Fluorescent optical chemical sensors sensitivities

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). 

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. 

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. 

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. 

Wohltjen H, Barger WR, Snow AW, Jarvis NL (1985) A vapor-sensitive chemiresistor fabricated with planar microelectrodes and a Langmuir-Blodgett organic semiconductor film. IEEE Trans Electron Dev ED-32 1170-1174 Wolfbeis OS (1991) Fiber optic chemical sensors and biosensors, vol 1. CRC, Boca Raton, FL Wolfbeis OS (1992) Fiber optic chemical sensors and biosensors, vol 2. CRC, Boca Raton, FL Wolfbeis OS (2005) Materials for fluorescence-based optical chemical sensors. J Mater Chem 15 2657-2669 Wollenstein J, Plaza JA, Can6 C, Min Y, Bottner H, Tuller HE (2003) A novel single chip thin film metal oxide array. Sens Actuators B 93 350-355... 

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... 

Fluorescent chemical sensors occupy nowadays a prominent place among the optical devices due to its superb sensitivity (just a single photon sometimes suffices for quantifying luminescence compared to detecting the intensity difference between two beams of light in absorption techniques), combined with the required selectivity that photo- or chemi-luminescence impart to the electronic excitation. This is due to the fact that the excitation and emission wavelengths can be selected from those of the absorption and luminescence bands of the luminophore molecule in addition, the emission kinetics and anisotropy features of the latter add specificity to luminescent measurements8 10. 

Keywords Absorption ARROW waveguide Biosensor Chemical sensor Confinement Dielectrics Evanescent field Fiber optics Fluorescence Hollow core Liquid-core Loss Optical mode Photonic crystal Refractive index Resolution Scattering Sensitivity Total internal reflection Waveguide... 

Fluorescence and chemiluminescence sensors are considered the most sensitive in the class of optical sensors. They have a higher selectivity because the chemiluminescent and fluorescent reactions take place in certain medium conditions, and only a limited group of ions and molecules can be involved. When the selectivity of this type of sensor is not sufficient, the quality of analysis can be improved by using a biochemical reaction such as an enzymatic reaction (chemiluminescence- or fluorescence-based biosensors) or an immunoreaction (chemiluminescence- or fluorescence-based immunosensors). By using these types of optical sensors the chemical analysis becomes most sensitive and selective.265... 

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