Development of a LED-based phase fluorimetric oxygen sensor using evanescent wave excitation of a sol-gel immobilized dye

doi:10.1016/0925-4005(95)01687-2

Sensors and Actuators B: Chemical

Volume 29, Issues 1–3, October 1995, Pages 226-230

https://doi.org/10.1016/0925-4005(95)01687-2 Get rights and content

Abstract

In this paper we report preliminary results from an intrinsic fibre-optic oxygen based on phase fluorimetry. Phase fluorimetry is a method of measuring the luminescence lifetime of a fluorophore and, where suitable, has many advantages over other reported optical sensing techniques such as absorption and fluoresecnece intensity monitoring. Lifetime measurements are absolute quantities, which offer the possibility of inherent referencing, and are usually independent of indicator concentration, photobleaching the excitation source intensity. The long excited-state lifetime of ruthenium polypyridyl complexes are efficiently quenched by oxygen. Sol-gel immobilization of the ruthenium complex (Ru^II-tri(4,7-diphenyl-1,10-phenanthroline)) on a multimode optical fibre yields highly durable, inert, microporous claddings which exhibit almost complete quenching under evanescent-wave excitation. The fluorophore decay curve exhibits a double exponential behaviour consisting of a fast and a slow component, both of which undergo quenching on exposure to oxygen. These data are used to model and expected behaviour of the sensor in phase fluorimetric mode. The predictions are in close agreement with experimental measurements performed with the coated fibre under blue light-emitting diode (LED) excitation. An optimum modulation frequency is identified and the performance of the intrinsic oxygen sensor in real-time measurement mode is reported. The use of an inexpensive light source, combined with a simple fabrication technique and the advantages of the phase fluorimetric method, facilitates the production of low cost, high performance optical oxygen sensors.

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Therefore, optical DO sensors based on lifetime measurement is more attractive because this parameter is an intrinsic property and independent of fluctuations in the excitation light source, changes in optical system, sensitivity of the photodetector, and photobleaching [17–19]. Nevertheless, direct lifetime measurement requires expensive high-speed electronics, fast pulsed optical sources, exact synchronization of all components, and complex data processing [20–22]. These obstacles make it difficult to employ lifetime-based DO sensor for on-site detection of DO in field.
A simple and robust integrated handheld optical fiber dissolved oxygen (DO) sensor was developed based on a compact optical structure and phase shift measurement principle. In this device, a 1 × 4 multi-mode optical fiber bundle structure was used for the transmission of excitation light and the collection and transmission of fluorescence. The fiber optode was fabricated by coating an O₂ sensing foil on the end of the optical fiber bundle. This elegant optical design significantly improved the optical transmission efficiency, miniaturization, portability, and stability of the entire sensor system. A low-cost photodetector (PD) was applied for simultaneous detection of the fluorescence signal and reference light signal based on the time-resolved effect. Rapid and accurate measurement of the phase shift between the fluorescence and reference light signals was achieved using phase measurement electronics and signal processing system. Based on a proposed theoretical model with temperature compensation calibration, this DO sensor was used for rapid, accurate, and reproducible detection of DO concentrations with long-term stability and low drift. The results of in-situ/on-line detection for various water samples were highly consistent with those of commercial optical oxygen sensors. The proposed DO sensor has the potential to be a powerful alternative to traditional oxygen sensors in laboratory or in field.
Fiber optic sensor designs and luminescence-based methods for the detection of oxygen and pH measurement
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Optical, and especially fiber optic techniques for chemical sensing have become very attractive in recent decades for a wide variety of biomedical and industrial processes and considerable progress in research in this field has been seen, evidenced by the significant number of papers published over several decades, commercial products developed and marketed and which continuing to be produced. This work extends the body of knowledge in the field and focuses on two industrially-important ‘chemical’ measurands: the determination of pH level and oxygen concentration (O₂) - both are critically important for a broad range of applications globally, in fields as diverse at the life sciences, environmental monitoring, biomedical research and thus widely across industry.
The many different optical platform designs and fabrication methods that have been developed are considered, including those for commercial applications, recognizing the wide range of industrial and scientific uses, and their performance compared. Further, the effect of specific fiber structures on sensor performance, e.g. on sensitivity, response time and long-term stability, and possible applications also has been analyzed. Applications are seen in difficult and ‘niche’ measurement environments to which conventional sensors are often not well suited, taking advantage of their lightweight nature, ease of miniaturization, potential to be multiplexed and low cost. Through a discussion of representative techniques that have reached commercial development, a comprehensive and state-of-the-art view of this exciting and important field is possible.
Optical fiber oxygen sensor utilizing a robust phase demodulator
2017, Measurement: Journal of the International Measurement Confederation
Measuring the phase shift of luminescence is always used to achieve oxygen concentration detection. A robust phase demodulator is proposed in this paper to measure luminescent phase, overcoming common faults of bad SNR in optical fiber oxygen sensor. Its phase detection linearity of 0.99999 R-square is calibrated by a commercial lock-in amplifier (Model 7230). Modulation frequency of 16 kHz is used in the oxygen measurements and a phase resolution of 0.02° is achieved by the demodulator. Phase noises of 0.03, 0.06, 0.08 and 0.1° were measured in different oxygen levels of 0.99%, 3%, 5% and 8% in experiments. A resolution of better than ±0.005% in 0.99% O₂ is realized. In addition, the demodulator which is simple but robust can be used in many luminescence phase based applications.
A new optical sensor for sensing oxygen based on phase shift detection
2016, Sensors and Actuators, B: Chemical
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Further, although the total phase shift is only 26° over the entire oxygen concentration range, the phase shift and performance are comparable to those of other sensors (see Table 1). Phase resolution based on lock-in amplifiers requires high-speed optoelectronic modulation hardware and a signal processing unit with wide bandwidth [26,31,33,34]. Although a sinusoidally modulated powered LED has been used [26,27,31–37], the signal processing unit of these devices needs to be improved.
A simple signal processing, low-cost technique for the fabrication of an optical oxygen sensor based on phase shift detection is described. The sensing film is based on the oxygen-sensing dye platinum tetrakis pentrafluoropheny porphine (PtTFPP) embedded in a polymer matrix. The feasibility of coating a photodiode with the oxygen-sensing film to fabricate an optical sensing device is investigated. The optical oxygen sensor is tested with regard to monitoring excitation voltage and oxygen concentration. The experiment results show that the maximum phase difference between 0% and 100% gaseous oxygen is 26°.
A preparation procedure for coating photodiodes with the oxygen-sensing film that produces repetitive and reliable sensing devices is proposed. The developed optical oxygen sensor is low-cost, has simple signal processing, and lacks optical filter elements. The proposed sensor is a cost-effective alternative to traditional electrochemical-based oxygen sensors and provides a platform for other optically based sensors.
The effects of different sterilization procedures on the optical polymer oxygen sensors
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The supporting polymer matrix for the indicator should comprise high permeability for oxygen, adequate mechanical and chemical stability and high solubility for the indicator. The polymers commonly used for optical oxygen sensors are various polystyrenes [12,13,25], cellulosic materials [11,23,24], polysulfones [20,21], siloxanes [10,22], hydrogels [19], sol–gel matrices [14,15,26–29], etc. Numerous fields in which optical oxygen sensors are applied require sterile environment and consequently sterile sensors.
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Citation Excerpt :
Optical sensing, based on the quenching of luminescence emitted by a luminophore sensitive to a given analyte, has become increasingly popular over the last two decades, and currently is a widely used approach for the fabrication of optical sensors [24–26]. Optical methods for the determination of dissolved or gaseous oxygen are mainly based on this principle [20], and a variety schemes based on the measurement of the emission intensity or luminescence lifetime have been reported in the literature in recent years [8,17–19,27–30]. However, while intensity measurements are relatively simple and accurate in the laboratory [31–34], they are often inadequate in real-world applications due to their dependence on the intensity of the exciting light, detector drift, degradation or leaching of the dye, light losses in the optical path, orientation and location of the sensor, concentration of the luminophore, or optical surface quality.
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Invited and regular paperDevelopment of a LED-based phase fluorimetric oxygen sensor using evanescent wave excitation of a sol-gel immobilized dye

Abstract

Anal. Chim. Acta

Fibre optic oxygen sensor based on fluorescence quenching of evanescent-wave excited ruthenium complexes in sol-gel derived porous coatings

Analyst

Fiber-optic fluoresensor for oxygen and carbon dioxide

Anal. Chem.

Determination of oxygen concentrations by luminescence quenching of a polymer-immobilized transition-metal complex

Anal. Chem.

LED-based fibre optic oxygen sensor using sol-gel coating

Electron. Lett.

Invited and regular paper
Development of a LED-based phase fluorimetric oxygen sensor using evanescent wave excitation of a sol-gel immobilized dye