the incorporation of the organic polyelectrolyte. These new composites retain the nanoscale porosity and optical transparency into the ultraviolet of the parent silica sol−gel glasses, making them attractive host matrixes for the immobilization of ionizable dye molecules and chemical reagents. An optical pH sensing platform (0.9 × 2.5 cm) based on the electrostatic immobilization of HPTS (8-hydroxy-1,3,6-pyrenetrisulfonic acid trisodium salt) in a PDMDAAC (poly(diallyldimethylammonium chloride))−silica composite film was fabricated and evaluated. The results clearly demonstrate that this platform is easy to construct with high batch reproducibility and can be regenerated by simple solution ion exchange. The platform is usable in both the modes of absorption and fluorescence, making it versatile. Having a fast response time (ca. ∼2 s to more than 2 units of pH change), the platform is also highly resistant to dye leaching and storage degradation over a period of months.