Page 358 - Organic Electronics in Sensors and Biotechnology

Luminescent Conjugated Polymers for Staining and Characterization of Amyloid Deposits 335

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Chromophore/Quencher-labeled
Cationic Helical zwitter-ionic Single-stranded
polyfluorene Single-stranded PNA-probe polythiophene DNA-probe (ssDNA)
(peptide nucleic acid)
Hybridization
Polymer/ssDNA complex
Rod-shaped and aggregated
polymer chains
Energy transfer
superquenching Hybridization

Polymer/dsDNA Polymer/dsDNA complex
complex Non-planar and separated polymer chains
FIGURE 9.3 Schematic drawing of the detection of DNA hybridization by luminescent
conjugated polymers. The technique using FRET or superquenching from the polymer
chain is shown at left, and the technique using the geometric changes of the
polymer chains to detect the hybridization event is shown at right.

However, in all cases, the detection and recognition events are due to
the covalently attached side chains, and these chemical modifications
require advanced synthesis and extensive purification of numerous
monomeric and polymeric derivatives.Also the first-generation sen-
sors were utilizing optical absorption as the source for detection, and
the sensitivity of these sensors was much lower compared with other
sensing systems for biological processes.
To avoid covalent attachment of the receptor to the polymer side
chain and to increase the sensitivity of the biosensors, LCPs with
repetitive ionic side chains have been utilized. These systems take
advantage of the polymeric nature of the LCPs, and multivalent non-
covalent interactions between a synthetic polymer, the LCP, and a
natural polymer, i.e., the biomolecule, occur. 7, 13, 50–53 This is something
quite different from what has been accomplished with many fluores-
cent detector dyes over the years. In addition to the covalent attachment
of point-like fluorophores by covalent chemistry to biomolecules,
noncovalent environment-sensitive dyes have been frequently
employed for biomolecular recognition and can provide information
on, e.g., local hydrophobicity and proximity within a complex. In
contrast to stiff small-molecular dye binding, complexation between
a flexible polymer, the LCP, and a biological polymer causes changes