We report on the development of a novel optical oxygen sensor for breath monitoring applications using the technique of phase fluorometry. The principal design criteria are that the system be compact, lightweight, and employ a disposable sensing element (while performing competitively with current commercial analyzers). The oxygen-sensitive, luminescent ruthenium complex Ru[dpp] is encapsulated in a sol-gel matrix and deposited onto a custom-designed, polymer sensor chip that provides significantly improved luminescence capture efficiency. The performance of the sensor module is characterized using a commercially available lung simulator. A resolution of 0.03% O2 is achieved, which compares well with commercial breath monitoring systems and, when combined with its immunity to humidity and ability to respond effectively across a broad range of breathing rates, makes this device an extremely promising candidate for the development of a practical, low-cost biodiagnostic tool.
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.
In the last three years, a number of Irish primary schools have been using LEGO Mindstorms technology in order to investigate the use of project-based learning as an alternative teaching tool. This has involved the use of LEGO bricks combined with standard electronic motors and some commercial sensors (e.g. temperature). In order to develop this project into the area of science education, we have developed a range of miniaturized optical sensors, which are compatible with the LEGO platform. This paper describes two such sensors that have been developed and fabricated for use with the LEGO platform, a collaboration between the MIT Media Lab and the National Centre for Sensor Research. In particular a working oxygen sensor has been designed and fabricated. The principal design features were compatibility with the programmable LEGO platforms and robustness for classroom use. This sensor uses the method of intensity quenching to determine oxygen concentration. In addition, simple color sensors have been produced. The aim of developing such sensors is to familiarize students with the concept of colour detection and to introduce them to the basic principles of spectroscopy. The performance of both sensor types and preliminary classroom results are reported.
Modified Atmosphere Packaged (MAP) food employs a protective gas mixture, which normally contains selected amounts of carbon dioxide (CO2) and oxygen (O2), in order to extend the shelf life of food. Conventional MAP analysis of package integrity involves destructive sampling of packages followed by carbon dioxide and oxygen detection. For quality control reasons, as well as to enhance food safety, the concept of optical on-pack sensors for monitoring the gas composition of the MAP package at different stages of the distribution process is very attractive. The objective of this work was to develop printable formulations of oxygen and carbon dioxide sensors for use in food packaging. Oxygen sensing is achieved by detecting the degree of quenching of a fluorescent ruthenium complex entrapped in a sol-gel matrix. In particular, a measurement technique based on the quenching of the fluorescence decay time, phase fluorometric detection, is employed. A scheme for detecting CO2 has been developed which is compatible with the oxygen detection scheme. It is fluorescence-based and uses the pH-sensitive 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) indicator dye encapsulated in an organically modified silica (ORMOSIL) glass matrix. Dual Luminophore Referencing (DLR) has been employed as an internal referencing scheme, which provides many of the advantages of lifetime-based fluorometric methods. Oxygen cross-sensitivity was minimised by encapsulating the reference luminophore in dense sol-gel microspheres. The sensor performance compared well with standard methods for both oxygen and carbon dioxide detection. The results of preliminary on-pack print trials are presented and a preliminary design of an integrated dual gas optical read-out device is discussed.
A dissolved oxygen sensor, based on sol-gel-derived silica thin films impregnated with an oxygen-sensitive ruthenium complex, is reported. Porous sol-gel silica films, dipcoated onto either planar glass substrates or declad optical fibers, are doped with the complex [RuII-tris(4,7-diphenyl-1,10-phenanthroline)], whose fluorescence emission is quenched by oxygen. The complex is entrapped in the cage-like structure of the sol-gel matrix, but is accessible to oxygen via the microporous channels. This work compares the difference in oxygen quenching response between gas phase and aqueous phase measurements. Optimization of dissolved oxygen response by tailoring of the film fabrication parameters is reported. Using a high-brightness blue LED, combined with a miniature photodiode-based detection system, these results establish the viability of a low-cost, high-performance, portable optical dissolved oxygen sensor.
Two evanescent wave fiber optic sensors for oxygen are reported: one intensity based and the other based on phase fluorimetry. Both sensors employ the quenching by oxygen of the fluorescence from a ruthenium complex trapped in the cagelike structure of a sol-gel-derived porous film on a declad section of multimode optical fiber. The sensors exhibit excellent performance using excitation from new high brightness blue LEDs and establish the viability of low-cost portable sensor devices based on the 501-gel process.
Two evanescent wave fiber optic sensors for oxygen are reported: (i) intensity-based, and (ii) based on phase fluorimetry. Both sensors employ the quenching by oxygen of the fluorescence form a ruthenium complex trapped in the cage-line structure of a sol-gel-derived porous film on a declad section of multimode optical fiber. The sensors exhibit excellent performance using excitation from new high brightness blue LEDs and establish the viability of low-cost portable sensor devices based on the sol-gel process. The data presented for the intensity-based sensor were obtained using an all solid state excitation and detection system. Preliminary results obtained by application of the intensity- based sensor to dissolved oxygen measurement are also reported.
In this paper an overview is presented of the state-of-the-art of optical sensors which employ sol-gel-derived coatings. The technique is particularly suited to the side-coating of optical fibers or waveguides in evanescent-wave sensors because precise control of sensitivity- determining parameters, such as the coating thickness and length, is achievable. Sensors based on entrapped organic and inorganic dyes, enzymes and other biomolecules have been reported. The main features of the process are illustrated by examples of chemical sensors and biosensors from the literature. In particular, the development of an oxygen sensor based on the quenching of fluorescence from a sol-gel-entrappd ruthenium complex is described. This sensor may be operated in intensity or decay-time mode. The latter offers many advantages over intensity-based sensing and may also be used to provide useful diagnostic information concerning the distribution/accessibility of the sensor fluorophore. Issues which require further investigation before this technology can proceed to the stage of industrial development are also highlighted.
The ability to determine oxygen concentration is of great importance for many industhal, medical and
environmental applications. Optical oxygen sensors are attractive because of their many advantages over other
sensor types, in that they offer the possibility of miniaturization, have fast response times, do not consume
oxygen, and are not easily poisoned.