Optical CO2 sensors

Pyruvate Corn kernei Pyruvate decarboxyiase CO2 gas sensor, fiber-optic CO2 sensor... 

Amao, Y. Komori, T. Optical CO2 sensor of the combination of colorimetric change of a-naphthol-phthalein in poly(isobutyl methacrylate) and fluorescent porphyrin in polystyrene. Talanta 2005, <56, 976-981. 

Amao Y (2003) Probes and polymers for optical sensing of oxygen. Mikrochim Acta 143 1-12 Amao Y, Nakamura N (2004) Optical CO2 sensor with the combination of colorimetric change of a-naphtholphthalein and internal reference fluorescent porphyrin dye. Sens Actuators B 100 347-351 Ando M, Kobayashi T, Haruta M (1994) Enhancement in the optical CO sensitivity of NiO film by the deposition of ultrafine gold particles. J Chem Soc Faraday Trans 90 1011-1013 Ando M, Kobayashi T, Haruta M (1995) Optical CO detection by use of CuO/Au composite films. Sens Actuators B 24-25 851-853... 

Ge, X. Rostov, Y. Rao, G. High-stability non-invasive autoclavable naked optical CO2 sensor. Biosens. Bioelectron 2003,18, 857-865. 

He, X. Rechnitz, G. A. Linear response function for fluorescence-based fiber-optic CO2 sensors. Anal. Chem. 1995, 67, 2264-2268. 

Nakamura N, Amao Y (2003) Optical CO2 sensor with the combination of colorimetric change of pH indicator and internal reference luminescent dye. Bull Chem Soc Jpn 76 1459-1462... 

An optical sensor for the measurement of carbon dioxide in modified atmosphere packaging (MAP) applications was developed89. It was based on the fluorescent pH indicator l-hydroxypyrene-3,6,8-trisulfonate (HPTS) immobilized in a hydrophobic organically modified (ormosil) matrix. The CO2 sensor was stable over a period of at least 7 months and its output was in excellent agreement with a standard reference method for carbon dioxide analysis. 

A laboratory characterisation was carried out, during which the performances of the optical fibre sensor were carefully verified and compared with those of the Tonocap. The results showed the capability of the optical fibre sensor to detect CO2 correctly even in the presence of rapid changes of the order of 1 minute. 

First clinical results were obtained by using a combined catheter which included both the optical fibre sensor and the Tonocap balloon (Figure 8) A typical result obtained on an intensive care patient, is shown in Figure 9. In the graph the tracing of the end-tidal CO2 (EtCC>2), i.e. the CO2 concentration in the expiration at the end of the expiratory phase, and the values of the arterial CO2 (PaC02), obtained from blood samples drawn from the patient, are also shown. As expected, a rapid CO2 peak was detected only by the optical fibre sensor, and was not seen by Tonocap (as in the measurements carried out on volunteers). Moreover, the optical fibre sensor seems to follow better the end-tidal CO2. 

This chapter reviews the development of optical gas sensors, starting with an initial emphasis on optical-fibre remoted techniques and finishing with a particular focus on our own group s work on highly selective methods using correlation spectroscopy. This latter section includes extensive theoretical modelling of a correlation spectroscopy method, and compares theory with practice for a CO2 sensor. 

Ertekin and coworkers developed an additional optical COj sensor based on the fluorescence signal intensity changes of the pH-sensitive fluorescent dye 8-hydroxypyrene-l,3,6-trisulfonic acid trisodium salt (HPTS) dissolved in ILs [18]. When HCO3 was added to HPTS solution, the fluorescence intensity of the peak centered around 520 nm decreased by 90% in [C4Qlm] [BF4] and by 75% in [C4Cilm]Br. The reported detection limit for CO2 (g) was 1.4% while the detection limit for dissolved COj was 10 M HCO3. The sensor exhibited excellent stability and repeatability over a time period >7 months. 

Figure 3. A block diagram showing the electro-optical components of the fast response ln-situ CO2 sensor. The illustration shows a specific arrangement of the components identified in Figure 2. Temperature controlled regions are shown within dashed lines.

Figure 4. The source containment system used in the CO2 sensor. The quartz glass dewar allows good thermal insulation of the forward portion of the source plug, thereby minimizing heat transfer from the source to the optical system.

Figure 5. A photograph of the fast response ln-sltu CO2 sensor monitoring carbon uptake by a soybean canopy. The open, folded optical absorption cell allows for fast sample exchange. The surrounding instruments measure air flow and humidity variations.

A CO2 sensor with a fiber-immobilized indicator has also been described [132]. When two sensing layers with different optical properties and selectivity of one for O2 and the other for CO2 are attached to the end of a fiber, a single sensor for both species can be obtained [52]. A cross-section through an O2/CO2 sensor layer is shown in Figure 17-22 and a typical response curve in Figure 17-23. 

The principle of the fiber-optic pH sensor led Vurek et al. [133] to devise a CO2 sensor. Instead of coupling the pH indicator dye to an insoluble polymer, a simple isotonic solution of salt, hydrogencarbonate, and dye was used, which was covered with a C02-permeable silicone-rubber membrane. The sensor s performance was demonstrated in vivo. Similarly, a fluorescein-based C02-sensitive system was reported by Hirschfeld et al. [134]. 

Optical gas sensors generally have some characteristics such as a high insulating capacity, independence of electrical noises and operation in safety. Moreover it is possible for them to detect a variety of gases by choosing a gas sensing material. For environmental use of optical sensors, applications for NO , SOj, CO2 and CO are expected. 

Fiber optic pH sensors have distinct advantages over pH electrodes. They are small, not interfered by electromagnetic flelds and have remote sensing capability. They can be used in extreme environments, such as deep-water analysis, chemical reactors, or wastewater. Moreover, they can be intrinsically referenced due to the dual wavelength measurement capabiUty and do not require a reference electrode [90]. Optical pH sensors also pave the way for imaging applications, whereas pH electrodes only enable punctiform pH measurements. Sensors for pH determination are also of high significance in environmental and marine research because they provide the basis for CO2 sensors. 

Figure 28.5 Field-deployed TDLAS spectrometer for eddy-correlation trace-gas measurements. The gas sampling head (on the left) incorporates a non-dispersive IR H2O/CO2 sensor and an anemometer. Adapted from Werle and Korman, Appl. Opt., 2001, 40 846, with permission of The Optical Society of America...

NDIR type CO2 sensors allow highly specific detection via the absorption of CO2 in the infrared region [39-41]. However, because of bulk size, limited operation temperature range (<328 K) and high cost, their applications are not widespread. The use of light emitting diode (LED) has allowed dramatic reduction in the size of the optics system allowing NDIR sensor dimension... 

The most conventional method to determine methanol crossover in a DMFC is to monitor the CO2 content in the cathode exhaust gas flux by using an optical infrared sensor, by gas chromatographic analysis, or by mass spectrometry [132], However, these measurements are based on the assumptions that flie crossed over methanol at the cathode is completely oxidized and that there is no CO2 permeation from the anode to the cathode. In reality, in particular for operation at high current density, a large amount of CO2 permeates from the anode to the cafliode in the DMFC. So far, no reliable method is available to measure the methanol crossover through the membrane from the anode to the cathode at the operating status. 

Fiber-optic chemical sensors for different analytes can be developed based on pH sensors. Gases such as CO2 and NH3 react with water and change the pH of a solution when solvated, which can be detected by a pH sensor. Gas fiber-optic chemical sensors will be discussed in the next section. Any chemical or biological species that produces either acids or bases during a chemical or enzymatic reaction can be detected by measuring the pH of the medium. 

The second type of CO2 fiber-optic chemical sensor is constructed by using ion pairs consisting of a pH indicator anion and an organic quaternary cation. First, a pH indicator dye (DH) and a quaternary ammonium hydroxide (Q OH ) are entrapped into a proton-impermeable but CO2-permeable polymer membrane, which is then immobilized onto the fiber s surface. The mechanism of this CO2 sensor is based on the interaction between the dye molecules (DH) and the quaternary cations (Q+OH ) to form hydrated ion pairs (Q D XH2O). The hydrated ion pair is dissolved in the polymer, where it reacts with CO2 according to the following reaction ... 

Marazuela MD, Moleno-Bondi MC, Orellana G (1995) Enhanced performance of a fibre-optic luminescence CO2 sensor using carbonic anhydrase. Sensor Actuat B 29 126-131... 

Nivens D., Schiza M., Angel S., Multilayer sol-gel membranesfor optical sensing applications single layer pH and dual layer CO2 and NH3 sensors, Talanta 2002 58 543-550. 

Thus pH responsive dyes or fluorophores can be used to design optical sensors for C02. To prevent pH interference, a hydrophobic membrane with high C02 permeability is used to selectively allow CO2... 

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