Fiber-optic-based fluorescence sensing

With respect to fiber-optic-based fluorescence sensing, most of the past approaches have employed either excitation or emission wavelength selectivity (10,11). The other selectivity parameters fluorescence lifetime, steady-state polarization, and rotational diffusion rates have received little if any attention. The acquisition of fluorescence lifetime information via optical fibers has been demonstrated previously (12) however, the time resolution and ability to resolve multiexponential decays of fluorescence were neither demonstrated nor possible with this earlier instrument. Recently, our own group (13,1 ) has developed and described the first fiber-optic-based fluorescence lifetime instrumentation capable of unequivocally determining single, double, and/or triple exponential decays of fluorescence in remotely-located samples. 

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. 

Figure 11.15. Schematics of the optical arrangement and temperature probes for the Cr+ fluorescence lifetime-based fiber optic thermometers. F = short-pass optical filter Fa = bandpass or long-pass optical filter LD = laser diode LED = light emitting diode S = the fluorescence material used as sensing element vm = signal to modulate the output intensity of the excitation light source v/= the detected fluorescence response from the sensing element.

Z. Zhang, K. T. V. Grattan, A. W. Palmer, R. Summers, R. Summan and S. Hughes, Cr LiSAF fluorescence lifetime based fiber optic thermometer and its application in clinical rf heat treatment, in Advances in Fluorescence Sensing Technology (J. R. Lakowicz and R. B. Thompson, eds.), Proc. SPIE 1885, 300-305(1993). 

J. R. Lakowicz, H. Szmacinski and K. W. Berndt, Fluorescence lifetime-based sensing of blood gases and cations, in Fiber Optic Medical and Fluorescent Sensors and Applications (J. R. Lakowicz, ed.), Proc. SPIE. 1648, 150-163 (1992). 

In particular optical sensing systems belong to this group, which are described in detail in Chapter 27. For example, fluorescent reporter groups are incorporated into the MIP, the properties of which are altered upon analyte binding [14-16]. A very sensitive sensor for a hydrolysis product of the chemical warfare agent Soman has been described based on a polymer-coated fiber optic probe and a luminescent... 

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