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Abstract. Fiber-optic sensors were developed for monitoring dissolved carbon dioxide in water samples in the 0 to 900 ppm concentration range. A pH-sensitive fluorescent dye (HPTS) was reacted with a cationic quaternary ammonium salt to form an ion pair which was electrostatically bound to the surface of particles of aminocellulose which then were dispersed into a gas-permeable silicone polymer. The green fluorescence of the base form was monitored using a fiber optic fluorometer. The use of the aminocellulose enhanced the stability and lifetime of the sensor and also increased the fluorescence of the sensor membrane because the particles act as scattering centers. The characteristics of the sensors are described with respect to dynamic range, reproducibility, long-term stability and temperature dependence.

Optical fluorescence sol-gel sensors have been developed for the detection of carbon dioxide gas in the 0.03-30% range with a detection limit of 0.008% (or 80 ppm) and a quantitation limit of 0.02% (or 200 ppm) CO(2). Sol-gels were spin-coated on glass slides to create an organically modified silica-doped matrix with the 1-hydroxypyrene-3,6,8-trisulfonate (HPTS) fluorescent indicator. The luminescence intensity of the HPTS indicator (513 nm) is quenched by CO(2), which protonates the anionic form of HPTS. An ion pair technique was used to incorporate the lipophilic dye into the hydrophilic sol-gel matrix. TiO(2) particles (<5 microm diameter) were added to induce Mie scattering and increase the incident light interaction with the sensing film, thus increasing the signal-to-noise ratio. Moisture-proof overcoatings have been used to maintain a constant level of water inside the sensor films. The optical sensors are inexpensive to prepare and can be easily coupled to fiber optics for remote sensing capabilities. A fiber-optic bundle was used for the gas detection and shown to work as part of a multianalyte platform for simultaneous detection of multiple analytes. The studies reported here resulted in the development of sol-gel optical fluorescent sensors for CO(2) gas with sensitivity below that in the atmosphere (ca. 387 ppm). These sensors are a complementary approach to current FT-IR measurements for real-time carbon dioxide detection in environmental applications.

In this study, molecularly imprinted polymers (MIPs) prepared using a multifunctional and a monofunctional monomer were compared with respect to their affinities, selectivities, and imprinting efficiencies for organophosphates. This is of interest because multifunctional monomers have higher affinities than traditional monofunctional monomers for their target analytes and thus should yield MIPs with higher affinities and selectivities. However, polymers containing multifunctional monomer may also have a higher number of unselective, non-templated binding sites. This increase in background binding sites could lead to a decrease in the magnitude of the imprinting effect and in the selectivity of the MIP. Therefore, phosphate selective imprinted and non-imprinted polymers (NIPs) were prepared using a novel multifunctional triurea monomer. The binding properties of these polymers were compared with polymers prepared using a monofunctional monourea monomer. The binding affinities and selectivities of the monomers, imprinted polymers, and NIPs were characterized by NMR titration, binding uptake studies, and binding isotherms. MIPs prepared with the triurea monomer showed higher binding affinity and selectivity for the diphenylphosphate anion in organic solvents than the MIPs prepared with the monofunctional monomer. Surprisingly, the binding properties of the NIPs revealed that the polymers prepared using the multifunctional and monofunctional monomers were very similar in affinity and selectivity. Thus, the multifunctional monomers increase not only the affinity of the MIP but also enhance the imprinting effect.

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