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Fig. 19 Coumarin based cyanide chemodosimeter; 50 is nonfluorescent, 51 is highly fluorescent
Fig. 20 (a) Fluoride sensing with coumarin leuko dye 52 and (b) time-dependent spectroscopic
response of the reaction; TIPS
triisopropylsilyl group. (Reprinted in part with permission from
[
143
]. Copyright 2003 Wiley-VCH)
¼
other relevant small anions (F
, AcO
, ClO
4
,H
2
PO
4
,Br
,Cl
,I
,NO
3
and
N
3
) and was positively tested for its applicability in vivo [
142
].
The sensing of fluoride with a reaction-based indicator can be based on its
unique reactivity with silicon. As shown in Fig.
20
, the O-Si bond cleavage with
fluoride can be used to produce the coumarin dye 53. For this system, a 100-fold
sensitivity increase was seen after incorporation of the reaction scheme into a
conjugated polymer [
143
].
Regarding neutral small-molecule analytes, reactive oxygen species (ROS) are a
highly topical group. As the term ROS implies, these species should be particularly
well-suited for the development of reaction-based protocols. However, this advan-
tage is at the same time a disadvantage when the aim is the determination of a single
species and not of “ROS” as a sum parameter. For instance, a well-established ROS
probe like 54 responds only in a rather unselective way to oxidation especially by
oxygen-based radicals (Fig.
21
)[
144
]. A more sophisticated approach toward H
2
O
2
sensing was realized with 56. It invokes a hydroboration/oxidation approach and is
based predominantly on the hydrolytic abilities of hydrogen peroxide rather than on
its oxidation potential. Whereas the latter can be easily reached by other ROS, the
basicity and nucleophilicity of the hydrogen peroxide anion is comparatively
unique. Therefore, chemodosimeter 56 reaches a
500-fold selectivity over other
anionic ROS and at least a 3-fold selectivity over radical ROS in water at pH 7 and
was also shown to be applicable in living cells [
145
].
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