Detectors fiber optic chemical sensors

The basic design of a fiber-optic chemical sensor system is shown in Fig. 1. The fiber-optic chemical sensor s main components are (a) a light source, (b) optical fibers fo both transmit the light and act as the substrate for (c) the sensing material, and (d) a detector to measure the output light signal. Usually computers or microprocessors control the fiber-optic chemical sensor instrumentation and are employed to analyze the output signals. 

In most fiber-optic chemical sensor systems, the light transmitted from the sensing element (output light) is measured by using photon detection devices, which absorb photons and convert them into electrical signals. Several photon detectors are available. The simplest and cheapest detector is the silicon photodiode. In this solid-state device, photon detection is based on p-n semiconductor... 

Typical fiber-optic chemical sensors for in vivo monitoring are constructed from optical fibers that are connected to an external compact unit containing the light source and the detector, as shown in Fig. 18. The optical fiber s distal end is inserted into the patient through a catheter. 

The combination of chemical and biological sensors with flow injection has been demonstrated. Both more-traditional-type sensors such as pH electrodes and newer sensors such as fiber optics and surface acoustic wave detectors have been incorporated into FIA systems with success. An advantage that FIA brings to the sensor field is the possibility of turning a moderately selective sensor into a selective sensor by incorporating into the FIA system some type of selectivity enhancement technique such as gas diffusion, dialysis, and reactors. Finally the FIA systems permit renewable systems since sensor surfaces and reaction cells can be washed, surface regenerated, and reagents replenished on demand. 

A variety of transducer configurations that has been employed in photometric sensor devices fall into two sensor types extrinsic sensors and intrinsic sensors. While in the former sensor type the optical fiber merely acts as a light guide, conveying the optical information between the optical source and the chemical transducer and between the chemical transducer and the detector, in the latter sensor type the optical fiber, probably in some modified form, would become a part of the transducer. 

Optical (fiber) chemical sensors [1] are capable of measuring a single species in an untreated sample by simply bringing into contact sample and sensor Separation steps or addition of chemical reagents are not required This is the preferred method in case of samples where the matrix does not vary to a large extent, e g blood However, optodes also represent useful detectors for use in chromatography, flow injection analysis... 

There is considerable technological interest in IR transmissive materials with applications ranging from IR detectors and imaging systems, to fiber optics for telecommunications, chemical sensors, and for piping radiation from large CO2 or Er YAG lasers to the point where it is needed for surgery or industrial cutting operations. 

Here A and B are non-luminescence molecules. The C is the excited state of the product C. Often these reactions involve oxidation reactions and the presence of a catalyst. Both chemical and biochemical reactions could generate the photon. The intensity of the photons are collected through optical fibers and measured with a photon detector. The most successful chemiluminescence sensor for the detection of the hydrogen peroxide [13] is based on luminol using ferricyanide as catalyst... 

OFDs can be divided into two subclasses (1) optical fiber chemical detectors (OFCD) which detect the presence of chemical species in samples, and (2) optical fiber biomolecular detectors (OFBD) which detect biomolecules in samples. Each subclass can be divided further into probes and sensors, and bioprobes and biosensors, respectively. As a result of the rapid expansion of optical research, these terms have not been clearly defined and to date, the terms probe and sensof have been used synonymously in the literature. As the number of publications increases, the terminology should be clarified. Although both probes and sensors serve to detect chemicals in samples, they are not identical. The same situation exists with bioprobes and biosensors. Simply, probes and bioprobes are irreversible to the analyte s presence, whereas sensors and biosensors monitor compounds reversibly and continuously. 

Fiberoptic sensors can be used to measure PAHs in situ A xenon lamp is a common excitation source when connected to optical fiber to excite a sample remotely and induce fluorescence. The fluorescence light emitted is collected by another optical fiber and transmitted to a photomultiplier detector. Sensors are chemically modified to enhance selectivity and sensitivity. (3-cyclodextrins and immunochemical reagents on optical fiber probes can selectively determine individual PAHs but with some crossreactivity. Fluorescence probes such as perylene can be imbedded in polymers affixed to the end of the probe. 

The reagent phases in chemical transducer-based sensors are normally fabricated by using physical or chemical methods, as described earlier in this article, and these are interfaced appropriately with optical fibers in order to produce an optimal sensor design with respect to a particular type of application. In these sensors aside from the chemical transduction process that recognizes the analyte interaction, the optical signals transmitted to the detector also need to be transduced further into a measurable electrical signal that can be displayed, usually, by a meter. 

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