A fiber-optic pH sensor prepared using a base-catalyzed organo-silica sol–gel Original Research Article

Fiber-optic pH sensors have been fabricated using fluorescein isothiocyanate immobilized in a base-catalyzed organo-silica sol–gel film. Hydrophilic sol–gel coatings are made by co-polymerizing tetraethylorthosilicate and silanol-terminated polydimethylsiloxane with 3-aminopropyltriethoxysilane (APTES) and/or 3-glycidoxypropyltrimethoxysilane. Unlike current techniques, which describe acid-catalyzed sol–gels, a base catalyst was found to be better suited for producing optically transparent gels when high concentrations of APTES were used. The sol–gel films are simple to make and require drying and aging times of as little as one day. pH sensors made using these gels exhibit fast response times, little or no dye leaching and good long-term stability.