Temperature compensation is a key issue that must be addressed in almost all sensors and is particularly relevant to
chemical sensor systems. Although independent temperature measurement coupled with temperature calibration of the
chemical sensor can be employed to address this issue, the difficulty of accurate temperature measurement of the sensor
material remains a problem. We report here a novel solution to this issue and prove the principle in the context of
optical oxygen sensing. The measurement technique involves the use of two temperature-calibrated, fluorescence based
oxygen sensors that display different sensitivities to oxygen. The mathematical representation of this dual-element
sensor results in a system of two equations that can be solved for both oxygen concentration and temperature. A
numerical technique based on successive approximation has been developed that allows the use of non-linear calibration
equations, which accurately describe the responses of the sensor membranes used and, therefore, yield accurate values
for oxygen concentration and temperature.
The oxygen sensitive membranes in question consist of the oxygen-sensitive, fluorescent ruthenium complex, [Ru(II)-
2+), immobilised in a porous sol-gel matrix. Sol-gel matrices that
were derived from different precursors were used to yield membranes with different sensitivities. 3D calibration
surfaces were generated for both sensor membranes using a temperature-controlled flow cell, yielding calibration
equations with R2 values of > 0.9999 in both cases. This provides the system with a high degree of baseline accuracy.
The principle of operation of the system has been verified experimentally. This has significant implications for the
development of optical sensors, as the use of such a technique obviates the need for separate temperature measurement
devices such as thermistors or thermocouples. While the technique has been demonstrated here using phase fluorometric
oxygen sensors, it is applicable to a broad range of measurement situations,
Current sensor trends, such as multianalyte capability, miniaturisation and patternability are important drivers for materials requirements in optical chemical sensors. In particular, issues such as enhanced sensitivity and printablity are key in developing optimised sensor materials for smart windows for bioprocessing applications. This study focuses on combining novel sol-gel-based hybrid matrices with engineered luminescent complexes to produce stable luminescence-based optical sensors with enhanced sensitivity for a range of analytes including oxygen, pH and carbon dioxide. As well as optimising sensor performance, issues such as surface modification of the plastic substrate and compatibility with different deposition techniques were addressed. Hybrid sol-gel matrices were developed using a range of precursors including tetraethoxysilane (TEOS), methyltriethoxysilane (MTEOS), ethyltriethoxysilane (ETEOS), n-propyltriethoxysilane (PTEOS), phenyltriethoxysilane (PhTEOS), and n-octyltriethoxysilane (C8TEOS). Oxygen sensing, based on luminescence quenching of ruthenium phenanthroline complexes, has been realised with each of these hybrid materials. Furthermore, the possibility of immobilising pH-indicators for pH and carbon dioxide sensing has been investigated with some success. In the context of in-situ monitoring of bioprocesses, issues such as humidity interference as well as the chemical robustness of the multianalyte platform, were addressed.