Optical Reporting by Conjugated Polymers via Conformational Changes - Advanced Fluorescence Reporters in Chemistry and Biology - page 414

spectroscopy through a cranial window after an intravenous injection of the penta-
meric dye. Hence, p-FTAA was shown to cross the BBB rather efficiently and
p-FTAA bound to A

deposits showed a characteristic emission spectrum with
well-resolved substructures (Fig. 21c ). This spectral feature is probably a result of
conformational restriction of the thiophene backbone upon binding to the deposits.
Furthermore, in a similar fashion to what was previously reported for the polydisperse
PTAA [ 35 ], p-FTAA emission spectra could be used for assigning two differing
strains of prions (Fig. 21d ). Thus, p-FTAA was also shown to exhibit conformation-
dependent optical properties comparable to the CPs described above. These properties
could also be utilized for spectral separation of the two major pathological hallmarks
of AD, namely neurofibrillary tangles (NFTs) and A

b

b

deposits. As shown in Fig. 21e,

p -FTAA bound to A -deposits emitted green light, whereas the NFTs showed a

red-shifted spectrum for p-FTAA. Thus, the distinctive spectral signatures from
p-FTAA bound to A

b

aggregates or tau deposits may be used to study the interplay
between these entities in more detail. When compared with their larger, polymeric
ancestors, these small chemically defined molecular probes with conjugated systems
serve a much better chance for in vivo applications due to the ability of many to pass
through cellular walls and across the blood-brain barrier.

b

6 Concluding Remarks

In conclusion, CPs and their oligomeric counterparts represent an interesting and
diverse class of molecules that have proven to be useful in a number of applications
in which their inherent fluorescent properties allow for very sensitive and precise
detection using present technology in the field of fluorescence. The phenomenon of
the spectral transition of CPs based upon planarity, backbone conjugation, and
target association continues to prove useful in many new and diverse applications in
fluorescence reporting. Future synthesis of novel, chemically defined oligomeric
CPs will certainly realize combinatorial approaches for optimizing the CPs struc-
ture, which may provide more effective binders for different classes of biomole-
cular targets. To understand and correlate the spectral signature of the CPs to a
distinct biological event, the focus must also be turned to the fundamental under-
lying photo-physical processes of CPs and their related oligomeric counterparts.
As described in this chapter, CPs are being implemented in new areas of science
and we foresee that these materials will continue to evolve and serve as practical
research tools within the fields of biology and pathology.

References

1. Le Bouch N, Auger M, Leclerc M (2008) Structure and segmental motions in a substituted
polythiophene: a solid-state NMR study. Macromol Chem Phys 209:2455-2462
2. Huser T, Yan M, Rothberg L (2000) Single chain spectroscopy of conformational dependence
of conjugated polymer photophysics. Proc Natl Acad Sci 97:11187-11191