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1 Materials Science Poland

1 2007

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Novel sol-gel derived films for luminescence-based oxygen and pH sensing

Wencel D., Higgins C., Klukowska A., Maccraith B. D., Mcdonagh C.

Materials Science Poland

2007

Vol. 25, No. 3

767--779

A range of both sol-gel and polymer derived sensor films have been developed for optical oxygen and pH sensing. Oxygen sensing is based on the luminescence quenching of the ruthenium complex [Ru(II)-tris( 4,7-diphenyl-1,10-phenanthroline)]dichloride, ([Ru(dpp)3]2+), which is entrapped in the sol-gel matrix. The oxygen-dependent luminescence is detected using the principle of phase fluorometry, which facilitates indirect monitoring of the luminescence lifetime. The pH sensor uses excitation ratiometric detection of the fluorescence from the pH sensitive dye, 1-hydroxypyrene-3,6,8-trisulfonic acid, ion-paired with cetyl trimethyl ammonium bromide (HPTS_IP). The phase-based detection scheme, dual lifetime referencing (DLR), was also examined as an alternative sensing strategy. ORMOSIL oxygen sensor films were fabricated using a range of organosilicon precursors including methyltriethoxysilane (MTEOS), ethyltriethoxysilane (ETEOS), n-propyltriethoxysilane (PTEOS) and phenyltriethoxysilane (PhTEOS). In addition to optimising the sensor performance, issues such as the influence of humidity on oxygen sensing were addressed. By varying the processing parameters, the surface characteristics and microstructure were tailored to suit applications such as breath gas analysis and bioprocess monitoring. pH sensor films were prepared by hydrolyzing and co-condensing (3-aminopropyl) trimethoxysilane (APTMS) with an organosilicon monomer such as ETEOS or PTEOS or the polymer, ethyl cellulose (EC). Optimised pH sensors showed good reproducibility, reversibility and short response times. The dynamic range for these sensor films extends from pH 6.00 to 8.50 which is relevant for bioprocess monitoring applications. The spectral compatibility of the luminophores and the printability of the sol-gels present the possibility of simultaneous oxygen and pH sensing using low-cost LEDs as excitation sources along with common detection electronics.