Optimization of the Coupling of Target Recognition and Signal Generation - Advanced Fluorescence Reporters in Chemistry and Biology - page 82

Fig. 32 Effect of analyte coordination in (a) a traditional molecular chemosensor system,
(b) receptors wired in series in a conjugated polymer, (c) chemosensors grafted onto the surface
of a nanoparticle, and (d) a fluorescent dendrimer. The curved arrows indicate the active
processes, e.g., quenching

Contrary to what happens with conventional fluorescent chemosensors, for which
the recognition of the target by the receptor unit affects only the fluorescence
properties of a single covalently coupled fluorescent moiety, for the locally con-
centrated systems, a single binding event can modulate the fluorescence behavior of
more than one fluorescent unit in the immediate neighborhood. The different types
of systems realized along this strategy are illustrated in Fig. 32 . The net effect is the
transduction of a single binding event by an amplified response of several fluoro-
phores. These collective effects will be discussed in the next chapter [ 23 ]. In the
following, we will discuss the cases of conjugated fluorescent polymers, fluores-
cently doped dendrimers, and NPs.

4.4.1 In Conjugated Polymers

The dominant attribute that has driven interest in fluorescent conjugated polymers
(CPs) sensory materials is their ability to produce signal gain in response to
interactions with analytes. The increased sensitivity (amplification) is derived
from the ability of a conjugated polymer to serve as a highly efficient transport
medium of electronic excitation. Analyte specificity in CP-based sensors results
from the covalent or physical integration of receptors, imprinting, and/or the CP's
overall electrostatic and chemical characteristics. The observed amplification is a