11 Fluorescent Chemosensors
387
and excited states can be estimated (Lippert-Mataga equation) (Mataga et al. 1956,
2005; Lippert 1957). If the difference is large, then the dye has strong ICT characteristics and therefore exhibits large Stokes shift, broadened fluorescence, and strong
fluorescence solvatochromism.
E T (30) is a solvent polarity parameter experimentally obtained using Reichart’s
dye as a reference. Specifically, the slope of the fluorescence peak wavenumber
versus E T (30) plot of the solvatochromic dye of interest in given solvents directly
shows dye sensitivity.
Another
class
of
environment-sensitive
dyes
is
typified
by
9-(dicyanovinyl)julolidine (DCVJ) (Klymchenko 2017; Loutfy 2007; Kung
and Reed 1986), which varies its fluorescence intensity in response to the
surrounding viscosity. The sensitivity of such dyes is generally evaluated by using
Förster-Hoffmann equation (Loutfy 2007; Kung and Reed 1986).
In many cases, the abovementioned dyes change in their fluorescence lifetime as
well as fluorescence intensity/color. These properties are also useful for fluorescence
lifetime imaging (FLIM), and therefore their evaluation may expand the utility of
the dyes (vide infra, see Sect. 11.4.8).
11.3.6 Other Considerations
The hydrophilicity/hydrophobicity, cell permeability, and cell toxicity of the newly
developed fluorescent chemosensors may be significant factors in their practical use.
Unfortunately, these considerations are beyond the focus of this chapter due to text
length limit.
11.4 Operation Principles of Fluorescent Chemosensors
As mentioned in Sect. 11.2, fluorescent chemosensors generally capture the analyte
at first and then change in their fluorescence intensity, color, or lifetime through
certain signal transduction mechanisms. Such changes in fluorescence properties
could be observed by a spectrofluorometer, fluorescence microscope, etc. to allow
the detection, quantitation, monitoring, and visualization of the analyte and related
phenomena. On the other hand, it should be kept in mind again that fluorescent
chemosensors that selectively bind to the analyte without changing their fluorescence
properties are also useful makers to visualize the object of interest.
In this chapter, we present representative operation principles by which fluorescent chemosensors change their fluorescence properties, along with the related
photophysical mechanism. It should be noted that multiple principles can function
simultaneously in a single fluorescent chemosensor. In addition, as mentioned in
Sect. 11.1, the binding site itself in fluorescent chemosensors does not have to
directly induce change in the fluorescence signal. That is, even when the binding
387
and excited states can be estimated (Lippert-Mataga equation) (Mataga et al. 1956,
2005; Lippert 1957). If the difference is large, then the dye has strong ICT characteristics and therefore exhibits large Stokes shift, broadened fluorescence, and strong
fluorescence solvatochromism.
E T (30) is a solvent polarity parameter experimentally obtained using Reichart’s
dye as a reference. Specifically, the slope of the fluorescence peak wavenumber
versus E T (30) plot of the solvatochromic dye of interest in given solvents directly
shows dye sensitivity.
Another
class
of
environment-sensitive
dyes
is
typified
by
9-(dicyanovinyl)julolidine (DCVJ) (Klymchenko 2017; Loutfy 2007; Kung
and Reed 1986), which varies its fluorescence intensity in response to the
surrounding viscosity. The sensitivity of such dyes is generally evaluated by using
Förster-Hoffmann equation (Loutfy 2007; Kung and Reed 1986).
In many cases, the abovementioned dyes change in their fluorescence lifetime as
well as fluorescence intensity/color. These properties are also useful for fluorescence
lifetime imaging (FLIM), and therefore their evaluation may expand the utility of
the dyes (vide infra, see Sect. 11.4.8).
11.3.6 Other Considerations
The hydrophilicity/hydrophobicity, cell permeability, and cell toxicity of the newly
developed fluorescent chemosensors may be significant factors in their practical use.
Unfortunately, these considerations are beyond the focus of this chapter due to text
length limit.
11.4 Operation Principles of Fluorescent Chemosensors
As mentioned in Sect. 11.2, fluorescent chemosensors generally capture the analyte
at first and then change in their fluorescence intensity, color, or lifetime through
certain signal transduction mechanisms. Such changes in fluorescence properties
could be observed by a spectrofluorometer, fluorescence microscope, etc. to allow
the detection, quantitation, monitoring, and visualization of the analyte and related
phenomena. On the other hand, it should be kept in mind again that fluorescent
chemosensors that selectively bind to the analyte without changing their fluorescence
properties are also useful makers to visualize the object of interest.
In this chapter, we present representative operation principles by which fluorescent chemosensors change their fluorescence properties, along with the related
photophysical mechanism. It should be noted that multiple principles can function
simultaneously in a single fluorescent chemosensor. In addition, as mentioned in
Sect. 11.1, the binding site itself in fluorescent chemosensors does not have to
directly induce change in the fluorescence signal. That is, even when the binding