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Y. Niko and S. Watanabe
11.1 Definition of “Fluorescent Chemosensors”
“Fluorescent chemosensors” and “fluorescent probes” are often used as interchangeable terms, although some readers may associate different types of observation object,
available instrument, and sensing mechanism with each term. For instance, some
people regard fluorescent chemosensors to be molecules for sensing ions or other
chemical species using spectroscopic methods, whereas fluorescent probes are tools
for visualizing inter/intracellular biomolecules, cell organelles, or tissues by means
of microscopy. A similar terminological confusion comes from the function of fluorescent molecules. For some people, fluorescent chemosensors should be able to vary
their fluorescent properties when the sensor captures the analyte. While this might be
the general definition of fluorescent chemosensors (Rice et al. 2002), the sensors may
be called “fluorescent chemodosimeters” instead when their binding to the analyte
is irreversible. On the other hand, some fluorescent molecules simply bind to the
analyte without any specific change in their fluorescence properties. While these
molecules certainly have their uses, they tend to be excluded from the category of
fluorescent chemosensors and termed instead as fluorescent probes, markers, and so
on.
To avoid the terminological confusion, here the authors would like to include
what may be known as fluorescent chemodosimeters, fluorescent probes, etc. in the
discussion of fluorescent chemosensors. That is, all fluorescent molecules capable of
quantitative/qualitative analysis, monitoring, or visualization of their target objects
will be regarded as fluorescent chemosensors in this chapter.
11.2 Molecular Structure of Fluorescent Chemosensors
11.2.1 Components
Basically, fluorescent chemosensor consists of a fluorophore as a signal indicator
and a binding site to capture the analyte of interest. When the fluorescent function
of the sensor is activated by host–guest interaction (vide infra, see Sect. 11.4.1), its
binding site may be called a “receptor”. Moreover, if the binding is selective for the
receptor in proteins, the binding molecule will be called a “ligand”. To avoid this
terminological complexity, the phrases “fluorophore” and “binding site” are used as
much as possible in this chapter.
Generally, fluorophores are selected from functional dyes as described in Chaps. 1,
2, 3, 4, 5 and 6. On the other hand, there are many different types of the binding site.
For instance, the receptors (chelators) in host–guest chemistry, typified by the crown
ether family (Wu et al. 2017; Rice et al. 2002), ligands for receptors in peptides
(Kubota and Hamachi 2015), aptamers (Famulok et al. 2007), antibodies (Urano
et al. 2009), and others (Wu et al. 2015; Sapsford et al. 2013; Zhu et al. 2016),
have been intensively used as binding sites in fluorescent chemosensors. However, it
Y. Niko and S. Watanabe
11.1 Definition of “Fluorescent Chemosensors”
“Fluorescent chemosensors” and “fluorescent probes” are often used as interchangeable terms, although some readers may associate different types of observation object,
available instrument, and sensing mechanism with each term. For instance, some
people regard fluorescent chemosensors to be molecules for sensing ions or other
chemical species using spectroscopic methods, whereas fluorescent probes are tools
for visualizing inter/intracellular biomolecules, cell organelles, or tissues by means
of microscopy. A similar terminological confusion comes from the function of fluorescent molecules. For some people, fluorescent chemosensors should be able to vary
their fluorescent properties when the sensor captures the analyte. While this might be
the general definition of fluorescent chemosensors (Rice et al. 2002), the sensors may
be called “fluorescent chemodosimeters” instead when their binding to the analyte
is irreversible. On the other hand, some fluorescent molecules simply bind to the
analyte without any specific change in their fluorescence properties. While these
molecules certainly have their uses, they tend to be excluded from the category of
fluorescent chemosensors and termed instead as fluorescent probes, markers, and so
on.
To avoid the terminological confusion, here the authors would like to include
what may be known as fluorescent chemodosimeters, fluorescent probes, etc. in the
discussion of fluorescent chemosensors. That is, all fluorescent molecules capable of
quantitative/qualitative analysis, monitoring, or visualization of their target objects
will be regarded as fluorescent chemosensors in this chapter.
11.2 Molecular Structure of Fluorescent Chemosensors
11.2.1 Components
Basically, fluorescent chemosensor consists of a fluorophore as a signal indicator
and a binding site to capture the analyte of interest. When the fluorescent function
of the sensor is activated by host–guest interaction (vide infra, see Sect. 11.4.1), its
binding site may be called a “receptor”. Moreover, if the binding is selective for the
receptor in proteins, the binding molecule will be called a “ligand”. To avoid this
terminological complexity, the phrases “fluorophore” and “binding site” are used as
much as possible in this chapter.
Generally, fluorophores are selected from functional dyes as described in Chaps. 1,
2, 3, 4, 5 and 6. On the other hand, there are many different types of the binding site.
For instance, the receptors (chelators) in host–guest chemistry, typified by the crown
ether family (Wu et al. 2017; Rice et al. 2002), ligands for receptors in peptides
(Kubota and Hamachi 2015), aptamers (Famulok et al. 2007), antibodies (Urano
et al. 2009), and others (Wu et al. 2015; Sapsford et al. 2013; Zhu et al. 2016),
have been intensively used as binding sites in fluorescent chemosensors. However, it