Danielle Marie Henrie Wettling

Sol-gel-derived optical pH sensors

The sol-gel process has been successfully used for preparing amorphous and transparent oxide materials doped with organic molecules. This paper reports on the possibility of using sol-gel materials as host matrices for organic dyes in order to perform optical pH sensors. Different materials have been investigated so as to study the influence of some characteristics (porosity, hydrophilicity, hydrophobicity...) on the dye optical behavior. Results will be presented for microporous silica and heteropolysiloxanes which are organic/inorganic composites materials obtained from ormosil precursors known to provide versatile systems. Preliminary experiments have been carried out with sol-gel thin films doped with fluorescein as pH indicator and coated onto flat glass substrates. Dynamic range and response time curves are reported for the different sensors. Problems of signal losses (leachability, dye degradation...), sensor lifetime and dye stability within the different matrices are also discussed.