Chemical sensors optically-coupled

One example are fibre-optic chemical sensor systems for volatile organic pollutants in water49 53. These sensors are based on coupling the IR radiation... 

This chapter provides an overview of the basic principles and designs of such sensors. A chemical sensor to detect trace explosives and a broadband fiber optic electric-field sensor are presented as practical examples. The polymers used for the trace explosive sensor are unpoled and have chromophores randomly orientated in the polymer hosts. The electric field sensor uses a poled polymer with chromophores preferentially aligned through electrical poling, and the microring resonator is directly coupled to the core of optical fiber. 

Fluorescent pH indicators offer much better sensitivity than the classical dyes such as phenolphthalein, thymol blue, etc., based on color change. They are thus widely used in analytical chemistry, bioanalytical chemistry, cellular biology (for measuring intracellular pH), medicine (for monitoring pH and pCC>2 in blood pCC>2 is determined via the bicarbonate couple). Fluorescence microscopy can provide spatial information on pH. Moreover, remote sensing of pH is possible by means of fiber optic chemical sensors. 

The combination of selectivity of biochemical origin with the high intrinsic selectivity of optical spectroscopy makes the optical sensors potentially the most selective of all types of chemical sensors. It is not surprising, because most bioassays use optical detection. Moreover, the coupling requirements between the primary interactions in the selective layer and the transducer part of the sensor are relatively simple. The molecule that provides the signal (absorber) merely has to be present in the optical path in order to be counted. 

Chemical sensors utilize the immunological recognition principle by coupling with optical, electrochemical, or other transducer (signal transfer) described e.g. by Eggins (1996) and Rogers et al. (1998). A tendency to miniaturized formats ( chips ) as part of the nanotechnology can be observed. 

Hale Z M and Payne F P 1994 Fluorescent sensors based on tapered single-mode optical fibres Sensors Actuators 17 233 0 Luo S and Walt D R 1989 Avidin-biotin coupling as a general method for preparing enzyme-based fiber-optic sensors Anal. Chem. 61 1069-72 Li L and Walt D R 1995 Dual-analyte fiber-optic sensor for the simultaneous and continuous measurement of glucose and oxygen Anal. Chem. 67 3746-52 Tan W, Shi Z-Y, Smith S, Bimbaum D and Kopelman R 1992 Submicrometer intracellular chemical optical fiber sensors Science 258 778-81 Tan W, Shi Z-Y and Kopelman R 1992 Development of submicron chemical fiber optic sensors Anal. Chem. 64 2985-90... 

Nevertheless, a steady rapid development of immunotests can be observed, especially in the field of environmental monitoring [l]-[3], where the question of costs has become so important that the establishment of an immunotest can be worthwhile in spite of all the facts mentioned above. In the development of chemical sensors, efforts are also being made to utilize the biochemical recognition principle by coupling with optical, electrochemical, or other transducer (signal transfer) [4] - [6]. However, the slower kinetics involved in molecular biological processes require stricter maintenance of the experimental protocol, e.g., the time of reaction between the antibody and the tracer molecule or analyte (hapten) should be set up in an exactly reproducible manner by means of flow-injection analysis 7],... 

Mayr T, Abel T, Enko B, Borisov S, Konrad C, Kostler S, Lamprecht B, Sax S, List EJW, Klimant I (2009) A planar waveguide optical sensor employing simple light coupling. Analyst 134 1544-1547 McAlpine MC, Ahmad H, Wang D, Heath JR (2007) Highly ordered nanowire arrays on plastic substrates for ultrasensitive flexible chemical sensors. Nat Mater 6 379-384... 

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