Fluorescent optical chemical sensors

Fluorescent tical chemical sensors are (tf particular interest due to their inherent sensitivity and sinq>lidty (2). These types of sensors have many other advantages that optical sensors, in general, offer. One of the most attractive features is that they do not require a separate reference sensor, as a p( tiometric chemical sensor does. In addition, th r are not affected by electrical interferraice, sanq)le flow rate, and stir speed which can be serious problems with eledrochemical sensors. Fluorescent optical chemical sensors have been widdy used for quantitative measurements of various analytes in environmental, industrial, clinical, medical, and biological aj lications (2). 

Tubular shapes for blood vessels and nerve regenerations Three-dimensional scaffolds for bone and cartilage regenerations Liquid filtration Gas filtration Molecular filtration Thermal sensor Piezoelectric sensor Biochemical sensor Fluorescence optical chemical sensor Skin cleansing Skin healing... 

Fig. 5 shows the instrumental arrangement of the commercially most successful optical chemical sensor between 1984 and 2000. It is used in about 70% of all critical care operations in the US to monitor pH, pC02 and p02 in the cardiopulmonary bypass operations35. It contains 3 fluorescent spots, each sensitive for one parameter, in contact with blood. Fluorescence intensity is measured at two wavelengths and the signals are then submitted to internal referencing and data processing. 

Munkholm C., Walt D.R., Milanovich F.P., Klainer S.M., Polymer modification of fiber optic chemical sensors as a method of enhancing fluorescence signal for pEl measurement, Analytical Chemistry 1986 58 1427-1430. 

Wolfbeis OS (2005) Materials for fluorescence-based optical chemical sensors. J Mater Chem 15 2657-2669... 

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. 

From a general point of view, a chemical sensor is a device capable of continuously monitoring the concentration of an analyte. The two main classes are electrochemical sensors and optical chemical sensors. The latter are based on the measurement of changes in an optical quantity refractive index, light scattering, reflectance, absorbance, fluorescence, chemiluminescence, etc. For remote sensing, an optical fiber is used, and the optical sensor is then called an optode because of... 

It is desirable to have means to measure organohalides such as carbon tetrachloride in situ in water and other environmental media. One approach to doing this has been demonstrated by the in situ analysis of chloroform-contaminated well water using remote fiber fluorimetry (RFF) and fiber optic chemical sensors (FOGS) (Milanovich 1986). With this approach, fluorescence of basic pyridine in the presence of an organohalide (Fujiwara reaction) is measured from a chemical sensor immersed in the water at the end of an optical fiber. Carbon tetrachloride undergoes a Fujiwara reaction, so its determination might be amenable to this approach. 

Orellana G (2005) Fluorescence-based sensors. In Martellucci S, Baldini F (eds) Optical chemical sensors. Springer-Kluwer, New York (in press)... 

Wolfbeis, O. S. Materials for Fluorescence-Based Optical Chemical Sensors. J. Mater. Chem. 2005, 15, 2657-2669... 

Fiber-optic chemical sensors for substances such as protons, asygea, and carbon di< dde have been developed. These sensors respond to specific substances in accordance with the fluorescent changes of fluorescent probes. An optical fiber-optic for pH can be couided to enzyme sensors when the enzymes cause a change in pH, which results in a change in fluorescent property of the probe compounds. These optical sensors are named Optrodes, and were extensively reviewed by Seitz (1). 

A pH fiber-optic chemical sensor based on energy transfer has been prepared successfully. This sensor utilizes a polymeric bichromophore and employs a fluorescent donor, eosin, and a non-fluorescent pH sensitive acceptor, phenol red. As pH increases, phenol red s absorption increases in the spectral region that overlaps with the emission spectrum of eosin (Fig.7). Since the extent of energy transfer is proportional to the spectral overlap integral, the efficiency of energy transfa" increases as the pH increases and is detected as a decrease in eo s fluorescence. 

Major Applications pH Sensors, optical chemical sensors, biochemical sensors, biosensors," fluorescent pH detector system, measuring fluorescence lifetime in cells, determining concentration of a laminar sample stream, fluorescent reporter beads for fluid analysis, measuring ch ical analytes, intracellular pH in human sperms, " multidrug resistance," recording intramitochon-drial pH, fluorescent probes ... 

Wolfbeis OS (1991) Fiber optic chemical sensors and biosensors, vol 1. CRC Press, Boca Raton, FL Wolfbeis OS (ed) (1992) Fiber optic chemical sensors and biosensors, vol 2. CRC Press, Boca Raton, FL Wolfbeis OS (2005) Materials for fluorescence-based optical chemical sensors. J Mater Chem 15 2657-2669 Wolfbeis OS, Posch HE (1986) Fiber-optic fluorescing sensor for ammonia. Anal Chim Acta 185 321-327 Wolfbeis OS, Weis LJ, Leiner MJP, Ziegler WE (1988) Fiber-optic fluorosensor for oxygen and carbon dioxide. Anal Chem 60 2028-2030... 

With the objective of preparing fiber optic chemical sensors for pH measiu ements, Millar et al. have recently synthesized a polythiophene poly(27) derivatized by a pH-sensitive fluorescein unit [343]. As expected, the fluorescence properties of the polymer... 

Optical fibers are commonly used for remote monitoring of fluorescent analytes. Fiber-optic chemical sensors can provide both qualitative and quantitative information about the analyte under consideration. Since each analyte has different fluorescent properties, selective measurements can be performed by choosing the correct excitation and emission wavelengths. The fluorescence bands are usually quite broad and the bands for a class of compounds overlap, so it may be difficult to distinguish among them. Fluorescence lifetime measurements are sometimes... 

C. Ion sensing. Several different schemes can be applied to fiber-optic chemical sensors for detecting ions other than hydrogen. One approach is to design a system, similar to pH fiber-optic chemical sensors, in which a dye that selectively binds a metal ion of interest is immobilized in an ion-permeable polymer such as cellulose or a hydrogel at the tip of an optical fiber. The reaction between the dye and the ion changes the absorbance or fluorescence of such dyes. Absorbance or fluorescence intensity changes are measured as a function of ion concentration, but this... 

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