Polymer optical fibre sensors

The nonlinear optical and dielectric properties of polymers find increasing use in devices, such as cladding and coatings for optical fibres, piezoelectric and optical fibre sensors, frequency doublers, and thin films for integrated optics applications. It is therefore important to understand the dielectric, optical and mechanical response of polymeric materials to optimize their usage. The parameters that are important to evaluate these properties of polymers are their dipole moment polarizability a, hyperpolarizabilities 0... 

PS2 activity measurements were done with an oxygen sensor consisting of a polymer optical fibre (POF) coated with an oxygen-sensitive foil (Presens, Regensburg, Germany) as specified in [Nowaczyk et al., in this book]. 

Philipp, L., Mario, W., Sascha, L. Katerina, K. [2010]. Distributed humidity sensing based on rayleigh scattering in polymer optical fibers. Proceedings of SPIE in Fourth European Workshop on Optical Fibre Sensors, Vol. 7653, SPIE, Porto, Portugal, p>p. 1—4. 

Applications of the fibre optics transmittance or ATR probe are in quality control, reaction monitoring, skin analysis, goods-in checking, analysis at high and low temperature, radioactive or sterile conditions, and hazardous environments. Applications of the reflectance probe are for turbid liquids, powders, surface coatings, textiles, etc. By using an on-line remote spectrophotometer, real-time information is gathered about a chemical process stream (liquids, films, polymer melts, etc.), as often as necessary and without the need to collect samples. This determines more reliable process control. Remote spectroscopy costs less to maintain and operate than traditional techniques. Fernando et al. [48] have compared different types of optical fibre sensors to monitor the cure of an epoxy resin system. 

Successful development of fibre optic chemical sensors requires the cooperation 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. Depending on the application of the sensor biologists, medical doctors or environmentalists can also 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. 

Polymer materials are frequently used matrices for the indicator chemistry in optical sensors. This is necessary for several reasons first, the indicator has to be immobilized to an optical waveguide or an optical fibre which is then brought into contact with the analyte solution. If one would pour an aqueous solution of the indicator dye directly into the sample solution, e.g. into a bioreactor, then the whole sample solution would be contaminated. 

The first intravascular sensor for simultaneous and continuous monitoring of the pH, pC>2, and pCC>2 was developed by CDI-3M Health Care (Tustin CA)14 based on a system designed and tested by Gehrich et al.15. Three optical fibres (core diameter = 125 pm) are encapsulated in a polymer enclosure, along with a thermocouple embedded for temperature monitoring (Figure 3). pH measurement is carried out by means of a fluorophore, hydroxypyrene trisulfonic acid (HTPS), covalently bonded to a matrix of cellulose, attached to the fibre tip. Both the acidic ( eXc=410 nm) and alkaline ( exc=460 nm) excitation bands of the fluorophore are used, since their emission bands are centred on the same wavelength (/-cm 520 nm). The ratio of the fluorescence intensity for the two excitations is measured, to render the sensor relatively insensitive to fluctuations of optical intensity. 

Linear oligonucleotide probes have been immobilized along the length of fibres as well as on the distal end of fibres. Healey et al. [88] described the immobilization of three different oligonucleotide probes in acrylamide polymer matrices at the distal ends of optical fibres. Base pair mismatches could be distinguished on the same sensor after a 20-min hybridization with a detection limit of 0.2 nM [88]. More recently, zeptomole ( 600 molecule) detection limits have been obtained by using etched distal ends of optical fi-... 

Initially, the performance of the PMP sensor was evaluated with a 1/2 metre monochromator equipped with a CCD detector to obtain figures of merit. The sensor was also evaluated using a fibre optic spectrometer from Ocean Optics, Model S2000. The sensor used to determine the limit of detection (LOD) consisted of a 400 mm optical fibre with a tapered end. A 50-75 mm layer of the 3 mole % complex polymer was directly deposited onto the tapered end without vinyl-silanisation. Using 1 mW of 465.8 nm for excitation, 200 pm entrance slits of the... 

Luminescence probes can be made by employing the polymer as a coating for an optical fibre. The polymer coating can be directly applied to the fibre as with the PMP sensor above, it can be bonded to a vinyl-silanised fibre surface or it can be implanted as a fine powder in a sol-gel coating. The fibre sensor can be addressed in a variety of ways [34], of which the simplest is to use a bifurcated fibre. In this configuration the sensor is attached to the common leg and the detector and source are attached to the bifurcated legs. This configuration is illustrated in Fig. 19.12. 

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. 

Kondratowicz B, Narayanaswamy R, Persaud KC (2001) An investigation into the use of electrochromic polymers in optical fibre gas sensors. Sens Actuators B 74 138-144... 

Rohe et al. [157-159] have developed a fibre optic transmission sensor for application of AOTF-NIR spectroscopy to extrusion processes, so that real inline observation is possible. The parameters measured on-line are often not sufficient for adequate description of the polymeric melt. NIR spectroscopy can solve this lack of knowledge by in-line measurements of the melt. The polymer composition of a PE/PP blend during extmsion was determined with high accuracy (deviation <2%) using a polymeric melt analyser on the basis of in-line transmission AOTF-NIR spectroscopy and multivariate data analysis [157],... 

One can, however, envisage new applications other than in the area of display devices. These would include new types of heat and infrared sensors, ferroelectric tapes, plastics, polymers and optical fibres. In particular, the very large number of new dipolar organizations [58-60] that can be realized in such materials could be used to form high density optical and electronic memories. 

Yan H.M., Kraus G., Gauglitz G., Detection of Mixtures of Organic Pollutants in Water by Polymer Film Receptors in Fibre-Optical Sensors Based on the Reflectometric Interference Spectrometry, Anal ChimActa 1995 312 1-8. 

Any (bio)chemical reaction is accompanied by energy conversion, most often in the form of heat production, the amount of heat produced being proportional to that of substance converted. Therefore, heat is a highly nonspecific expression of a (bio)chemical reaction but can be used as indicative for a given substance when this is selectively converted (e.g. by effect of a catalyst, particularly an enzyme). This section discusses three types of sensors based on the use of as many types of devices for measurement of the heat involved in a biochemical reaction, namely fibre optics, polymer films and thermistors. 

These two methods can be adapted for use in the commercially attractive area of polymer bound sensors. These offer, especially when coupled with fibre optics, a safe way of examining flammable solvents for their composition and levels of liquid impurities. 

Hardware sensors for the on-line monitoring of polymerization such as in batch reactors have been reviewed (Kammona et al. 1999). In Section 3.4 the use of ruggedized conversion sensors for fibre-optic near-infrared (NIR) spectroscopy during extrusion was described. In many ways, the requirements are simpler than for control of a batch reaction (as in a polymer-synthesis autoclave) since... 

---