Fiber optic evanescent wave sensor

A novel fiber optic sensor concept using antibody-antigen reactions at a glass-liquid interface was reported by Daehne146. The reaction of antibodies immobilized onto the surface of fused silica fiber optic or planar waveguides with antigens in solution was detected by interaction with the evanescent wave. By detecting in-line fluorescence, the measurement of human IgG is described. 

S. Sekimoto, H. Nakagawa, S. Okazaki, K. Fukuda, S. Asakura, T Shigemori, and S. Takahashi, A fiber-optic evanescent-wave hydrogen gas sensor using palladium-supported tungsten oxide. Sensors Actuators B 66(1-3), 142-145 (2000). 

Seo et al. (1999) used a planar optic biosensor that measures the phase shift variation in refractive index due to antigen binding to antibody. In this method, they were able to detect S. enterica serovar T) himurium with a detection limit of 1 x 10 cfu/ml. When chicken carcass fluid was inoculated with 20 cfu/ml, the sensor was able to detect this pathogen after 12 h of nonselective enrichment. A compact fiber optic sensor was also used for detection of S. T) himurium at a detection limit of 1 X 10" cfu/ml (Zhou et al., 1997, 1998) however, its efficacy with food samples is unproven. Later, Kramer and Lim (2004) used the fiber optic sensor, RAPTOR , to detect this pathogen from spent irrigation water for alfalfa sprouts. They showed that the system can be used to detect Salmonella spiked at 50 cfu/g seeds. An evanescent wave-based multianalyte array biosensor (MAAB) was also employed for successful testing of chicken excreta and various food samples (sausage, cantaloupe, egg, sprout, and chicken carcass) for S. T) himurium (Taitt et ah, 2004). While some samples exhibited interference with the assay, overall, the detection limit for this system was reported to be 8 x 10 cfu/g. 

DeMarco DV, Lim DV (2001) Direct detection of escherichia coliol57 h7 in unpasterized apple juice with an evanescent wave sensor. J Rapid Meth Automation Micro 9 241-257 Diez A, Andres MV, Cruz JL (2001) In-line fiber-optic sensors based on the excitation of surface plasma modes in metal-coated tapered fibers. Sensors Actuators B Chem 73 95-99 Dostalek J, Ctyroky J, Homola J, Brynda E, Skalsky M, Nekvindova P, Spirkova J, Skvor J, Schrofel J (2001) Surface plasmon resonance biosensor based on integrated optical waveguide. Sensors Actuators B Chem 76 8-12... 

Current research is now directed towards realizing a miniaturized sensor by using integrated optics technology and planar waveguide structures. The construction of planar evanescent wave absorbance sensors offers some advantages compared to the existing fiber-optic sensor ... 

Optical biosensor technology has realized remarkable developments in the last decades [126-129]. This section will specifically focus on IR fiber sensors based on ChG materials. We will first describe the mechanism of evanescent wave spectroscopy and summarize the essential properties of ChG glasses when used in the framework of fiber-based sensing. Finally we will present several techniques commonly employed for the shaping of ChG glasses into fiber-optic sensors and survey their applications. 

Messica A., Greenstein A., and Katzir A., Theory of fiber-optic, evanescent-wave spectroscopy and sensors, App/. Opt, 35,2274-2284 (1996). 

Gas sensors based on sol-gel films were widely investigated for the detection of O2 [169-171], CO2, CO, H2 [172], H2S, I2, NH3, NO, and NO2 and were summarized in Refs [173,174]. Fiber-optic sensors for humidity based on evanescent wave scattering and absorption were prepared by doping the sol-gel coating with methylene blue [175]. Sensors were also developed for the determination of... 

MacCraith, B.D., Mcdonagh, C.M., Okeefe, G., Keyes, T.E., Vos, J.G., Okelly, B., and Megilp, J.F. (1993) Fiber optic sensor based on fluorescence quenching of evanescent-wave excited ruthenium complexes in sol-gel derived porous coatings. Analyst, 118, 385-388. 

Matejec V., Chomat M., Pospisilova M., Hayer M., Kasik I. Optical fiber with novel geometry for evanescent-wave sensing, Sensors Actuators (1995) B 29, pp. 416-422. 

Gupta B.D., Sharma A., Singh C.D., Fiber optic evanescent-wave absorption sensors based on uniform and tapered fibers, Proc. 2nd Europtrode (1994), Firenze, p.189. 

Sol-gel coating technique for optical chemical sensors and biosensors is now in extensive research phase. For example, the side-coating of optical fibers or waveguides in evanescent-wave sensors it is particularly important to control precisely the sensitivity determining parameters, such as the coating thickness and length45. 

The fabrication and characterization of a fiber optic pH sensor based on evanescent wave absorption was presented by Lee63. The unclad portion of a multi-mode optical fibre was coated with the sol-gel doped with pH sensitive dye. The sensitivity of the device increased when the multiple sol-gel coatings were used in the sensing region. The dynamic range and the temporal response of the sensor were investigated for two different dyes -bromocresol purple and bromocresol green. 

B.D. Gupta and D.K. Sharma, Evanescent wave absorption based fiber optic pH sensor prepared by dye doped sol-gel immobilization technique, Opt. Commun., 140(1-3) (1997) 32-35. 

A fiber-optic device has been described that can monitor chlorinated hydrocarbons in water (Gobel et al. 1994). The sensor is based on the diffusion of chlorinated hydrocarbons into a polymeric layer surrounding a silver halide optical fiber through which is passed broad-band mid-infrared radiation. The chlorinated compounds concentrated in the polymer absorb some of the radiation that escapes the liber (evanescent wave) this technique is a variant of attenuated total reflection (ATR) spectroscopy. A LOD for chloroform was stated to be 5 mg/L (5 ppm). This sensor does not have a high degree of selectivity for chloroform over other chlorinated aliphatic hydrocarbons, but appears to be useful for continuous monitoring purposes. 

OF optical fibers, IOS integrated optical sensors, A absorbance, R reflectance, F fluorescence, ev evanescent wave, ISP isopropyl alcohol, DOS bis(2-ethylhexyl)sebacate, o - NPOE ortho-nitrophenyl octyl ether, TOP tris(2-ethylhexyl)phosphate... 

Luminescent evanescent wave-based sensors use optical fibers and planar waveguides [105,106] as fight-guiding structures, and they are more complex than the absorbance ones. However, such optodes have been satisfactorily applied to measure fluorescence of indicators or labels for the measurement of gas molecules, proteins or labeled antigen-antibody interactions as well as directly in solution [24,107] when immobilized in matrices [23,109]. 

The fiber optic evanescent wave sensor (FO-EWS) belongs to a sensor in which the fiber core interacts with the analyte. This interaction occurs through the attenuated total reflection (ATR) and the evanescent wave excitation in a dielectric medium of smaller refractive index in the vicinity of fiber core. If the surrounding medium is fluorescent, then the fluorescence signal in the reaction region of evanescent wave field is excited and detected. This is illustrated in Figure 8.2. 

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