Optical sensors, for

OT1442 A fibre optic sensor for flexible pipeline and riser integrity momtonng... 

Following the discovery that the fluorescence of metalloporphyrins is strongly quenched by oxygen57, optical sensor membranes were developed that are suitable for phosphorescent sensing of oxygen58. Table 1 summarizes fundamental articles on optical sensors for oxygen until the year 2000. 

Russell A.P., Fletcher K.S., Optical sensor for the determination of moisture, Anal. Chim. Acta 1985 170 209. 

Munkholm C., Walt D.R., Milanovich F.P., A fiber-optic sensor for carbon dioxide... 

Kawabata Y., Kamichika T., Imasaka T., Ishibashi N., Fiber-optic sensor for carbon dioxide with a pH indicator dispersed in a poly(ethylene glycol) membrane, Anal. Chim. Acta 1989 219 223. 

Stangelmayer A., Klimant I., Wolfbeis O.S., Optical sensors for dissolved sulfur dioxide, Fresenius J. Anal. Chem. 1998 362 73. 

Offenbacher H., Wolfbeis O.S., Ftirlinger E., Fluorescence optical sensors for continuous determination of near-neutral pH values, Sensors Actuat. 1986 9 73. 

Gautier S.M., Blum L.J., Coulet P.R., Multifunction fiber-optic sensor for the bioluminescent flow determination of ATP or NADH, Anal. Chim. Acta 1990 235 243. 

Peterson J.I., Vurek G.G., Fiber-optic sensors for biomedical applications, Science 1984 224 123. 

Lobnik A., Cajlakovic M., Sol-gel based optical sensor for continuous determination of dissolved hydrogen peroxide, Sensors Actuators B 2001 74 194-199. 

Figure 4. Luminescence decay profile of an oxygen indicator dye excited by a short flash of light, in (a) solution and (b) embedded into a gas-permeable film used to fabricate fiber-optic sensors for such species. The logarithmic scale of the Y-axis allows to compare the exponential emission decay in homogeneous solution and the strongly non-exponential profile of the photoexcited dye after immobilization in a polymer matrix.

Krska R., Kellner R., Schiessl U., Tacke M. and Katzir, Fiber optic sensor for chlorinated hydrocarbons in water based on infrared fibers and tunable diode lasers, Appl. Phys. Lett., 1993 63 (14), 1868-1871 A. 

Biirck J., Mayer J., Zimmermann B., Aache H.-J., Integrated optical sensor for chemical analysis based on near-inlfared evanescent wave absorbance measurements, SPIE, 1995 2508 243-252. 

Gauglitz G. and Ingenhoff J., Integrated optical sensors for halogenated and non-halogenated hydrocarbons, Sensors Actuator B 1993 11 207-212. 

Probably the best optical sensors for pH are based on a pH indicator dye covalently immobilized on transparent cellulose membranes (Table 15). The pKa of the dye is 7.34 and colour changes from yellow to purple are observed upon deprotonation. The cellulose membrane exhibits still more than 50% of the initial colouration after two years of storage in distilled water at ambient light. 

The majority of optical sensors for neutral (uncharged) species is based on indicators which selectively interact with the analyte and additionally give optical signal changes. Since the diffusion of neutral analytes is not as strongly affected by the polymer matrix as it is in the case of ions, all types of polymer matrices can be used. 

Optical sensors for oxygen are among the few sensors, which have found practical application for process-monitoring and clinical diagnostics. They are generally based on compounds such as platinum porphyrins or ruthenium phenanthroline derivatives (Table 17) which show a decrease in luminescence upon exposure to molecular oxygen15. 

Mohr G.J. and Wolfbeis O.S., Optical sensors for a wide pH range based on azo dyes immobilized on a novel support, Analytica Chimica Acta 1994 292 41-48. 

The members of Wolfbeis team constructed an optical sensor for ammonia-based on ion pairing76. They immobilized pH-sensitive dye (bromophenol blue) as an ion pair with cetyltrimethylammonium bromide (CTABr) in a silicone polymer matrix. Bromophenol blue, while contact the ammonia (both in water as well as in gaseous form) changes its color reversibly from yellow to blue. The immobilized dye shows long wave absorption with a good photostability. 

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. 

Optical sensors for oxygen measurement are attractive since they can be fast, do not consume oxygen and are not easily poisoned. The most common method adopted in construction is based on quenching of fluorescence from appropriate chemical species. The variation in fluorescence signal (I), or fluorescence decay time (x) with oxygen concentration [O2] is described by Stem-Volmer equation91 ... 

Wang E., Chow K., Kwan V., Chin T., Wong C., Bocarsly A., Fast and long term optical sensor for pH based on sol-gel, Anal. Chim. Acta 2003 495 45-50. 

Grant S.A., Glass S.R., A sol-gel based fiber optic sensor for local blood pH measurements, Sensors andActuat. B 1997 45 35. 

Preininger, Claudia, Sauer, Ursula., Design, quality control and normalization of biosensor chips, In Optical Sensors for Inductrial, Environmental and Diagnostic Applications, Otto S. Wolfbeis, Rainer Narayanaswamy, ed. Springer, 2003. 

Wolfbeis O.S., Fluorescence-based optical sensors for biomedical applications, In Scheggi A.M.V., Martelluci, S., Chester, A.N., Pratesi, R. (Eds.), Biomedical Optical Instrumentation and laser-Assisted Biotechnology, Kluwer Academic Publishers, 1996, p.327-337. 

Butler, M.A., Fiber optic sensor for hydrogen concentrations near the explosive limit, Journal of Electrochemical Society, 46(138), L46,1991. 

Here, I is the received radiation intensity, I0 is the source intensity, a is the absorption coefficient, c stands for the concentration of the gas to be measured and the length of the radiation pathway filled with gas is called l. Fig. 3.16 shows an optical sensor for detecting C02. 

Giordano, M. Russo, M. Cusano, A. Mensitieri, G., An high sensitivity optical sensor for chloroform vapours detection based on nanometric film of 5 form syndiotactic polystyrene, Sens. Actuators B 2005, 107, 140 147... 

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