Evanescent wave sensor

Parriaux O., Veldhuis G.J., Normalized analysis for the sensitivity optimization of integrated optical evanescent-wave sensors, J of Lightwave Technol. 1998 16 573-582. 

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 pH measurement can by realized using sol-gel films and evanescent-wave sensors method74. To incorporate a near-infrared pH sensitive fluorescent dye, a thin-film coating on the core of a multimode fiber was used. By evanescent wave excitation an absorption or fluorescent based sensor can be realized for use in high pH regions. 

Janotta M., Karlowatz M., Vogt F., Mizaikoff B., Sol-gel based mid-infrared evanescent wave sensors for detection of organophosphate pesticides in aqueous solution, Anal. Chim. Acta 2003 496 339-348. 

As mentioned in Sect. 15.2, sometimes a 4th thin layer (M) of metal or die is incorporated between the substrate and waveguide film to decrease the radiation loss into the substrate of the substrate radiation modes. These modes are referred to as leaky modes and the obtained structure is the MCLW. This configuration is also broadly used in evanescent wave sensor systems. 

B.D. MacCraith, Enhanced evanescent wave sensors based on sol-gel-derived porous glass coatings, Sensor Actuat. B-Chem., 11(1-3) (1993) 29-34. 

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. 

Loev, W. F., Button, L. J., Slovacek, R. E. (1991) Optical Characteristics of Fiberoptic Evanescent Wave Sensor Theory and Experiment, Biosensor with Fiberoptics, the Humana Press Inc., pp.l39... 

Multianalyte detection is becoming the crucial issue for biosensing development. Many areas demand a multianalyte operation environmental screening, with thousands of samples per year to be analysed, genomics and proteomics, pharmaceutical screening, etc. Direct optical detection with evanescent wave sensors could be a possibility but a parallel detection of as many sites as possible is necessary [98]. 

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... 

Fig. 1 Schematic of evanescent wave sensor based on planar optical waveguide...

The sensitivity of the evanescent wave sensors, in particular, the guided waves, is defined by ... 

Jensen JB, Pedersen LH, Hoiby PE, Nielsen LB, Eolkenberg JR, Riishede J, Noordegraaf D, Nielsen K, Carlsen A, Bjarklev A (2004) Photonic crystal fiber based evanescent-wave sensor for detection of biomolecules in aqueous solution. Opt Lett 29 1974-1976... 

Most label-free optical bio/chemical sensors belong to the category of evanescent-wave sensors [5], in which the evanescent field exponentially decays into the surrounding medium for tens to few hundred of nanometers away from the solid sensor surface. These sensors usually utilize the RI change induced by the molecular interaction with the evanescent field as the sensing mechanism. RI change is related to the sample concentration rather than the total sample mass. Therefore, in principle, an Rl-based sensor can perform sensitive detection with small sample volumes. 

Instead of the dielectric/dielectric interface used in evanescent wave sensors, it is possible to arrange a dielectric/metal/dielectric sandwich layer such that when monochromatic polarized light (e.g., from a laser source) impinges on a transparent medium having a metalhzed (e.g., Ag or Au) surface, light is absorbed within the plasma formed by the conduction electrons of the metal. This results in a phenomenon known as surface plasmon resonance (SPR). When SPR is induced, the effect is observed as a minimum in the intensity of the light reflected off the metal surface. 

In principle, the sensor constructions rely on five basic sensing schemes transmission, reflection, grazing angle reflection, attenuated total reflection (ATR), and a variant of the ATR effect known as the fibre-evanescent wave sensor (FEWS) (Melting Thomson, 2002). The investigations described in chapters 3 and 4 are based on the use of the ATR technique, focusing on its advantageous properties, esp edally in terms of mechanical robustness. 

IR-transmitting optical fibres are evanescent wave sensors using a mathematical deconvolution technique to extract the absorbances and follow the concentrations of the components as they occur in both laboratory scale and process production. The fibre-optic probe used can be placed at specific locations within the samples or at the surface. The specificity of the technique, the speed of data acquisition and the portability of equipment make this method ideal as a tool to fundamentally probe polymer reactions and processes. Chalcogenide optical fibres are used to direct IR radiation from an FUR spectrometer through an attenuated total reflection (ATR) probe immersed in a reactor and back to the spectrometer. 

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