Fiber Optical Chemical Sensor applications

Optical fibers are produced in many different configurations, formats, and sizes. For some fiber-optic chemical sensor applications, single optical fibers with diameters ranging from 50 to 500 p.m are employed. For... 

Fig. 5 A modified optical fiber for chemical sensor applications...

For the evaluation of the SIM technique in chemical sensors application, an experimental set-up was developed as shown in Fig. 31. A fiber-optic chemical sensor was prepared, using polyaniline as the modified cladding for a short MM sensing fiber. The spin-casting method was used for coating a thin layer of polyaniline material on the fiber core surface. Then, the modified fiber was tested for the detection of HCl vapor and NH3 gas. The sensor was tested by both the total intensity modulation and the SIM techniques. 

This section attempts to present a broad review of this technique in the light of recent research on fiber-optic chemical sensors (FOCS). A discussion on the advantages and performance of pH optodes will be broached by considering the various applications planned and the resulting pH measurements, including titration and ionic strength. Sensors for low molecular weight electrolytes, particularly optodes for anions and cations in solution, are also considered. 

Fiber optic chemical sensors and biosensors offer important advantages for in situ monitoring applications because of the optical nature of the detection signal. Recent advances in nanotechnology leading to the development of optical fibers with submicron-sized dimensions have opened up new horizons for intracellular measurements. 

Des, Preparation, and Applications of Fiber-Optic Chemical Sensors for Continuons Monitoring... 

Fiber-Optic Chemical Sensors Lasers, Nuclear Pumped Lasers, Solid-State Lasers, Ultrafast Pulse TLchnology Nonlinear Optical Processes Optical Amplifiers Optical Fibers, Fabrication AND Applications Optical Fiber ItcHNiQUES for Medical Applications Optical Waveguides and Waveguide Devices TfeLECOMMUNiCATioNS... 

Successful development of fiber optic chemical sensors requires co-operation of many specialists in various fields of science. Scientists in analytical chemistry, polymer science, material science, optoelectronics and electronics etc. can be involved in this multidisciplinary task. In dependence on the application of the sensor biologists, medical doctors or environmentalists can be incorporated to the working group. Although, the contribution of all specialists cannot be classified by the importance, analytical chemistry and material science seem to be the key to the success. 

Optical fibers and the instrumentation used in fiberoptic chemical sensors are described in Section II. We describe how different optical phenomena, generated by different sensing mechanisms, can be applied to optical fibers to measure analytical signals. These sensing mechanisms are described in Section HI. Section IV reviews several fiber-optic chemical sensor analytical applications in the clinical, industrial, and environmental fields and Section V reviews recent developments in fiber-optic chemical sensors. 

FIGURE 1 Schematic diagram of a fiber-optic chemical sensor system with examples of environmental, clinical, and industrial applications. 

In vivo analytical devices ideally should be capable of monitoring several different physiological parameters simultaneously without interfering with an ongoing medical procedure, such as surgery. The devices should be biocompatible, simple to implement and operate, and highly reliable and safe. Fiber-optic chemical sensors can meet most of these requirements since the optical fibers are small (few hundred micrometers in diameter), flexible, nontoxic, and chemically inert. Optical fibers have already proven to be valuable for in vivo clinical applications such as endoscopic procedures and laser power transmission for surgical applications. 

Multianalyte fiber-optic chemical sensors are in the first stages of research and development. Dne to their importance for many analytical applications, it is expected that research efforts will continue to advance the capabilities of such sensors. 

Fiber-optic chemical sensors offer several advantages over other sensing technologies based on the unique characteristics of optical fibers. The principal advantages include their immunity to harsh environmental conditions (e.g., electromagnetic interference, high temperature, high pH) and their ability to function without any direct electrical connection to the sample. These features have resulted in the development of different flber-optic chemical sensors for analytical applications in the clinical, environmental, and industrial fields. 

The use of fiber-optics in the preparation of the optical sensors allows performing spectroscopy measurements at sites that are inaccessible to conventional spectroscopy and also over large distances. Moreover, the possibility of using evanescent wave spectroscopy and spatially resolved lifetime spectroscopy makes FOCS (fiber optics chemical sensors) a very interesting option for building the sensors. Comprehensive reviews [183,184] on fiber-optic chemical sensors are available, where the most interesting applications of sol-gel coatings for optical sensors are described. 

Design, preparation, and applications of fiber-optic chemical sensors for continuous monitoring. A.C.S. Symposium Series, 403, 253-272. 

The FPI principle can also be used to develop thin-film-coating-based chemical sensors. For example, a thin layer of zeolite film has been coated to a cleaved endface of a single-mode fiber to form a low-finesse FPI sensor for chemical detection. Zeolite presents a group of crystalline aluminosilicate materials with uniform subnanometer or nanometer scale pores. Traditionally, porous zeolite materials have been used as adsorbents, catalysts, and molecular sieves for molecular or ionic separation, electrode modification, and selectivity enhancement for chemical sensors. Recently, it has been revealed that zeolites possess a unique combination of chemical and optical properties. When properly integrated with a photonic device, these unique properties may be fully utilized to develop miniaturized optical chemical sensors with high sensitivity and potentially high selectivity for various in situ monitoring applications. 

Last, but not least, full application of QDs in chemical sensors would require the immobilization of the nanoparticles into appropriate solid supports in order to develop reliable active phases (able to provide, for instance, convenient fiber optic-based sensing applications). Although only a few reports have been published so far regarding the trapping of the QDs in solid matrices, some important steps have already started towards the realization of the potential of these technologies. There is still plenty of room for further development in all those directions. 

In this chapter, an overview on fiber-optic chemical and biosensors is presented focusing on transducers and transduction mechanisms, sensor design, sensor development and processing, and sensor characterization and optimization. A few examples are presented on chemical vapor detection and biosensing applications. At the end of the chapter, the theory and application of the newly developed detection technique, which is called the SIM technique, is presented. 

The modification of the optical fiber involves two major steps, for chemical sensor application [19, 20] (1) removal of the passive cladding (fiber etching) and (2) application of active cladding (fiber coating). The etching and coating processes are explained next. An all-silica MM fiber with core/cladding/jacket dimension of 105/125/250 pm was selected for such application. 

The basic principles and a general survey of chemical sensor applications based on fiber optics, have been adequately given by Seitz (1) and Angel (Z) lt= Is quite evident from the numerous... 

Fiber optic pH sensors have distinct advantages over pH electrodes. They are small, not interfered by electromagnetic flelds and have remote sensing capability. They can be used in extreme environments, such as deep-water analysis, chemical reactors, or wastewater. Moreover, they can be intrinsically referenced due to the dual wavelength measurement capabiUty and do not require a reference electrode [90]. Optical pH sensors also pave the way for imaging applications, whereas pH electrodes only enable punctiform pH measurements. Sensors for pH determination are also of high significance in environmental and marine research because they provide the basis for CO2 sensors. 

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