Optimization of the Coupling of Target Recognition and Signal Generation - Advanced Fluorescence Reporters in Chemistry and Biology - page 95

into numerous directions. At the heart of many of these attempts is the question of
how molecular systems can be better designed to show ever more selective and
sensitive responses to target analytes. One of the key issues is to couple the
recognition event with strong signal modulation, at best in an amplifying manner.
In the present contribution, we have illustrated the main concepts that have so far
been developed for fluorescent reporters and reporting systems for ionic and small-
molecule inorganic and organic species.
Naturally, such an overview can be anything but complete. In addition, it can
only highlight the basis of the single concepts and discuss selected examples, but
cannot raise too many details, evaluate the strategies in a comprehensive manner, or
even give upfront recipes for the reader who is interested in the detection of a
particular analyte. The attentive reader has noticed that we mentioned actual
fluorescence enhancement/amplification factors only scarcely and might ask, why?
The answer lies in the details. As anyone who sheds a glimpse into supramolecular
chemistry knows well, noncovalent interactions depend tremendously on the sol-
vent and/or buffer/ionic strength used in the study, the counterions (if applicable),
and other experimental conditions. However, different researchers or different labs
tend to use (if only slightly) different conditions. This makes a serious comparison
of the data published on the many reported systems impossible without being
unjust. Moreover, space also forbade the discussion of solvent or counterion effects
in more detail; the reader has to revert to original literature. As a general advice
it must be said that the majority of examples published until today in the fields
presented in Sects. 2 and 3 still need a certain (sometimes still high) degree of
organic (co-)solvent for operation. Although many of these approaches are intel-
lectually very rewarding, it is exactly this drawback for actual applications which
has stimulated much of the research in alternative directions that we have combined
in Sect. 4 . It is still a long and laborious road from the first idea or analytical
question to a chemosensor that is applicable under realistic conditions.
So, what's next? Of course, research on all fronts will advance, with the
approaches in Sect. 4 receiving perhaps the highest attention. The rapid develop-
ment of nanoscopic and nanostructured materials has specially opened the path to
sophisticated sensing ensembles Sousa and V ¨ gtle would not even have dreamed
about [ 228 , 229 ]. However, for many applications, small molecules as reporters are
indispensible, simply because of their size and the possibilities of interaction at the
molecular level so that their future exploration is also essential. Finally, since
technology will advance, new instrumental techniques and possibilities will appear
and automatically fuel research on powerful fluorescent reporters.
6 Further Reading
Besides [ 1 - 27 , 176 ] and the two seminal series on all aspects of fluorescence
spectroscopy and fluorophores [ 230 , 231 ], several monographs have appeared in
the field of fluorescent reporter/functional fluorophore design and their application