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,
The major trends driving optical chemical sensor technology are miniaturisation and multi-parameter functionality on a single platform (so-called multi-analyte sensing). A multi-analyte sensor chip device based on miniature waveguide structures, porous sensor materials and compact optoelectronic components has been developed. One of the major challenges in fluorescence-based optical sensor design is the efficient capture of emitted fluorescence from a fluorophore and the effective detection of the signal. In this work, the sensor platform has been fabricated using poly(methyl methacrylate), PMMA, as the waveguide material. These platforms employ a novel optical configuration along with rapid prototyping technology, which facilitates the production of an effective sensor platform.
Sensing films for oxygen, carbon dioxide and humidity have been developed. These films consist of a fluorescent indicator dye entrapped in a porous immobilisation matrix. The analyte diffuses through the porous matrix and reacts with the indicator dye, causing changes in the detected fluorescence. The reaction between the dye and the analyte is completely reversible with no degradation of the signal after detection of different concentrations of the analyte. A single LED excitation source is used for all three analytes, and the sensor platform is housed in a compact unit containing the excitation source, filters and detector.
The simultaneous detection of several analytes is a major requirement for fields such as food packaging, environmental quality control and biomedical diagnostics. The current sensor chip is designed for use in indoor air-quality monitoring.